OOD BOOT by yaofenji

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									 G OOD B OOT
Getting To Know and Love Your Computer

             Getting To Know Your Computer
Good Boot Computer Walk-About................................................ 1
Good Boot Guide to Your Operating Systems ................................. 31
Good Boot Guide to Your Microprocessor ..................................... 37
Good Boot Guide to Your Hard Disk ........................................... 41
Good Boot Guide to Your Motherboard ........................................ 44
Good Boot Guide to Your IDE Device .......................................... 46
Good Boot Guide to Your AGP .................................................. 48
Good Boot Guide to Your Sound Card ......................................... 50
Good Boot Guide to Your Parallel Ports ....................................... 52
Good Boot Guide to Your Serial Ports Work .................................. 54
Good Boot Guide to Your Computer Memory .................................. 56
Good Boot Guide to Caching .................................................... 60
Good Boot Guide to Your Floppy Disk Drive ................................... 62
Good Boot Guide to Your Monitor .............................................. 64
Good Boot Guide to Your Mouse ............................................... 68
Good Boot Guide to Your Keyboard ............................................ 71
Good Boot Guide to Your CDs & CD Burner ................................... 73
Good Boot Guide to Your DVD ................................................. 79
Good Boot guide to Your Blu-ray Discs ....................................... 85
Good Boot Guide to Your Modem, Cable and DSL............................ 88
Good Boot Guide to Your USB ................................................. 94
Good Boot Guide to Your Flash Memory ...................................... 98
Good Boot Guide to Your MP3 Files .......................................... 100
Good Boot Guide to Your MP3 Player ......................................... 102
Good Boot Guide to File Sharing .............................................. 106
Good Boot Guide to Your Surge Protector ................................... 109
Good Boot Guide to Home Networking ........................................ 113
Good Boot Guide to Your Laptops ............................................. 120
Good Boot Guide to Your PDA ................................................. 129
                                                                Page 1

                                  Getting To Know Your Computer
                                                                                            Computer Types
    Good Boot Computer Walk-About
                                                                       There is a computer for every use under heaven, or so it seems.
                                                                       Let’s look at the kinds of computers that there are, based on
                  What is a computer?                                  general performance levels.
A computer is an electronic device that executes the instructions                           Personal or micro
in a program. A computer has four functions:
a. accepts data = Input                                                Computers for personal use come in all shapes and sizes, from
b. processes data = Processing                                         tiny PDAs (personal digital assistant) to hefty PC (personal
c. produces output = Output                                            computer) towers. More specialized models are announced each
d. stores results = Storage                                            week - trip planners, expense account pads, language transla-
                               The Information Processing Cycle

In the tutorials that follow we will study the parts of the computer
and each of the four parts of the Information Processing Cycle.
                 Some Beginning Terms
Hardware         the physical parts of the computer.
Softwarethe programs (instructions) that tell the
                                                                           Hand-held (HPC)                           PDA
                 computer what to do
Data             individual facts like first name, price, quantity
Information      data which has been massaged into a useful
                 form, like a complete mailing address
Default          the original settings; what will happen if you
                 don’t change anything.
                                                                               Tablet PC                       Laptop/Notebook
       What makes a computer powerful?

                                                                                  Desktop                              Tower
        A computer can do billions of actions per second.

   Failures are usually due to human error, one way or another.

           A computer can keep huge amounts of data.                                            Workstation
                                                                       When talking about PC computers, most people probably think
                                                                       of the desktop type, which are designed to sit on your desk. (Bet
                                                                Page 2
you figured that one out!) The tower and the smaller mini-tower        The supercomputer is the top of the heap in power and expense.
style cases have become popular as people started needing more         These are used for jobs that take massive amounts of calculating,
room for extra drives inside. Repairmen certainly appreciate the       like weather forecasting, engineering design and testing, serious
roominess inside for all the cables and circuit boards ... and their   decryption, economic forecasting, etc.
                                                                                     Distributed or Grid Computing
A workstation is part of a computer network and generally would
                                                                       The power needed for some calculations is more than even a
be expected to have more than a regular desktop PC of most
                                                                       single supercomputer can manage. In distributed computing
everything, like memory, storage space, and speed.
                                                                       using a PC grid many computers of all sizes can work on parts of
The market for the smallest PCs is expanding rapidly. Software is      the problem and their results are pooled. A number of current
becoming available for the small types of PC like the palmtop          projects rely on volunteers with computers connected to the
(PPC) and handheld (HPC). This new software is based on new            Internet. The computers do the work when they are not busy
operating systems like Windows CE (for Consumer Electronics).          otherwise.
You may find simplified versions of the major applications you
                                                                       The projects that need distributed computing are highly techni-
use. One big advantage for the newer programs is the ability to
                                                                       cal. For example, the SETI@Home project looks for signs of
link the small computers to your home or work computer and
                                                                       intelligent communication in radio signals coming from space.
coordinate the data. So you can carry a tiny computer like a
                                                                       (SETI stands for Search for Extra-Terrestrial Intelligence.)
PalmPilot around to enter new phone numbers and appointments
and those great ideas you just had. Then later you can move this       If you volunteer your computer for this project, you might be
information to your main computer.                                     asked to load a small screen-saver program onto your own
                                                                       computer. When the computer is not busy, the screen saver
With a Tablet PC you use an electronic stylus to write on the
                                                                       comes on. The program downloads some signal data, starts to
screen, just like with a pen and paper, only your words are in
                                                                       analyze it, and later reports the results back to SETI@Home.
digital ink. The Tablet PC saves your work just like your wrote it
                                                                       Once the program is installed, you do not have to do anything
(as a picture), or you can let the Hand Recognition (HR) software
                                                                       else but watch the progress in the screen saver.
turn your chicken-scratches into regular text.
                                                                       Another method does not use a screen saver, but uses any idle
                          Main frame                                   time on your computer to work on the project. Results are sent to
                                                                       the project’s home over the Internet.
                                                                                       Other Important Terms

The main frame is the workhorse of the business world. A main
frame is the heart of a network of computers or terminals which
allows hundreds of people to work at the same time on the same
data. It requires a special environment - cold and dry.
                                                                       The term server actually refers to a computer’s function rather
                                                                       than to a specific kind of computer. A server runs a network of
                                                                       computers. It handles the sharing of equipment like printers and
                                                                       the communication between computers on the network. For such
                                                                       tasks a computer would need to be somewhat more capable than
                                                                       a desktop computer. It would need:
                                                                       * more power
                                                                       * larger memory
                                                                       * larger storage capacity
                                                                       * high speed communications
                                                                       The minicomputer has become less important since the PC has
                                                                       gotten so powerful on its own. In fact, the ordinary new PC is
   The first Cray supercomputer was introduced in 1976                 much more powerful than minicomputers used to be. Originally
                       the Cray-1                                      this size was developed to handle specific tasks, like engineering
                                                                       and CAD calculations, that tended to tie up the main frame.
                                                               Page 3
                                                                      Notice the list of commands in the popup menu in the center. You
                What are Applications?                                would use the arrow keys to move up and down the list and then
                      User Interface                                  press the Enter key to execute the command. Various menus are
                                                                      usually available by using the Alt key in combination with a letter
An application is another word for a program running on the           or number key.
computer. Whether or not it is a good application depends on
how well it performs the tasks it is designed to do and how easy                         Graphical Interface
it is for the user to use, which involves the user interface- the     A graphical user interface (GUI - sometimes pronounced GOO-ee)
way the user tells the software what to do and how the computer       uses pictures to make it easier for the user. It is more user
displays information and options to the user.                         friendly.
                      Text Interface                                  The example below is from Windows. The use of drop-down
A text interface was all that was available in the beginning. The     menus, windows, buttons, and icons was first successfully
example to the right is of PKZIP, which squashes files into smaller   marketed by Apple on the Macintosh computer. These ideas are
size to save you space. Notice in the center the command you          now as standard for graphical interfaces as door knobs are for
would have to type to use this program. An actual command line        doors.
would look something like: c:\>pkzip c:\myfiles\newfile.zip
A text-based interface means typing in all the commands. If you
mis-type, you have to backspace to your error, which erases what
you already typed. It’s hard to have fun this way!

                                                                      Common features of a graphical interface: window, menu, button
                                                                      and icon .
Add-on programs were written, of course, so you could edit what       There are many different kinds of applications, all with lots of
was typed - to the joy of all who had to work with long command       spiffy features. Word processing is the application that is used
lines.                                                                most often and most widely. We will start with it to learn about
                                                                      the terms and features that are common to most applications, as
Modern text interfaces have lots of cool shortcuts and features.
                                                                      well as some that are specific to word processing. Then we will
But you still have to spell and type well.
                                                                      look at other major applications and what they do.
Improvements arrived with the addition of menus and the use of
the arrow keys to move around the screen. This is much better         Major word processors include Microsoft Word and
than having to type in all the commands.                              WordPerfect.

The example below is of a bulletin board communications                                     Word processing
program.                                                              Word processing is the most used computer application!
                                                                      It has replaced the typewriter as the main way words are put on
                                                                      paper. Documents can be revised and corrected before they are
                                                                      ever printed. An existing document can be used as a template, or
                                                                      pattern, for a new one. So the user doesn’t have to recreate
                                                                      standard documents from scratch each time. This is a major time-
                                                                      saver and helps keep things consistent.
                                                                      Purpose: To produce documents
                                                                      Main advantage: Can easily change what has been done.
                                                                 Page 4
                Steps to produce a document                           Typeface - set of characters of similar design like:
*   Create                                                                                      Century Gothic
*   Edit
*   Format
*   Print                                                                                         Plump
*   Save (often!!)
                                                                      Point size        one point = 1/72 of an inch like
Let’s look at the terms involved in these steps more closely.
Most of these terms also apply to the other standard applica-
tions, so we will not redefine them for all.
                                                                                        12 pt 18     pt 24 pt          36 pt
                              Create                                  Font              combo of typeface & point size, includes styles
                                                                                        such as BOLD, italics, underline
You create a document when you enter text.                            Margins           space at the page borders
Word wrap      automatically wrapping the text to the next line
                                                                      Justification      left    center right   full
               so it all fits within the screen’s width
Cursor         symbol for where text will appear like:
Enter text     type new text
Scrolling      moving document around within window
Select         Highlight text, usually by dragging. Commands          Spacing           space between letters and lines
               and keystroke combinations will apply to the
               selected material.
Edit           make changes
                                                                      Style sheets      saved sets of formats to reuse
Cut            remove selection from document and store
                                                                      Columns           columns of text side by side
               temporarily on the Clipboard, which is a
                                                                                        as in a newspaper
               section of computer memory. The Windows
               Clipboard can hold only one thing at a time.
               The Office Clipboard from Office XP can hold
                                                                      Tables            items listed in rows and columns
               many items.
Copy           duplicate selection onto Clipboard
Paste          place Clipboard contents at cursor location
                                                                      Graphics          pictures and charts
               Undo - reverses whatever change you just
               made. Some programs will only “undo” the last          Borders/shading              lines around table/page; background
               change. Others keep a list and can undo more,
               depending on how many changes you have
               chosen to track.
Insert         add text at location without overwriting
                                                                      Headers/Footers              lines around table/page; background
               existing text
Delete         remove text (not saved anywhere)
Search         look for specific word(s) or character(s)
Replace        can replace specific word(s) or character(s)
               with stated text
Template       a document that serves as a pattern for a new
Thesaurus      looks for synonyms for selected word                                                  Print
Spelling check looks for spelling errors
Grammar check looks for grammar/style errors (of limited help)        When a document is finished, it may be printed onto paper.
                                                                      Choose number of copies/pages to print
Once a document has been created, or during the process, you
                                                                      Choose Orientation:
arrange how it will look by selecting the kind of letters and their
sizes and colors, how much space is left and where, how things
line up. This is formatting the document.
                                                                                          Portrait Landscape
                                                                      Print Preview shows you how it will look in print
                                                                Page 5
                    Desktop Publishing                                                             Spreadsheet
                           Desktop publishing does on the                               A spreadsheet is the application of choice for
                           computer what used to be done with                           most documents that organize numbers, like
                           scissors and glue and other non-                             budgets, financial statements, grade sheets, and
                           computer methods - put together text                         sales records. A spreadsheet can perform simple
                           and graphics for printing.                                   or complex calculations on the numbers you
                                                                                        enter in rows and columns.
                            High-end word processors can do
                            much of what a desktop publishing
program does, at least for fairly simple documents. The difference     Some popular spreadsheets include MS Excel, Lotus 1-2-3, and
between them has become a bit blurred.                                 Quattro Pro.
Look at a national magazine and try to duplicate the layout and        Purpose: Organizing numbers
graphics quality in a word processor! You will see that there IS a     Major Advantages: Can calculate for you using formulas.
difference.                                                             Auto-update of related numbers when data changes. Can
                                                                        display data in graphs and charts.
For professional publications, a desktop publishing program
gives the precise control needed and also advanced capacities          Features/Terms:
such as preparing four-color separations for commercial printing.      * rows & columns: Creates a grid
                      Levels of Software
“Desktop publishing” covers a wide range of activities and
difficulty levels:
* Professional: Create for commercial printing - magazine,
  company annual report, newspaper, book, fullcolor advertising
* Specialty programs: Make your own greeting cards,                    * cell: Intersection of row and column. Can contain text or
  calendars, or labels. Print T-shirts.                                  numbers.
* Small business/home office: Use a wizard or template to
  create a brochure, business card, or ad and print on your own
Major players in the desktop publishing game include Microsoft
Publisher, QuarkXpress, and several Adobe products -                   * formula: Calculates value to put in cell, like a total, an
PageMaker, FrameMaker and InDesign.                                      average, interest, etc.=SUM(C21:C45)
Purpose: To prepare documents with graphics with precise
 control of the layout
                                                                       * chart: Graphical representation of the data
Major Advantages: Ability to place text and graphics precisely
 on page. Ability to chain sections together like newspaper
 columns. Advanced tools for professional work
Layout:           arranging text and graphics
Clip art:         pre-drawn pictures to add to page                    A database is a collection of data that you want to
WYSIWYG:          What You See Is What You Get pronounced              manage, rearrange, and add to later. It is a good
                  “wiz-e-wig” How page displays on screen is           program to use to manage lists that are not entirely
                  the same as how it prints                            numbers, such as addresses and phone numbers,
Separations:      For full color in high quality printing, the paper   inventories, and membership rosters.
                  goes through the printing press 4 times, once
                                                                        With a database you could sort the data by name or
                  for each of the colors cyan, magenta, yellow,
                                                                       city or postal code or by any individual item of
                  and black (CMYK color system). The print
                                                                       information recorded. You can create forms to enter or update or
                  shop must create separate versions of your
                                                                       just display the data. You can create reports that show just the
                  document, called separations, for each color.
                                                                       data you are interested in, like members who owe dues.
                                                                   Page 6
Both spreadsheets and databases can be used to handle much
the same information, but each is optimized to handle a different
type most efficiently. The larger the number of records, the more
important the differences are.
Some popular databases include MS Access, dBase, FoxPro,
Paradox, Approach, and Oracle.
Purpose: Managing data
Major Advantages: Can change way data is sorted and
A flat database contains files which contain records which
contain fields.

                                                                          A spreadsheet can work as a flat database. Each field is in a
                                                                          separate column and each row is a single record. The example
                                                                          below shows how quickly a record gets wider than the screen.
                                                                          You cannot use two rows for one record.

A relational database contains tables which are linked to-
gether. Each table contains records which contain fields.

                                                                          Relational database: Microsoft Access and Oracle and other
                                                                          relational databases are more advanced and more efficient. This
                                                                          kind of database uses a set of tables which are linked together.
                                                                          Using a well-designed relational database can greatly reduce the
A query can filter your records to show just the ones that meet           amount of data you must enter each time you add a record.
certain criteria or to arrange them in a particular order.                For large numbers of records, a relational database can search
                      Types of databases                                  through the records faster.

Flat database: The earliest and simplest databases are flat               Advantages: Reduces the duplication in data entry. Faster
databases. A flat database may still be all you need for your              searches. Can create forms and reports that display only the
purpose.                                                                    data you want to see. Can create queries to answer questions
                                                                           that are hard or impossible to answer in flat databases.
Advantages: Easy to set up. Easy to understand                            Disadvantages: Can be complex to set up, using many tables.
Disadvantages: May require entering the same information in                It is harder to understand how all the parts relate to each other.
  many records. A text database is hard to read. A single record in       The Figure on Page 7, Column 1 is an illustration of the tables in a
a spreadsheet database may not fit across the screen.                     small database that records information about insurance agents
A text database is a plain text file where the fields are sepa-           and policy holders. This particular insurance office works with
rated by a particular character like a vertical bar | or a comma , or a   several different insurance companies. There are 7 tables in the
semi-colon ; . The example below puts a vertical bar between              database. The lines show which fields in each table are the same.
each field. The first record shows the names of the fields.               These link the tables together.
A text database is hard to read in this raw form. A database              Each agent can be licensed with several different companies and
program can show each record separately in a more readable                in several different states. In a flat database you would have to
display. It is hard to create a report that contains just the parts       have a record for each agent for every company and state he is
you want to see.                                                          licensed with, repeating the agent info for each record. Argh! Too
                                                                          much typing!!
                                                               Page 7

You can design a form so that you can do this all in one spot!
This is much easier than repeating so much information for each         Image 1
record as you would do in a flat database. The image 1 and 2 in
Column 2 show the two screens for the Agent Info Form. This
form can be used for entering new agents as well as for display-
ing the current ones.
You often want to look at just part of the data in a database. You
can reorder or filter your data using Structural Query Language
(SQL). You might want a list of people who have a particular
postal code, for example. Happily there are visual methods you
can use to create your query, like the example below from MS
Access. You can drag the fields from the list at the top and drop
them in the columns at the bottom. You can add sorting orders or
criteria, like picking a particular postal code. The query figure
(Image 1, 2 and Queries brings together the fields from the Agent
Info table that are needed for mailing labels.

The actual SQL code for this query looks a lot different from the
Design view above! No wonder a drag-and-drop method was                 Image 2
Graphics programs deal with pictures, either static or moving, flat
or 3D. There are an amazing number of different formats for
images in the world and no one program can handle them all.
Adobe Photoshop is the most widely used graphics program for
professionals. PaintShopPro is popular because it offers most of
Photoshop’s features at a lower cost and with a friendlier
interface. There are many other programs. Some specialize in
handling photographs or animations or creating logos.
Purpose: To create and edit images

                                                                 Page 8
Paint programs work with                                               Fill colors an enclosed area with one color or pattern.
pictures on a pixel-by-pixel                                           Cel a single image in an animation sequence.
basis, where a pixel is the
smallest dot on the screen.
Such programs handle                                                   A presentation program, also known as presentation graphics,
photographs and most                                                   links together a sequence of slides containing text and graphics.
clipart. MS Paint is this type                                         A slide show might be used for a sales presentation or for
of program.                                                            training or to enhance any kind of speech.
  * Advantages: Control
                                                                       A presentation program includes a number of tools for creating
     over each dot in the
                                                                       graphics that are quite useful. High-end programs can add sound
                                                                       and video to the slides.
  * Disadvantages: Angled
     lines are jagged stair steps,
    especially if enlarged.
Drawing programs, on the
other hand, define images in
terms of vectors, that is,
equations that describe
geometric shapes. Fortu-
nately, the user doesn’t have
to do the math! Drawing
objects in MS Office are
vector images.
  * Advantages: Does not get as fuzzy or jagged when the size
    is changed. The file size is smaller. (For the web, the original
     vector picture at right had to be converted to a bitmap
  * Disadvantages: Can’t change the color of a dot in the                             Three slides from a presentation
    middle of a shape.
Animation and video programs put a set of still pictures into a        Examples of presentation software: Microsoft PowerPoint, Corel
sequence. When the sequence of images is run, the change from          Presentations, Lotus Freelance Graphics.
one picture to the next fools the eye into seeing motion. This is      Purpose: Turning information into visual form
how movies and television work. An individual image in an
animation is called a cel. (Yes, there is just one l in that word!)    Major Advantages: Pictures convey info faster than tables of
                                                                        numbers. Having something to look at helps keep your
The animation of eyes above was made with just 2 cels. The              audience focused on what you are saying.
animation below from Microsoft GIF Animator takes 56 cels!
Bitmap image a picture defined as a series of dots.
Vector image a picture defined as a set of geometric shapes,
  using equations.
Animation a sequence of images that are shown rapidly in
 succession, causing an impression of movement.
Pixel a single picture element, the smallest dot on the screen. A
 period (.) is made of 4 pixels in a square.                                                         Charts
Palette a set of colors

Brush a tool for drawing lines. May give the effect of using a
 pencil, a paint brush, an airbrush spray, chalk, charcoal, felt-tip

Handles shapes on a selected object that allow you to change
  the shape by dragging the handle.
                                                                                              Analytical graphics
                                                               Page 9

Slide show: The whole sequence of slides shown in order
Transition effect: The way a slide changes to the next slide.
 For example the new slide might appear to slide in from the
 side over the old slide.
                                                                              WS_FTP - a program for transferring files
Animation effect: The way part of a slide appears. For ex
 ample, a line might be revealed one letter at a time.                                            Chat
                      Communications                                In a chat program you join a chat room. You write messages that
                                                                    appear in a window that shows all the messages being sent in
                         These programs temporarily connect
                                                                    this chat room. Everyone who is logged in to this room can read
                         computers to each other to exchange
                                                                    your messages.
                         information. They may use telephone
                         lines or dedicated cables for the          The mIRC image is for the program mIRC. Each person listed on
                         connection. This allows you, for           the right is “in” the room and can write messages and all the
                         example, to work at home on the            others can read them. Recent chat programs let users format their
                         weekend and transfer all you’ve done to    text with color and even with different fonts. People in chat
                        your computer at work before you leave      rooms tend to use a lot of abbreviations and smiley faces.
                        home.                                                             Instant Messaging
These are not the same as networking programs where computers       An instant messaging program notifies you when your friends
are actually linked together all the time.                          are online. Then you can send them messages, which they see
Most communications programs now include many different             immediately. Only the one you send the message to can see it
communication functions in one interface.                           and only you can see the messages that are sent to you, unless
                                                                    you choose to change to a multiple-user mode. Recent versions
Purpose: Transmitting data and messages between computers
                                                                    of instant messaging include the ability to use video
Major Advantage: Speed                                              conferencing, to play games together with your friends, and even
                                                                    to make phone calls over the Internet. Examples of instant
A communications program includes one or more of the following
                                                                    messaging programs are ICQ, AOL Instant Messenger, and MSN
                                                                    Messenger Service.
* Sending and receiving files: FTP (File Transfer Protocol)
* Exchanging messages in a group: chat programs                     The image below shows what ICQ messages look like, when there
* Private messages: instant messaging                               are just a few people messaging. You customize the look of the
* Voice messages                                                    messages, of course.
* Video conferencing
* Phone calls over the Internet
               FTP (File Transfer Protocol)
An FTP program manages the moving of files between comput-
ers. When you download a file over the Internet, you are using
an FTP program. Programs like word processors and HTML
editors that can upload files to web sites include this ability
without having to use another program.
The image below is for the program WS_FTP, which is a fairly
typical FTP program. It shows the folder tree for both the source
and destination. You can copy in either direction.

                                                                                 ICQ - an instant messaging program
                                                                Page 10
                             Browser                                                                By linking to the personal scheduling
                                                                                                    programs of the people involved, the
                    An Internet browser is a program that lets
                                                                                                    project management program can see
                    you navigate the World Wide Web. [It’s what
                                                                                                    when meetings can be arranged by
                    you are using to view this page!]
                                                                                                    looking at everyone’s scheduled
                    A browser displays web pages, keeps track of                                    events. It can check for conflicts
                    where you’ve been, and remembers the places                                     between parts of the project and for
                    you want to return to.                                                          deadline errors.
More information is available over the Internet every day, and          Purpose: To plan, schedule, and analyze the events and costs of
more tasks can be done. You can buy books, check on your bank            a project
account, buy and sell stocks, even order pizza over the Internet.
                                                                        Major Advantage: To display a timeline of tasks and to link to
But you have to have a browser to do it.
                                                                         personal scheduling programs.
Internet Explorer is by far the most popular browser, though there
                                                                               Personal Information Manager (PIM)
are many others around. Netscape was once the dominant
browser and is still used, but it is falling further behind in market   PIM’s are a special kind of database. A PIM will normally include
share all the time.                                                     an address book, a calendar to schedule activities and appoint-
                                                                        ments, and a to-do list where you list chores, calls to make,
Purpose: Navigating the Internet
                                                                        various things to do.
Major Advantage: Can display graphics, which older internet
                                                                        Some popular programs which include PIM functions are MS
 applications don’t. Keeps a list of places you want to return to.
                                                                        Outlook, Lotus Organizer, ACT! and Gold Mine. Sidekick was the
                              E-mail                                    first PIM.
E-mail, or electronic mail, is becoming more and more popular as        New versions of these programs add email management, wireless
people learn to communicate again with written words. For many          access, and other features for the new, hot technologies. The
purposes it is superior to a phone call because you don’t have to       new goal for a PIM seems to be to vanish into the background,
catch the person in and you can get straight to the point. No time      while letting you have access to your email, calendar, and
is wasted on casual conversation. It also leaves a written record       scheduling software from anywhere.
to refer back to for a response or if you forget who said what. E-
                                                                        Purpose: Tracking personal information like - appointments,
mail is superior to the traditional office memo because it uses no
                                                                         address book, birthdays, phone messages and notes on future
paper (Save the trees!!) and it can be sent to a whole list of
people instantly.
                                                                        Major Advantage: Quick access to schedule data and address
Commonly used email programs include Microsoft Outlook
                                                                         book. Can often be merged into documents directly.
Express, Microsoft Outlook, Netscape Mail, Eudora, and Pe-
gasus.                                                                                       Contact Manager
Purpose: Transmitting messages between computer users                   An advanced PIM may be called a Contact Manager. Such a
                                                                        program is optimized to make it easy to track who you have
Major Advantage: Speed
                                                                        talked to or met with and what you did or said.
Major Disadvantage: You don’t know if the receiver actually
 reads it, though you can find out if they received it. Of course       A contact manager automatically links a name in the address
 in a phone conversation you don’t really know if the person is         book to names in the calendar. Clicking on the name in the
 actually listening either!                                             calendar brings up the full contact information, including fields
 With no body language or vocal intonations it is difficult to          for notes about what you did and reminders for what you need to
 convey the emotional tone you want. Irony and sarcasm are              do after the meeting or conversation. From the address book you
 particularly dangerous since your reader may take you                  can bring up a list of when you had contacts with this person.
 seriously.                                                             Powerful stuff!

                    Project Management                                               Integrated Software Suites

When you have a group of people working together on a                   Integrated software combines the functions of several programs
complex project, you need a way to manage all the details. A            into one interface. Such a program is usually designed for the
project management program, like Microsoft Project 2000, tracks         beginning or casual user.
all of the people, tasks, and deadlines in a major project.             Many advanced features are omitted that might be found in
                                                                        stand-alone products. For example, the word processor in an
                                                               Page 11
integrated software package would not likely have a way to             Commands are special codes or key words that the user inputs to
automatically generate a table of contents and would have fewer        perform a task, like RUN “ACCOUNTS”. These can be selected
options on how to handle footnotes, headers, and footers.              from a menu of commands like “Open” on the File menu. They
                                                                       may also be chosen by clicking on a command button.
Microsoft Works is an example of integrated software.
                                                                       User response is the user’s answer to the computer’s question,
                                                                       such as choosing OK, YES, or NO or by typing in text, for
                                                                       example the name of a file.
                                                                       The first input device we will look at is the Keyboard. The image
                                                                       used on the next page to illustrate the various keys may not look
                                                                       like the keyboard you are using. Several variations are popular
                                                                       and special designs are used in some companies. The keyboards
                                                                       shown below put the function keys in different places. The Enter
A software suite is a set of applications which can each stand         and Backspace keys are different shapes and sizes. One has
alone. They are packaged together for a lower price than if all        arrow keys while the other doesn’t. It’s enough to confuse a
were bought separately. There are usually enhancements that            person’s fingers!!
help the applications communicate with each other, also.
Some popular suites of office software include MS Office, Lotus
Smart Suite, and WordPerfect Office. These include a number of
other programs, such as: word processing, spreadsheet, presen-
tations, e-mail client, address book and database.
An example of a graphics suite is Corel Draw Suite, which
includes programs for: vector illustration, layout, bitmap creation,
image-editing, painting and animation software.
An example of a publishing suite is Adobe Publishing Collec-
tions, which includes: Adobe PageMaker - desktop publishing,
Adobe Photoshop - bitmap graphics, Adobe Illustrator - vector
graphics, Adobe Acrobat - converts documents to Portable               The backslash key has at least 3 popular placements: at the end
Document Format for sharing.                                           of the numbers row, above the Enter key, and beside the Enter
Purpose: Linking different applications together for better work
                                                                       key. We also have the new Windows keyboards which have two
(integrated software) simplifying things for new users                 new keys. One pops up the Start Menu and the other displays
                                                                       the right-click context sensitive menu.
Major Advantage: Costs less than a set of similar stand alone
  applications bought separately                                       Ergonomic keyboards even have a different shape, curved to fit
Major Disadvantage: (integrated software) Lacks many
                                                                       the natural fall of the wrists.
 features of the stand-alone versions of the same software.
 (suites) You may not need all the parts or the advanced features
 in the collection.

                      What is Input?                                                         Pointing Devices
         Everthing we tell the computer is Input
                                                                       A variety of pointing devices are used to move the cursor on the
                                                                       The most commonly used ones have two or three buttons to click
                                                                       for special functions.

                       Types of Input
                                                                       Mouse: A ball underneath rolls as the mouse moves across the
Data is the raw facts given to the computer.                           mouse pad. The cursor on the screen follows the motion of the
Programs are the sets of instructions that direct the computer.
                                                             Page 12
mouse. Buttons on the mouse can be clicked or double-clicked to      Game Devices: Cursor motion controlled by vertical stick
perform tasks, like to select an icon on the screen or to open the   (joystick) or arrow buttons (gamepad)
selected document.
There are new mice that don’t have a ball. They use a laser to
sense the motion of the mouse instead. High tech!
Advantage: Moves cursor around the screen faster than using
Disadvantage: Requires moving hand from keyboard to mouse
 and back.
Danger: Repeated motion can lead to carpal tunnel syndrome           Advantage: A joystick gives a more natural-feeling control for
                                                                       motion in games, especially those where you are flying a plane
                                                                       or spaceship. Both have more buttons for special functions
                                                                       a mouse and can combine buttons for even more actions.
                                                                     Disadvantage: More expensive. Bulky. Better ones require an
                                                                       additional peripheral card for best performance.
Trackball: Instead of moving the whole mouse around, the
user rolls the trackball only, which is on the top or side.
Advantage: Does not need as much desk space as a mouse.
 Is not as tiring since less motion is needed.
Disadvantage: Requires fine control of the ball with just one
 finger or thumb.
Caution: Repeated motions of the same muscles is tiring and can
 cause carpal tunnel syndrome.

                                                                     Pen Input: Used esp. in Personal Digital Assistants (PDA).
                                                                     Pen Input is used for:
                                                                     Data Input - by writing. PDA recognizes your handwriting. (If
                                                                     only your friends could, too!)
Glidepad: Uses a touch sensitive pad for controlling cursor.         Pointing Device - Functions like a mouse in moving a cursor
The user slides finger across the pad and the cursor follows the     around the screen and clicking by tapping the screen.
finger movement. For clicking there are buttons, or you can tap      Command Gestures - You can issue commands by moving pen
on the pad with a finger. The glidepad is a popular alternate        in patterns. So a certain kind of swirl would mean to save the file
pointing device for laptops.                                         and a different kind of swirl could mean to open a new file.
Advantage: Does not need as much desk space as a mouse.
                                                                     Advantage: Can use handwriting instead of typing. Can use
 Can readily be built into the keyboard. Has finer resolution.        gestures instead of typing commands. Small size.
 That is, to achieve the same cursor movement onscreen takes         Disadvantage: Must train device to recognize handwriting.
 less movement of the finger on the glidepad than it does mouse       Must learn gestures or train device to recognize the ones you
 movement. Can use either buttons or taps of the pad for              create. Can lose the pen which is not usually attached to the
 clicking.                                                            device
Disadvantage: The hand tires faster than with a mouse since
 there is no support. Some people don’t find the motion as
 natural as a mouse.

                                                                     Touchscreen: Make selection by just touching the screen.
                                                                     Advantage: It’s natural to do - reach out and touch something.
                                                                     Disadvantage: It’s tiring if many choices must be made.
                                                                      It takes a lot of screen space for each choice since fingers are
                                                                      bigger than cursors.
                                                               Page 13
                                                                     A point-of-sale terminal (POS) is an example of a special
                                                                     purpose terminal. These have replaced the old cash registers in
                                                                     nearly all retail stores. They can update inventory while calculat-
                                                                     ing the sale. They often have special purpose keys.
                                                                     For example, McDonalds has separate touchpads for each food
                                                                     item available.
Digitizers and Graphics Tablets: Converts drawings,
photos, etc. to digital signal. The tablets have special commands    Multimedia is a combination of sound and images with text and
                                                                     graphics. This would include movies, animations, music, people
Advantage: Don’t have to redraw graphics already created             talking, sound effects like the roar of a crowd and smashing
Disadvantage: Expensive                                              glass.

                                                                     Sound Input: Recording sounds for your computer requires
                                                                     special equipment. Microphones can capture sounds from the air
                                                                     which is good for sound effects or voices. For music the best
                             Terminals                               results come from using a musical instrument that is connected
A terminal consists of a keyboard and a screen so it can be          directly to the computer. Software can combine music recorded at
considered an input device, especially some of the specialized       different times. You could be a music group all by yourself -
types.                                                               singing and playing all the parts!

Some come as single units.
Terminals are also called:
* Display Terminals
* Video Display Terminals or VDT

                                                                     Voice Input: Voice input systems are now becoming available
                                                                     at the local retail level. You must be careful to get the right
                                                                     system or you’ll be very disappointed.
                                                                     Decide first what you want to do since a voice input program
A dumb terminal has no ability to process or store data. It is       may not do all of these:
linked to minicomputer, mainframe, or super computer. The
                                                                     Data entry - Talking data into the computer when your hands
keyboard and viewing screen may be a single piece of equipment.
                                                                      and eyes are busy should certainly be more efficient. You’d
An intelligent, smart, or programmable terminal can process           have to be very careful about your pronunciation!
or store on its own, at least to a limited extent. PCs can be used   Command and control - Telling the computer what to do
as smart terminals.                                                   instead of typing commands, like saying “Save file”. Be careful
                                                                       here, too. The dictionary of understood words does not include
                                                                      some of the more “forceful” ones.
                                                                     Speaker recognition - Security measures can require you to
                                                                      speak a special phrase. The computer must recognize your
                                                                      voice to let you in.
                                                                     Speech to text - Translating spoken words direct to type
                                                                      would suit some authors just fine. You’d have to watch out for
                                                                      those “difficult to translate” phrases like “hmmm” and “ah,
                                                                      well, ... ummm.”
                                                                     Speech recognition and speech-to-text software is getting better
                                                                     rapidly. At least one retail version has the training period down to
                                                               Page 14
5 minutes and ignores those filler phrases like “ummm”. This is
getting exciting and actually useful!
A number of companies are now using speech recognition in
their telephone systems. For example to find out what your bank
account balance is, instead of punching in your account number
on the phone keypad and choosing option 3 for current balance,
                                                                    A video camera or recorder (VCR) can record data that
you could speak your account number and say “Current bal-
                                                                    can be uploaded to the computer with the right hardware.
ance”. The computer will even talk back and tell you what it
                                                                    Though it is not digital data, you can still get good results with
thinks you said so you can make corrections. Wow!
                                                                    the right software.
                                                                    Both of these take huge amounts of storage. Photos make for
                                                                    very large files.

                                                                    QuickCam by Connectix is a newcomer to the video world. It
How do they change voice to data?
                                                                    is a tiny video camera designed especially to sit on your com-
1. Convert voice sound waves to digital form (digital signal        puter. It feeds pictures directly to the computer - no tape or film
   processing -DSP)                                                 to develop. Of course you are limited by the length of the cable
2. Compare digitized voice input to stored templates                that connects the camera to the computer. But like any camera, it
3. Check grammar rules to figure out words                          will take a picture of what you point it at!
4. Present unrecognized words for user to identify
                                                                    So what do people do with QuickCam? They use it for video
Types of Voice Recognition systems :                                conferencing over the Internet. They show the world what’s
Speaker dependent system: The software must be trained to           going on outside their window (weather, traffic). They take digital
 recognize each word by each individual user. This might take       pictures and make movies- family, pets, snow storms, birthday
 hours of talking the dictionary into the computer, to be           parties, whatever.
 optimistic.                                                                              Data Automation
Speaker independent system: The software recognizes words
 from most speakers with no training. It uses templates. A strong   The first goal of data automation is to avoid mistakes in data
  accent would defeat the system, however.                          entry by making the initial entering of the data as automatic as
Discrete speech recognition: The speaker must pause                 possible. Different situations require different methods and
between                                                             equipment. A second goal of data automation is to avoid having
 words for the computer to tell when a word stops.                  to re-enter data to perform a different task with it.
Continuous speech recognition: The speaker may use normal           For example, the old style cash register would add up your
 conversational flow.                                               purchase and calculate the tax. The clerk entered the amounts by
Natural language: The speaker could say to the computer             hand (the data entry part). Later the numbers off the store copy
 “How soon can we ship a dozen of product #25 in blue to            of the cash register tapes would have to be added up manually,
 Nashville?” - and get an answer!!                                  or entered into a computer program (another data entry task). For
                             Video                                  an up-to-date inventory someone would have to go count all the
                                                                    things on the shelves (a third data entry task).
                                                                    With modern data automation, using bar codes on every item in
                                                                    the store, a computer check-out register along with a bar code
                                                                    scanner will calculate the sale plus transfer the information
                                                                    directly to the computer that does the store bookkeeping plus
A digital camera takes still photos but records the pictures on     adjust the inventory records by subtracting the items just sold.
computer disks or memory chips. The information contained can       The human errors possible at each step of data entry are now
be uploaded to a computer for viewing.                              avoided. Of course, there are still ways for errors to occur, just
                                                                    not as many. In addition, a new feature is available with comput-
                                                                    erized cash registers - a receipt that states the name of the item
                                                                    bought as well as the price.
                                                               Page 15
                       General Devices

Page scanner - The scanner works like a copy machine. It
captures a whole page and converts it to digital image. It cannot     Magnetic Ink - Bank account # is printed in special ink with
be edited at this point.                                              magnetic qualities which can be read by the right machine.

Hand scanner - You move the device across the document or
picture. It will capture only a section of a page or a large image.
So the pieces of anything wider than the scanner would have to
be recombined with some nifty software.
                                                                      Optical Characters - There are coding systems that use
              Special types of characters                             letters or special characters that are especially shaped to be easy
               read with special devices                              for machines to read.
                                                                                              OCR software
                                                                      Optical Character Recognition: This software takes a scanned
                                                                      image and converts the characters in the image into computer
                                                                      characters. The document can now be edited with a word
                                                                      processor. This is a very tricky process. Documents must be
                                                                      carefully checked for wrong conversions. If the original print was
Bar Codes - Retail shops now use printed bar codes on                 not very crisp and clean, errors are very likely. Manually check-
products to track inventory and calculate the sale at the checkout    ing for proper translation is necessary. These programs are
counter. The US Post Office uses bar codes to sort mail, but the      getting really good if they have a clear scan to work with.
bars are different from those used for pricing products.                                    Data      Accuracy
                                                                      A famous slogan in computing sums up the importance of
                                                                      accurate data:
                                                                                  GIGO = Garbage In, Garbage Out
                                                                      Conclusions are no better than the data they are based on.
                                                                      A major task for any program that accepts data is to try to
                                                                      guarantee the accuracy of the input. Some kinds of errors cannot
                                                                      be caught but many of the most common kinds of mistakes can
                                                                      be spotted by a well-designed program.
                                                                      A program should attempt to do the following:
Optical Marks - example - test scoring. A special machine
“reads” the marks. Woe to the student who takes a test with this      1. Test data type and format
kind of score sheet and doesn’t get those bubbles colored in             Example: 2/a/96 is not a date.
correctly!                                                              Example: If a phone number should have exactly 10 digits
                                                                         with the area code, then 555-123 is not acceptable.
                                                                      2. Test data reasonableness
                                                                        Example: 231 should not be a person’s age
                                                                       Example: A sale of $50,000 worth of chewing gum at the
                                                                       corner market is probably missing a decimal point somewhere!
                                                             Page 16
3. Test data consistency                                             strangers. You don’t recognize Mom’s face because you remem-
  Example: A man’s death date should be later than his birth         ber than Mom’s nose is 4 cm long, 2.5 cm wide, and has a freckle
  date!                                                              on the left side! You recognize the whole pattern of Mom’s face.
  Example: The sum of the monthly paychecks should be the            There are probably a lot of folks with noses the size and shape of
  same as the total pay for the year.                                Mom’s. But no one has her whole face.
4. Test for transcription and transposition errors
                                                                     But a computer must have a lot of specific facts about a face to
 Example: Typing 7754 instead of 7154 is a transcription error,
                                                                     recognize it. Teaching computers to pick Mom’s face out of a
  typing the wrong character.
                                                                     crowd is one of the hardest things scientists have tried to do yet
 Example: Typing 7754 instead of 7745 is a transposition error,
                                                                     with computers. But babies do it naturally!
  interchanging two correct characters.
                                                                     So computers can’t think in the same way that people do. But
Both are very hard to check for.
                                                                     what they do, they do excellently well and very, very fast.
                  What is Processing?                                                          Digital Data
                                                                     Modern computers are digital, that is, all info is stored as a string
                                                                     of zeros or ones - off or on. All the thinking in the computer is
                                                                     done by manipulating these digits. The concept is simple, but
                                                                     working it all out gets complicated.

Processing is the thinking that the computer does - the calcula-
tions, comparisons, and decisions. People also process data.
What you see and hear and touch and feel is input. Then you
connect this new input with what you already know, look for how
it all fits together, and come up with a reaction, your output.
“That stove is hot. I’ll move my hand now!”                          1 bit = one on or off position
The kind of “thinking” that computers do is very different from      1 byte = 8 bits
what people do.
                                                                     So 1 byte can be one of 256 possible combinations of 0 and 1.
Machines have to think the hard way. They do one thing at a          Numbers written with just 0 and 1, are called binary numbers.
time, one step at a time. Complex procedures must be broken
down into very simple steps. Then these steps can be repeated        Each 1 is a power of 2 so that the digits in the figure represent the
hundreds or thousands or millions of times. All possible choices     number:
can be tried and a list kept of what worked and what didn’t.         = 2 to the 7th power + 0 + 2 to the 5th power + 0 + 2 to the 3rd
                                                                       Power + 2 to the second power+ 0 +0
People, on the other hand, are better at recognizing patterns than   = 128 +0 +32 + 0 + 8 + 4 + 0 + 0
they are at single facts and step-by-step procedures. For            = 172
                                                                     Every command and every input is converted into digital data, a
                                                                     string of 0’s and 1’s.
                                                                                              Digital Codes
                                                                     All letters, numbers, and symbols are assigned code values of 1’s
                                                                     and 0’s. A number of different digital coding schemes are used by
                                                                     digital devices.
                                                                     Three common code sets are:
                                                                     ASCII (used in UNIX and DOS/Windows-based computers)
                                                                     EBCDIC (for IBM System 390 main frames)
                                                                     Unicode (for Windows NT and recent browsers)
example, faces are very complex structures. But you can identify     The ASCII code set uses 7 bits per character, allowing 128
hundreds and even thousands of different faces. A human can          different characters. This is enough for the alphabet in upper
easily tell one face from another, even when the faces belong to     case and lower case, the symbols on a regular English typewriter,
                                                                  Page 17
and some combinations reserved for internal use. An extended            In an odd parity system the number of on bits would have to be
ASCII code set uses 8 bits per character, which adds another 128        odd. For our example number 10101100, there are 4 on bits (the
possible characters. This larger code set allows for foreign            1’s), so the parity bit is set to on, that is 1, to make a total of 5 on
languages symbols and several graphical symbols.                        bits, an odd number.
ASCII has been superceded by other coding schemes in modern             If the number of on bits is wrong, an error has occurred. You
computing. It is still used for transferring plain text data between    won’t know which digit or digits are wrong, but the computer will
different programs or computers that use different coding               at least know that a mistake occurred.
                                                                        Memory chips that store your data can be parity chips or non-
                                                                        parity chips. Mixing them together can cause odd failures that are
                                                                        hard to track down.

                                                                        The CPU, or Central Processing Unit, is the part of the computer
Unicode uses 16 bits per character, so it takes twice the storage       where work gets done. In most computers, there is one process-
space that ASCII coding, for example, would take for the same           ing chip.
characters. But Unicode can handle many more characters. The
goal of Unicode is to represent every element used in every             Main Memory stores the commands that the CPU executes and
script for writing every language on the planet. Whew! Quite a          the results.
task!                                                                                               Control Unit
Version 3 of Unicode has 49,194 characters instead of the wimpy         This is the part of the computer that controls the Machine Cycle.
few hundred for ASCII and EBCDIC. All of the current major              It takes numerous cycles to do even a simple addition of two
languages in the world can be written with Unicode, including           numbers.
their special punctuation and symbols for math and geometry.
At the Unicode site you can view sections of the Unicode code
table. The complete table is too long to put on one page!               Stands for Arithmetic/Logic Unit. This is the part that executes
                                                                        the computer’s commands. A command must be either a basic
                               Parity                                   arithmetic operation: + - * / or one of the logical comparisons:
                                                                        > < = not =.
With all these 0’s and 1’s, it would be easy for the computer to
make a mistake! Parity is a clever way to check for errors that         Everything else has to be broken down into these few opera-
might occur during processing.                                          tions. Only one operation is done in each Machine Cycle.
In an even parity system an extra bit (making a total of 9 bits) is     The ALU can only do one thing at a time but can work very, very
assigned to be on or off so as to make the number of on bits            fast.
even. So in our example above 10101100 there are 4 on bits (the
                                                                                                Operating System
four 1’s). So the 9th bit, the parity bit, will be 0 since we already
have an even number of on bits.                                         This is the instructions that the computer uses to tell itself how it
                                                                        “operates”. It’s the answer to “Who am I and what can I do?”
                                                               Page 18
Some common operating systems are DOS, various versions of                                 The Machine Cycle
Windows, OS/2, UNIX, LINUX, System 7. These all behave in
very different ways and have different hardware requirements. So
they won’t all run on all machines.
These are the various programs that are currently running on the
By taking turns with the Machine Cycle, modern computers can
have several different programs running at once. This is called
Each open application has to have some data stored in Main
Memory, even if the application is on rest break and is just sitting
there. Some programs (graphics programs are notorious for this)
require a lot of the Main Memory space, and may not give it up
even if they are shut down! Rather rude, actually!!                    Fetch - get an instruction from Main Memory
                                                                       Decode - translate it into computer commands
                    Input/Output Storage
                                                                       Execute - actually process the command
When you enter new data, the keystrokes must be stored until           Store - write the result to Main Memory
the computer can do something with the new data.
                                                                       For example, to add the numbers 5 and 6 and show the answer on
When you want data printed out or displayed, it must be stored         the screen requires the following steps:
somewhere handy first.                                                 1. Fetch instruction: “Get number at address 123456”
                       Working Storage                                 2. Decode instruction.
                                                                       3. Execute: ALU finds the number. (which happens to be 5)
The numbers and characters that are the intermediate results of        4. Store: The number 5 is stored in a temporary spot in Main
computer operations must be stored until the final values are            Memory.
calculated. These values “in progress” are kept in temporary           5 - 8 Repeat steps for another number (= 6)
locations.                                                             9. Fetch instruction: “Add those two numbers”
For example, if the computer is adding up the numbers 3, 5, and 6,     10. Decode instruction.
it would first add 3 to 5 which yields a value of 8. The 8 is stored   11. Execute: ALU adds the numbers.
in working storage. Then the 8 and 6 are added and the new             12. Store: The answer is stored in a temporary spot.
value 14 is stored. The value of 14 is now available to be dis-        13. Fetch instruction: “Display answer on screen.”
played on the screen or to be printed or to be used in another         14. Decode instruction.
calculation.                                                           15. Execute: Display answer on screen.

                        Unused Storage                                 The immense speed of the computer enables it to do millions of
                                                                       such steps in a second.
One hopes that there is always some storage space that is not in
use.                                                                   In fact, MIPS, standing for millions of instructions per second, is
                                                                       one way to measure computer speeds.
If space runs out in Main Memory, the computer will crash, that
is, stop working.                                                                           Memory Address
There are programs that sense when space is getting short and          We need a method of naming the places where Main Memory
warn the user. The user could then close some of the open              stores data.
applications to free up more space in Main Memory. Sometimes
                                                                       Each location needs a unique name, just like houses in a town
the warning is too late to prevent the crash. Remember that all the
                                                                       need a unique street address.
data in Main Memory vanishes when the power goes off. Thus a
crash can mean a lot of lost work.                                                      See Figure 1 and 2, Page 19.

                       Machine Cycle                                   Rather than a street name and house number, memory addresses
                                                                       are just numbers.
The computer can only do one thing at a time. Each action must
be broken down into the most basic steps. One round of steps           A memory address holds 1 byte of data where
from getting an instruction back to getting the next instruction is    1 bit = 0 or 1, on or off
called the Machine Cycle.                                              1 byte = 8 bits
                                                                       1 kilobyte (K or KB) = 1024 bytes
                                                                       1 megabyte (MB) = 1024 kilobytes
                                                               Page 19
                                                                                   Processor Speed affected by:

                                                                       System clock rate = rate of an electronic pulse used to
                                                                       synchronize processing (Only one action can take place between
                                                                       pulses.) Measured in megahertz (MHz) where 1 MHz = 1 million
                             Figure 1                                  cycles per second. This is what they are talking about if they say
                                                                       a computer is a 700 MHz machine. It’s clock rate is 700 million
                                                                       cycles per second.
                                                                       Bigger number = faster processing

                                                                       Bus width = the amount of data the CPU can transmit at a time to
                             Figure 2                                  main memory and to input and output devices. (Any path bits
                                                                       travel is a bus.) An 8-bit bus moves 8 bits of data at a time. Bus
You might wonder why 1024 instead of 1000 bytes per kilobyte.          width can be 8, 16, 32, 64, or 128 so far. Think of it as “How many
That is because computers don’t count by tens like people.             passengers (bits) can fit on the bus at once to go from one part
Computers count by twos and powers of 2. 1024 is 2 x 2 x 2 x 2 x 2     of the computer to another.”
x 2 x 2 x 2 x 2 x 2, that is 2 times itself ten times. It’s a rather
                                                                       Bigger number = faster transfer of data
convenient size number (for computers!).
Update: Things are changing faster than I can type! The
explanation above is no longer entirely true (July 2000). Different
scientific and technical areas are using the words differently. For
data storage devices and telecommunications a megabyte is
1, 000, 000 bytes. For data transmission in LANs a megabyte is
1, 048, 576 bytes as described above. But for data storage on a
floppy disk a megabyte is 1, 024, 000 bytes!
                                                                       Word size = a word is the amount of data the CPU can process
A new set of words has been created to make it clear what size is
                                                                       at one time. An 8-bit processor can manipulate 8 bits at a time.
really being used. See http://physics.nist.gov/cuu/Units/
                                                                       Processors can be 8-, 16-, 32-, or 64-bit so far.
binary.html for a further explanation.
                                                                       Bigger the number = faster processing
                     Processing Speed
                                                                       You want a nice match between the word size and the bus size
We all are impatient and want our computer to work as fast as          and the clock. It wouldn’t do any good to have a bus that can
possible, and certainly faster than our next door neighbor the         deliver data 128 bits at a time, if the CPU can only use 8 bits at a
guy’s at the next desk!                                                time and has a slow clock speed. A huge line of data would form,
Many different factors determine how fast your computer gets           waiting to get off the bus! When computers gets clogged like
things done. Processor speed is one factor. But what determines        that, bad things can happen to your data. It’s like people waiting
the processor’s speed?                                                 to get in the theater. After a while, some of them may leave!!
                                                                                          Physical Components
                                                                       There are several physical components of a computer that are
                                                                       directly involved in processing. The processor chip itself, the
                                                                       memory devices, and the motherboard are the main ones.
                                                                Page 20
                                                                      Some motherboards require that all slots be filled and that all
                                                                      slots contain the same size memory board. It can get frustrating
                                                                      as there are no warning labels about this!

Microprocessor - a single silicon chip containing CPU, ALU,                                   Motherboard
and some memory.                                                      Here we see a diagram and a photo of a motherboard (or main
The ROM (Read Only Memory) cannot be changed by the user              circuit board).
and contains the minimum instructions the computer needs to get       This one is suitable for a Pentium CPU. Nothing has been
started, called booting.                                              plugged in or attached yet.
There may also be another chip dedicated to calculations.
The microprocessor chip is located on a large circuit board called
the main board or motherboard.
                               The physical size of a computer
                               chip is very small, as the ant below

                       Memory Devices
                          Vacuum tube
The oldest type. Didn’t hold up long and generated a lot of heat.
Small metal rings. Magnets tip a ring to left or right, which
represents on and off. Relatively slow.
The integrated circuit on a chip. This is what modern computers
use for memory. Pictured below is a 72-pin SIMM.                      Storage refers to the media and methods used to keep informa-
                                                                      tion available for later use. Some things will be needed right away
                                                                      while other won’t be needed for extended periods of time. So
                                                                      different methods are appropriate for different uses.
                                                                      Remember from my previous tutorials all the kinds of things that
                                                                      are stored in Main Memory.

Memory speed measures the time it takes to move data in or out
of memory. It is measured differently for different kinds of
memory chips:
* in nanoseconds (ns ) for EDO and FPM (smaller is faster)
  1 ns = 1 billionth of a second.
* in MHz (higher is faster) for SDR SDRAM, DDR, SDRAM,
  and RDRAM.
The capacity of a memory chip is measured in megabytes. Sizes
are measured in megabytes and come in powers of 2: 1, 4, 8, 16,
32, 64, or 128 MB on one memory board. Several such boards can
be installed in the computer to increase the amount of RAM                                      Main Memory
(Random Access Memory) available as Main Memory.
Motherboards have only so many slots for memory so there are                           Thus, Primary Storage is Main Memory. This
limits.                                                                                keeps track of what is currently being pro-
                                                                                       cessed. It’s volatile. (power off erases all data).
                                                                                       For Main Memory, computers use RAM, or
                                                               Page 21
Random Access Memory. This uses memory chips and is the                                          Hard Disks
fastest but most expensive type of storage.
                                                                                                     These consist of 1 or more metal
     Secondary Storage is called Auxiliary Storage                                                   platters which are sealed inside a
                                                                                                     case. The metal is one which is
                                                                                                     magnetic. The hard disk is usually
                                                                                                     installed inside the computer’s case,
                                                                                                     though there are removable and
                                                                                                     cartridge types, also.

                                                                      Technically the hard drive is what controls the motion of the hard
This is what is not currently being processed. This is the stuff      disks which contain the data. But most people use “hard disk”
“filed away”, but ready to be pulled out when needed. It is           and “hard drive” interchangeably. They don’t make that mistake
nonvolatile. (power off does not erase)                               for floppy disks and floppy drives. It is clearer with floppies that
Auxiliary Storage is used for:                                        the drive and the disk are separate things.
* Input - data & programs                                                                       Disk Format
* Output - saving results of processing
                                                                      All magnetic disks are similarly formatted, or divided into areas,
So, Auxiliary Storage is where you put last year’s tax info,          called tracks, sectors and cylinders.
addresses for old customers, programs you may or may not ever
use, data you entered yesterday - everything that is not being        The formatting process sets up a method of assigning addresses
used right now.                                                       to the different areas. It also sets up an area for keeping the list of
                                                                      addresses. Without formatting there would be no way to know
                       Magnetic Discs                                 what data went with what. It would be like a library where the
Of the various types of Auxiliary Storage, the types used most        pages were not in books, but were scattered around on the
often involve some type of magnetic disk. These come in various       shelves and tables and floors. You’d have a hard time getting a
sizes and materials, as we shall see. This method uses magnetism      book together. A formatting method allows you to efficiently use
to store the data on a magnetic surface.                              the space while still being able to find things.

Advantages: high storage capacity, reliable and gives direct                                         Tracks
access to data
A drive spins the disk very quickly underneath a read/write head,
which does what its name says. It reads data from a disk and
writes data to a disk. (A name that actually makes sense!)
                 Types of Magnetic Disks
                    Diskette / Floppy Disk
                                                                      A track is a circular ring on one side of the disk. Each track has a
                                                                      number. The diagram shows 3 tracks.
                                                                                             A disk sector is a wedge-shape piece of the
Sizes:       5¼”                                 3½”                                         disk, shown in light gray. Each sector is
Both sizes are made of mylar with an oxide coating. The oxide
provides the magnetic quality for the disk. The “floppy” part is                             On a 5¼” disk there are 40 tracks with 9
what is inside the diskette covers - a very floppy piece of plastic                          sectors each.
(i.e. the mylar)                                                                             On a 3½” disk there are 80 tracks with 9
                 Other Removable Media                                                       sectors each.
                                                                      So a 3½” disk has twice as many named places on it as a 5¼” disk.
Several other kinds of removable magnetic media are in use, such
as the popular Zip disk. All of these have a much higher capacity     A track sector is the area of intersection of a track and a sector,
than floppy disks. Some kinds of new computers come without a         shown in gray. See Figure Track Sector, Page 22.
floppy disk drive at all.
Each type of media requires its own drive. The drives and disks
are much more expensive than floppy drives and disks, but then,
you are getting much larger capacities.
                                                               Page 22
                                                                     The computer keeps track of what it has put where on a disk by
                                                                     remembering the addresses of all the sectors used, which would
                                                                     mean remembering some combination of the cylinder, track, and
                                                                     sector. Thank goodness we don’t have to remember all these
                                                                     Where the difference between addressing methods shows up is
                                                                     in the time it takes for the read/write head to get into the right
                                                                     position. The cylinder method writes data down the disks on the
                          Track Sector.                              same cylinder. This works faster because each metal platter has a
                                                                     read/write head for each side and they all move together. So for
                          Hard Disks                                 one position of the read/write heads, the computer can put some
                         A cluster is a set of track sectors,        data on all the platters before having to move the heads to a new
                         ranging from 2 to 32 or more, depending     position.
                         on the formatting scheme in use.                    What happens when a disk is formatted?
                         The most common formatting scheme for       1. All data is erased. Don’t forget this!!
                         PCs sets the number of track sectors in a   2. Surfaces are checked for physical and magnetic defects.
                         cluster based on the capacity of the        3. A root directory is created to list where things are on the disk.
                         disk. A 1.2 gig hard drive will have
                          clusters twice as large as a 500 MB hard
1 cluster is the minimum space used by any read or write. So
there is often a lot of slack space, unused space, in the cluster
beyond the data stored there.
There are some new schemes out that reduce this problem, but it                              Disk Capacity
will never go away entirely.
                                                                     The capacity of a magnetic disk depends on several factors.
The only way to reduce the amount of slack space is to reduce
                                                                     We always want the highest amount of data stored in the least
the size of a cluster by changing the method of formatting. You
                                                                     possible space. (People are so greedy this way!) So the capaci-
could have more tracks on the disk, or else more sectors on a
                                                                     ties of storage media keep increasing while cost keeps decreas-
track, or you could reduce the number of track sectors in a
                                                                     ing. It’s a lovely situation for the user!
                                                                     Capacity of a Disk depends on:
                                                                     1. # of sides used:
A cylinder is a set of matched tracks.
On a double-sided floppy, a track from the top surface and the
same # track from the bottom surface of the disk make up a
cylinder. The concept is not particularly useful for floppies.


On a hard disk, a cylinder is made of all the tracks of the same #
from all the metal disks that make up the “hard disk”.
If you put these all together on top of each other, you’d have
something that looks like a tin can with no top or bottom - a

                                                                Page 23
2. Recording density - how close together the bits can be            Clearly, getting data from a hard disk is immensely faster than
on a track sector of the innermost track                             from a floppy.
                                                                                          Caring For Disks
                                                                     To keep your storage media happy and healthy you must
                                                                     observe certain precautions.

3. # of tracks on the disk                                           Each medium has its own particular weaknesses and hazards to
                                                                     avoid. Be careful or suffer the consequences - lost data, which
                                                                     means, at best, lots of lost time and effort!
                                                                                        Care of Floppy Disks
                                                                     Common sense would say not to do anything that would
                                                                     physically damage the disk or that would erase the data. The
                                                                     following admonitions apply to all types of floppy disks.

                      Capacity of Disks
5¼” floppy - 360 KB or 1.2 MB
3½” floppy - 720 KB or 1.44 MB
                                                                           Heat                 Magnetism            Smoke, dust,
Hard disk - early ones = 20 MB - currently = 250+ GB where 1 GB
                                                                                                                     dirt, salt air
= 1 gigabyte = 1024 MB. The future - who knows!
Advances in technology for the read/write head and for the
densities on the disks are bringing larger and larger disk capaci-
ties for about the same price. In fact, you cannot find a small
capacity drive to buy, even if you wanted one! 120 GB drives are
plentiful and for the same price that we used to buy 1 Gig drives
(under $200). It’s enough to make you cry to think of what we
paid over the years and what we could get for those dollars
today. Ah, well. That’s the way the computer world works!
                                                                     Touch the mylar               Bend               Put weight on
                        Accessing Data                                                                                    Disk.
The process of accessing data has 4 steps.
1.    Seek
2.    Rotate
3.    Settle
4.    Data transfer
1. Seek (move the head to proper track). Measured as Seek
  Time (ms) .                                                                                      Spill on it
2. Rotate (rotate disk under the head to the correct sector).
     Measured as Rotational Delay (ms)
3. Settle (head lowers to disk; wait for vibrations from moving                           Using Floppy Disks
   to stop (actually touches only on floppies). Measured as          Improper preparation or use of a floppy disk can ruin your day,
 Settling Time (ms)                                                  and even your floppy drive. A few pointers are in order.
4. Data Transfer (copy data to main memory) Measured as
  Data Transfer Rate (kbs), where ms stands for millisecond =        Use standard computer disk labels. Note that some labels
  .001 second and kbs is kilobytes per second.                       wrap across the top as pictured at the right. Others fit entirely on
                                                                     the front of the disk.
Total time to transfer a kilobyte:
                                                                     Write on the label!! If your disks are not kept strictly at home,
* For floppies, 175 - 300 ms                                         every label should include your name and something about
* For hard drive, 15 - 80 ms                                         what’s on the disk. (On 5¼” disks, use a felt-tip marker only. A
* For new hard drives, .0146 ms (66.6 MB per sec) and higher..       pen or pencil can damage the disk inside.)
This is seriously fast!!
                                                                Page 24
Seal all edges down firmly. A loose corner might stick to the                                       Don’t
inside of the floppy drive, creating a major mess in there.
Put the label in the right spot. Don’t cover the holes in the
corners of 3½” floppies. Don’t stick to the metal slide .
Most important, insert the floppy right side up! The label goes
on top, the round metal part is on the bottom. The edge with the
metal slide goes in first.

                                                                     Jar the computer while the disk is spinning. Turn the computer
                                                                     off and quickly back on before spinning has stopped. Drop it -

                                                                                           Caring For Data
                                                                     Besides protecting the physical medium you are using to store
                                                                     data, you must also consider what you can do to safeguard the
                                                                     data itself. If the disk is kept from physical harm, but the data
                                                                     gets erased, you still have a major problem.
                                                                     So what can you do to safeguard the data on which you rely??
                                                                                             Write Protect
                    Care of Hard Disks                               This keeps your files from being overwritten with new ones.

 There are fewer precautions for hard disks since they are more      For floppies, you do this physically: 5¼” = cover the Write
protected by being sealed in air-tight cases. But when damage        Protect notch with tape and 3½” = open the Write Protect slide
does occur, it is a more serious matter. Larger amounts of data      For hard disks and CD-RW, make files Read-Only and/or Hidden
can be lost and hard disks are much, much more expensive that        to keep them from being overwritten. This is done by changing
floppy disks.                                                        the file attributes using whatever system you have for managing
Hard disks can have problems from magnetic fields and heat like      files.
floppies do, but these are very rare.                                                       Magnetic Tape
Most problems occur when the read/write head (looks like a
                                                                     Magnetic Tape uses a methoed similar to VCR tape for storing
pointer in the photo) damages the metal disk by hitting or even
just touching it. This is called a head crash.
                                                                     The speed of access can be quite slow, however, when the tape is
                                                                     long and what you want is not near the start. So this method is
                                                                     used primarily for major backups of large amounts of data.
                                                                     Businesses especially might do a backup of the day’s transac-
                                                                     tions every day and a backup of the whole system once a week
                                                                     or so. Keeping sets of backups like this minimizes the amount of
                                                                     data loss when the computer system goes down.
                                                                                             Types of Tape
                                                                     Each different tape storage system has its own requirements as
                                                                     to the size, the container type, and the magnetic characteristics of
                                                                     the tape. Older systems designed for networks use reel-to-reel
When the computer is on, the hard disk is                            tapes. Newer systems use cassettes. Some of these are even
spinning extremely fast. Any contact at all                          smaller than an audio cassette but hold more data that the huge
can cause pits or scratches. Every scratch or                        reels. Even if they look alike, the magnetic characteristics of tapes
pit is lost data. Damage in the root directory                       can vary. It is important to use the tape that is right for the
turns the whole hard disk into a lovely                              system.
doorstop! It’s completely dead.                                                      Tape Reel Tape Cassette
So the goal here is to keep that read/write head where it belongs,   Just as floppy disks and hard disks have several different
just barely above the hard disk, but never, ever touching it.        formats, so do magnetic tapes. The format method will determine
                                                                     the following characteristics.
                                                                 Page 25
                              Density                                    What you need for backup storage of changing data are
                                                                         rewritable disks. These use a different material for the laser to
Characteristic: Higher density means more data on shorter tape -
                                                                         work on that can be softened and lasered again.
Measured as bpi = bits per inch. Rranges from 800 bpi up to 6250
bpi. Looks like:                                                                                    Advantages
                                                                         1. The optical disk is much sturdier than the other media
                                                                            discussed so far. It is physically harder to break or melt or
                                                                         2. It is not sensitive to being touched, though it can get too dirty
                                                                            or scratched to be read.
                                                                         3. It is entirely unaffected by magnetic fields.
The tape is divided into logical blocks, as a floppy is divided into
                                                                         Plus you can imprint a pretty label right on the disk!
tracks and sectors. One file could take up many logical blocks,
but must take up one whole block at least. So smaller blocks             So for software providers, the optical disk is a great way to store
would result in more room for data. Looks like:                          the software and data that they want to distribute or sell.
                                Gap                                                             Other Devices
Two kinds of blank spots, called gaps, are set on the tape.              Invention springs eternal in the computer industry. So more and
* Interblock gap which separates logical blocks.                         different devices are brought out all the time, especially for
* Interrecord gap which is wider and separates records.                  special uses.

Notice the two size lines cutting across the tape in the picture         The history of computing suggests that some new technology
above. Smaller gaps would allow more data to be stored on the            will take over the market in the near future. Guessing which one
same size tape.                                                          will win the race is what makes fortunes in the stock market.

                        Optical Discs                                                            Flash Memory

An entirely different method of recording data is used for optical
                                                                         Several different brands of removable storage cards, also called
                                                                         memory cards, are now available. These are solid-state devices
You may guess from the word “optical” that it has to do with             (no moving parts) that read and write data electrically, instead of
light. You’d be exactly right!                                           magnetically.
To make an optical disk, tiny lasers create peaks and valleys in a       Devices like digital cameras, digital camcorders, and cell phones
plastic layer on a circular disk. In the device that reads the optical   Juneuse CompactFlash, SmartMedia, or another flash memory
disk these peaks and valleys are read as 1’s and 0’s by shining          card.
another laser on the disk.
                                                                         Laptop computers use PCMCIA cards, another type of flash
                 The most common size of optical disk is the CD-         memory, as solid-state hard disks.
                 ROM, which stands for Compact Disk - Read
                                                                                                   Flash drive
                 Only Memory. It looks just like an audio CD.
                 Almost all software is being distributed on CDs
                 now. The price of the drives that read the disks
                 (but can’t write one) has dropped low enough
                 that a new system will come with a CD drive
unless you go to some effort to avoid it! Such drives will also
play your audio CDs, if you have a sound card and speakers.
The CDs that contain commercial software are of the Write Once
Read Many (WORM) variety. They can’t be changed once they                This new type of flash memory storage device does not yet have
are created. This is where the ROM part comes from.                      a generally accepted name. Each company calls it something
                                                                         different, including flash pen, thumb drive, key drive, and mini-
The CD-ROM is useful as a backup medium only when you really             USB drive.
need indefinite storage of non-changing material. For data that
changes often it is too expensive since a disk can only be used          All are small, about the size of your thumb or car key, and plug
once.                                                                    into a USB port on the computer. No drivers are needed for
                                                                         Windows XP, 2000, or Me. Plug it in and the computer reports a
                                                                         new hard drive!
                                                              Page 26
Such small flash drives can have storage capacities, from 8 to 256    system of relays and satellites to tell a computer on Mars how to
MB! Much better than a floppy disk!                                   drive around without hitting the rocks.
Some flash drives include password protection and the ability to      Depending on the context, for computer communications you
run software right off the USB drive.                                 might use the terms:
                  Removable hard drives                               Data Communications for transmission of data and information
                                                                       over a communications channel
                                                                      Telecommunications for any long-distance communications,
                                                                       especially television
                                                                      Teleprocessing for accessing computer files located elsewhere
                                                                      A communications channel, also called a communications line or
                                                                      link, is the path that the data follows as it is transmitted from one
Several types of special drives that compress data are available.     computer to another. Below is an animation of a communications
A regular external hard drive can be used for backup, too.            channel at work. A PC is sending a message to a host computer
                                                                      clear across the country. Notice the variety of transmission
The image above is of an external Zip drive with a disk sticking      methods used: telephone lines, satellite links, microwave relay.
out.                                                                  This is a simplified version of what really goes on! (The anima-
                        Optical cards                                 tion runs 10 times and stops. To restart it, use your browser’s
                                                                      Refresh command.)
A chip on the card holds information like health records and auto
repair records. They can hold more data than the smart cards          With such complex communications channels, we need to be
since they don’t need to do any processing.                           aware of the capabilities and limitations of the various media in
                        Mass storage
                                                                      Transmission media just means the physical materials that are
Businesses with very large sets of data that need easy access         used to transmit data between computers.
use sets of cartridges with robot arms to pull out the right one on
command.                                                                                             Cable

                         Smart cards                                  For communications between computers that are linked by cable,
                                                                      there are three choices.
                                                                                        Twisted wire (phone line)

                                                                      Advantage: Easy to string, Cheap
A chip on the card itself tracks changes, like deducting pur-         Disadvantage: Subject to interference = static and garble
chases from the amount entered originally on the card. Smart
cards are already used in Europe and at colleges instead of using              Coaxial cable (round insulated wire)
a handful of coins at vending machines and at laundromats.
Another use involves a new sensor technology which lets a
smart card read your fingerprint right on the card. The digital
image of the fingerprint is then transmitted to a database to         Advantage: Not susceptible to interference, Transmits faster
compare it with the one on file for that card. You can prove you      Disadvantage: Heavy & bulky, Needs booster over distance
are really you!!
                                                                                   Fiber optic line (glass fibers)
                                        Computer communication
                                        is the transmission of
                                        data and information          Advantage: Smaller, Lighter, Faster (speed of light!), No
                                        over a communications          interference
                                        channel between two           Disadvantage: Expensive, Harder to install and modify
                                        computers, which can
                                        be several different                                     Broadcast
                                                                      For longer distances or when cables are not practical, other
                                                                      transmission media come into play. We’re getting really high tech
Communications between computers can be as simple as cabling
two computers to the same printer. It can be as complex as a
computer at NASA sending messages through an elaborate
                                                                  Page 27
It may seem odd to call microwaves, radio waves, or light a             An analog signal uses variations (modulations) in a signal to
“physical” medium. All are electromagnetic in nature. Sometimes         convey information. It is particularly useful for wave data like
they are treated by scientists like streams of teeny, tiny particles    sound waves. Analog signals are what your normal phone line
and other times like waves on the beach. In their “particle” life,      and sound speakers use.
they do behave like a bunch of physical particles. So it’s not
quite as odd as it first appears. (But all those electromagnetic
things are plenty odd!)
           Wireless (infrared, light, radio)

                                                                        Often communications between computers use the telephone
                                                                        system for at least part of the channel. A device is needed to
                                                                        translate between the analog phone line and the digital com-
                                                                        puter. Such a device is the modem, which comes from Modulate/
                                                                        Demodulate, which is what a modem does. It modulates a digital
                                                                        signal from the computer into an analog one to send data out
Advantage: Flexible, Portable
                                                                        over the phone line. Then for an incoming signal it demodulates
Disadvantage: Slower, Subject to interference
                                                                        the analog signal into a digital one.

                                                                        Though rather small, modems are very complex devices. There
                                                                        are entirely too many commands, protocols, and configuration
                                                                        choices available. Once you get a modem set up and working
                                                                        right the first time, you probably won’t have to tinker with it
                                                                        much afterwards.
Advantage: Speed of light, Uses a few sites
Disadvantage: Line-of-sight only                                                             Transmission Rate
                             Satellite                                  Confusion abounds when it comes to measuring the transmis-
                                                                        sion rate of a modem. Throughput is the term for the entire
                                                                        process - how much data is moved during a certain amount of
                                                                        time. Since the modem is only part of the process of moving
                                                                        data, getting a faster modem may not speed up your data
                                                                        There are two different parts of the data transfer to measure: the
                                                                        digital process and the analog process.
Advantage: Always in sight                                                                           Digital
Disadvantage: Expensive uplink and downlink facilities
                                                                        The rate of digital transmission is measured in bits per second
                              Signals                                   (bps). Common rates for regular modems are 28.8 Kbps, 33.6
                                                                        Kbps, and 56 Kbps where the K stands for thousand. Com-
Two types of signals are used for data transmission:
                                                                        pletely digital devices (discussed below) are much faster. Faster
                       Digital and Analog                               is better, of course. 2400 bps would send a 20-page single-
                                                                        spaced report in 5 min. (This is SLOW!!)
                                                                        The analog side is measured in baud where 1 baud is one change
                                                                        in the signal per second. Most people use bps and baud as
                                                                        though they were the same. For speeds of 2400 bps and under,
                                                                        this is true, but is it not so for the higher speeds where more
                                                                        than one bit is transmitted per signal change.
A digital signal is a stream of 0’s and 1’s. So this type is particu-
larly appropriate for computers to use.
                                                                 Page 28
                         Physical types                                  Normally a digital modem can receive data at a much higher rate
                                                                         than it can send it out. That works out fine for most people
There are three physical types of modems:
                                                                         because they are only sending out a few responses instead of
                              External                                   whole web pages or data files.
                                                                         Warning: Once you have used a high speed device, you will be
                                                                         spoiled forever!
                                                                                         Types of Digital Modems
                                                                                                   ISDN modem
External plugs into a serial port on the back of the computer            (Integrated Services Digital Network) - a digital device using a
                                                                         digital phone line. It actually should be called a terminal adapter,
Advantages: Can be moved to a different computer easily. Does
                                                                         but the name modem has stuck. An ISDN device is capable of
 not take up a slot inside the computer. Lights on front are
                                                                         higher rates than an normal modem, 64 Kbps for a single line and
 visible to show what the modem is doing.
                                                                         128 Kbps for a bonded dual line. ISDN adapters cost more than
Disadvantages: Takes up deskspace. Adds more cables to the
                                                                         normal modems and also require special arrangements with the
                                                                         phone company (and more $$ for them, of course!).
                                                                         Fiber optic line is best for the highest ISDN transmission rate,
                                                                         but the copper wires used in most homes and offices will work
                                                                         Note: To get the highest speeds out of your ISDN modem,
                                                                         you’ll need a high speed I/O (input/output) card in the computer
                                                                         to which to connect the modem.
                                                                                                   Cable modem
The phone line plugs directly into card through the back of the
computer                                                                 Hooks up to your cable TV line and can receive up to 1.5 Mbps.
                                                                         You must have cable TV service with a cable company that also
Advantages: Saves deskspace, Saves a cable.                              provides data service. You will need a special cable box to which
Disadvantages: Requires an internal peripheral slot. (They get           you connect your TV and your computer. You will be sharing the
 filled up.) Must use software display to see the lights that show       line with all of the cable customers hooked up to your particular
 what the modem is doing.                                                cable line. The actual transfer rate you get will depend on how
                            Acoustical                                   many people are using the cable at the same time. Once cable
                                                                         modems become popular in your neighborhood, your speed will
                                                                         slow down noticeably. It will probably still be faster than ISDN.
                                                                         (Asymmetric Digital Subscriber Line) - a new technology that
where the telephone handset is placed into the device, which is          allows a single regular telephone line to serve for normal phone
connected to the computer (Old technology! Not many of these             calls and digital data at the same time. An ADSL modem receives
around any more.)                                                        data at rates ranging from 384 Kbps to 8Mbps, depending on the
                                                                         particular kind of service. Even the slowest type is 4 times faster
Advantages: Can use a phone without having to move the
                                                                         than the best ISDN! Besides great speed, ADSL does not require
 phone wire.
                                                                         a separate phone line and you are connected all of the time. No
Disadvantages: Bulky, Connection much more prone to static
                                                                         more dialing up!
and interference, Only a standard handset will fit.
                                                                         You can use a regular phone on the same line and at the same
                       Digital Modems                                    time that you are surfing the Internet. No more busy signals to
A digital modem does not have to convert between analog and              your friends and relatives! Another plus is that you can easily
digital signals. Technically it’s not a “modem” at all since it is not   hook up all of the new parts yourself. This saves a LOT of
modulating and demodulating. A digital modem is faster than an           aggravation since you won’t have to wait on the phone company
analog modem.                                                            or the cable TV guy to show up.

To get the increase in speed you will have to pay extra (of                            How Device Speeds Compare
course!). Digital modems are more expensive and so are digital           The table below will help you see just how much faster the
data lines from the phone company. The phone company has to              different transfer rates are. To read the table, look at the speed in
install additional equipment for some kinds of digital modems.           the top row, which is in kilobytes per second. Below it you will
                                                                         see how long it takes to transfer 1 MB, 10 MB, and 1000 MB at
                                                                         that speed. Check out the last row. This one really shows the
                                                                Page 29
difference between analog modems and the digital kind. The                                    File Transfer
times go down from days to hours or even minutes!
                                                                     One of the most common uses of computer to computer commu-
Remember that just because your device is able to send and           nications is to transfer files from one to the other.
receive at a certain rate does not mean that it will ever actually
work that fast. There are many other factors in the communica-                                                 Downloading
tions channel that can reduce the transmission speed from the                                      Means to transfer a file to your
maximum.                                                                                           computer from elsewhere.

                                                                                                  Means to transfer a file from your
                                                                                                  computer to another.

                            Protocols                                                             Programs that manage this process
                                                                                                  include many file management
To talk to each other, modems have to exchange a good bit of
                                                                     features. You need to be able to see what files are available, their
information, since there are so many different types and speeds
                                                                     sizes, and the folders you can put the transferred file in. You may
of modems around. That’s what the high pitched squeals and
                                                                     want to rename the file or create a new folder for your new file.
squawks are that you can hear when an analog modem is trying
to connect. It’s modem talk for “So, who are you? Do you speak       Such a program will also handle the process of connecting to the
my language? Well, maybe we can find a common language so            other computer. Many of the names of these programs include
these guys can get connected.”                                       the letters FTP, which stands for File Transfer Protocol. (Yes,
                                                                     another kind of protocol. And there are more!!)
A digital modem does not make noises (an advantage!) but it
must do the same kind of negotiation with the device at the other                          Terminal Emulation
end to come up with a common language, called a protocol.
                                                                     Programs running on a network or that connect to a computer
A protocol defines what information is exchanged and in what         bulletin board (BBS), make an assumption about what kind of
order. The names of the protocols are of the form v.##. So you’ll    keyboard is being used. Keyboards for terminals used on
see things like v.25bis, v.34, and v.120. Some protocols are more    networks often have assigned special functions to certain keys.
stable or faster than others at certain tasks.                       They may even have keys that don’t exist on standard key-
                           Software                                  boards. In order to work with the network programs, you need a
                                                                     program that will disguise your keyboard and make the network
You can’t just hook up your computer to a network or a modem         think that you are one of them! You must emulate, that is mimic,
and start sending and receiving data. The computer needs             the keyboard that is expected.
instructions on how to do this. You need some kind of communi-
                                                                     A terminal emulation program will make:
cations software. Since there are a number of different communi-
cations tasks, there are different kinds of programs that manage
those tasks. Computer to Computer

                                                                               look like                  to the network or BBS.
                                                                                            Data Encryption
Dialing software tells the computer how to place a call on the
phone line connected to it. It also displays messages about the
progress of the call or lack thereof. A list of phone numbers for
frequently called, or frequently forgotten, numbers is an impor-
tant feature. These capabilities are often included in other
software packages.
                                                               Page 30
When sending data over a communications channel, there is                               Network Configuration
always the possibility that someone will see your data that you
didn’t mean to. If your data is of a sensitive nature, like your       There are a number of ways that computers can be connected
credit card number, or if it is secret, like the formula for Coca-     together to form networks.
Cola, you’d probably like to keep strangers from reading it.           The pattern of connections depends in part on the distances
A data encryption program encodes your data, just like spies do.       involved since that determines what hardware must be used. It
So to read it, a person would need the right decoding program          also depends on the degree of stability needed for the network.
and the right password or file to give that program so it would        That is, how important is it that the whole system can’t crash at
know what to do exactly.                                               the same time. These choices carry dollar costs, too. Better costs
                                                                       more, sometimes a LOT more.
                                   A network is a set of computers
                                   which are linked together on a      Each device in the network, whether it’s a computer, printer,
                                   permanent basis. This can           scanner, or whatever, is called a node.
                                   mean two computers cabled                                         Star
                                   together on the same desk, or
                                   thousands of computers across       The star pattern connects everything to one host, which is the
                                   the world.                          computer that handles the network tasks and holds the data. All
                                                                       communications between computers go through the host. This
                                                                       configuration is good for businesses that have large amounts of
                                                                       rapidly changing data, like banks and airline reservation offices.
                                                                       Advantages: Gives close control of data. Each PC sees all the
Advantages: Enables users to share hardware like scanners and            data. User sees up-to-date data always. If a computer other
 printers. This reduces costs by reducing the number of hard           than
 ware items bought.                                                      the host fails, no other computer is affected.
 Allows users access to data stored on others’ computers. This         Disadvantages: If host computer or its software goes down, the
 keeps everyone up-to-date on the latest data, since it’s all in the     whole network is down. (A backup computer system would be
 same file, rather than having to make copies of the files, which        necessary to keep going while repairs are made.)
 are immediately out-of-date.                                                                         Bus
 Can even let users run programs that are not installed on their
 own computers but are installed elsewhere in the network. This
 reduces the effort for networks administrators to keep pro
 grams configured correctly and saves a lot of storage space.
Disadvantages: Accessing anything across a network is slower
 than accessing your own computer.
 More complexity adds new problems to handle.                          The bus pattern connects the computer to the same communica-
 Less customization is possible for shared programs and folders.       tions line. Communications goes both directions along the line.
 Everyone will have to follow the same conventions for storing         All the computers can communicate with each other without
 and naming files so others can find the right files.                  having to go through the server.

 Sharing is hard for some folks!                                       Advantages: Any one computer or device being down does not
                                                                        affect the others.
                               LAN                                     Disadvantages: Can’t connect a large number of computers this
A LAN is a Local Area Network. This would include networks              way. It’s physically difficult to run the one communications line
where the computers are relatively close together. So LANs              over a whole building, for example.
would be within the same office, a single building, or several                                       Ring
buildings close together.
The graphic at the right shows two buildings with 4 departments
connected as a LAN.
A WAN is a Wide Area Network, which would be all networks
too large to be LANs. There doesn’t seem to be a clear line
between the two designations. A WAN would be most useful for
large companies with offices or factories in widely separated
areas, like Microsoft, IBM, Ford, AT&T, etc.
                                                                Page 31
The ring pattern connects the computers and other devices one           need to communicate with each other, but only sometimes. It
to the other in a circle. here is no central host computer that         would be easier and cheaper to connect them to each other than
holds all the data. Communication flows in one direction around         to put them all on the same larger network. The best arrangement
the ring. This configuration is good when the processing of data        would be for the departmental networks to be of the same kind so
can be done on the local PC.                                            that a bridge could be used.
Advantages: Requires less cabling and so is less expensive.
Disadvantages: If one node goes down, it takes down the whole                      Good Boot Guide to Your
network.                                                                             Operating Systems
In the token ring form of a ring network, a token is constantly
passed along the network. A device must wait until the token is at      If you have a computer, then you have heard about operating
that device.                                                            systems. Any desktop or laptop PC that you buy normally comes
                                                                        pre-loaded with Windows XP. Many corporate servers use the
 Then it can attach the message it wants to send to the token.          Linux or UNIX operating systems. The operating system (OS) is
When the token reaches the intended recipient device on the             the first thing loaded onto the computer - without the operating
network, it will release the message. The token circulates very         system, a computer is useless.
fast, but this obviously means that most of the time a device will
have to do some waiting before it can send out a message.               More recently, operating systems have started to pop up in
                                                                        smaller computers as well. If you like to tinker with electronic
                   Connecting Networks                                  devices, you are probably pleased that operating systems can
Networks can be connected to each other, too. There are                 now be found on many of the devices we use every day, from cell
difficulties in doing so, however. A combination of software and        phones to wireless access points. The computers used in these
hardware must be used to do the job.                                    little devices have gotten so powerful that they can now actually
                                                                        run an operating system and applications. The computer in a
                             Gateway                                    typical modern cell phone is now more powerful than a desktop
                                                                        computer from 20 years ago, so this progression makes sense
                                                                        and is a natural development. In any device that has an operating
                                                                        system, there’s usually a way to make changes to how the device
                                                                        works. This is far from a happy accident; one of the reasons
                                                                        operating systems are made out of portable code rather than
                                                                        permanent physical circuits is so that they can be changed or
                                                                        modified without having to scrap the whole device.
A Gateway connects networks of different kinds, like connecting
a network of PCs to a main frame network. This can be complex!

A Bridge connects networks of the same type. This job is simple.

                                                                        For a desktop computer user, this means you can add a new
                                                                        security update, system patch, new application or often even a
                                                                        new operating system entirely rather than junk your computer
                                                                        and start again with a new one when you need to make a change.
                                                                        As long as you understand how an operating system works and
A Router connects several networks. A router is smart enough to         know how to get at it, you can in many cases change some of the
pick the right path for communications traffic. If there is a partial   ways it behaves. And, it’s as true of your cell phone as it is of
failure of the network, a router looks for an alternate route.          your computer.
Suppose the accounting, advertising, and shipping departments           The purpose of an operating system is to organize and control
of a company each have networks of PCs. These departments               hardware and software so that the device it lives in behaves in a
                                                                 Page 32
flexible but predictable way. In this article, we’ll tell you what a   memory, storage and input/output (I/O) bandwidth for their own
piece of software must do to be called an operating system, show       purposes. In this capacity, the operating system plays the role of
you how the operating system in your desktop computer works            the good parent, making sure that each application gets the
and give you some examples of how to take control of the other         necessary resources while playing nicely with all the other
operating systems around you.                                          applications, as well as husbanding the limited capacity of the
                                                                       system to the greatest good of all the users and applications.
                      The Bare Bones
                                                                       The second task, providing a consistent application interface, is
                                                                       especially important if there is to be more than one of a particular
                                                                       type of computer using the operating system, or if the hardware
                                                                       making up the computer is ever open to change. A consistent
                                                                       application program interface (API) allows a software developer
                                                                       to write an application on one computer and have a high level of
                                                                       confidence that it will run on another computer of the same type,
                                                                       even if the amount of memory or the quantity of storage is
                                                                       different on the two machines.
                                                                       Even if a particular computer is unique, an operating system can
                                                                       ensure that applications continue to run when hardware up-
                                                                       grades and updates occur. This is because the operating system
Not all computers have operating systems. The computer that            and not the application is charged with managing the hardware
controls the microwave oven in your kitchen, for example,              and the distribution of its resources. One of the challenges facing
doesn’t need an operating system. It has one set of tasks to           developers is keeping their operating systems flexible enough to
perform, very straightforward input to expect (a numbered              run hardware from the thousands of vendors manufacturing
keypad and a few pre-set buttons) and simple, never-changing           computer equipment. Today’s systems can accommodate
hardware to control. For a computer like this, an operating system     thousands of different printers, disk drives and special peripher-
would be unnecessary baggage, driving up the development and           als in any possible combination.
manufacturing costs significantly and adding complexity where
none is required. Instead, the computer in a microwave oven                            What Kinds Are There?
simply runs a single hard-wired program all the time.                  Within the broad family of operating systems, there are generally
For other devices, an operating system creates the ability to:         four types, categorized based on the types of computers they
* serve a variety of purposes                                          control and the sort of applications they support. The broad
* interact with users in more complicated ways                         categories are:
* keep up with needs that change over time                             * Real-time operating system (RTOS) - Real-time operating
                                                                       systems are used to control machinery, scientific instruments and
All desktop computers have operating systems. The most
                                                                       industrial systems. An RTOS typically has very little user-
common are the Windows family of operating systems developed
                                                                       interface capability, and no end-user utilities, since the system
by Microsoft, the Macintosh operating systems developed by
                                                                       will be a “sealed box” when delivered for use. A very important
Apple and the UNIX family of operating systems (which have
                                                                       part of an RTOS is managing the resources of the computer so
been developed by a whole history of individuals, corporations
                                                                       that a particular operation executes in precisely the same amount
and collaborators). There are hundreds of other operating
                                                                       of time every time it occurs. In a complex machine, having a part
systems available for special-purpose applications, including
                                                                       move more quickly just because system resources are available
specializations for mainframes, robotics, manufacturing, real-time
                                                                       may be just as catastrophic as having it not move at all because
control systems and so on.
                                                                       the system is busy.
                   What Does It Do?                                    * Single-user, single task - As the name implies, this operating
At the simplest level, an operating system does two things:               system is designed to manage the computer so that one user
                                                                         can effectively do one thing at a time. The Palm OS for Palm
1. It manages the hardware and software resources of the system.
                                                                         handheld computers is a good example of a modern single-user,
    In a desktop computer, these resources include such things as
                                                                         single-task operating system.
   the processor, memory, disk space, etc. (On a cell phone, they
                                                                       * Single-user, multi-tasking - This is the type of operating
    include the keypad, the screen, the address book, the phone
                                                                          system most people use on their desktop and laptop comput-
   dialer, the battery and the network connection.)
                                                                         ers today. Microsoft’s Windows and Apple’s MacOS platforms
2. It provides a stable, consistent way for applications to deal
                                                                         are both examples of operating systems that will let a single
   with the hardware without having to know all the details of the
                                                                         user have several programs in operation at the same time. For
                                                                         example, it’s entirely possible for a Windows user to be writing
The first task, managing the hardware and software resources, is         a note in a word processor while downloading a file from the
very important, as various programs and input methods compete            Internet while printing the text of an e-mail message.
for the attention of the central processing unit (CPU) and demand
                                                              Page 33
* Multi-user - A multi-user operating system allows many              vendors do build many more utility programs and auxiliary
  different users to take advantage of the computer’s resources       functions into their operating systems, these six tasks define the
 simultaneously. The operating system must make sure that the         core of nearly all operating systems. Let’s look at the tools the
  requirements of the various users are balanced, and that each       operating system uses to perform each of these functions.
  of the programs they are using has sufficient and separate
  resources so that a problem with one user doesn’t affect the                        Processor Management
 entire community of users. Unix, VMS and mainframe operating         The heart of managing the processor comes down to two related
 systems, such as MVS, are examples of multi-user operating           issues:
  systems.                                                            * Ensuring that each process and application receives enough of
It’s important to differentiate here between multi-user operating       the processor’s time to function properly.
systems and single-user operating systems that support net-           * Using as many processor cycles for real work as is possible.
working. Windows 2000 and Novell Netware can each support             The basic unit of software that the operating system deals with in
hundreds or thousands of networked users, but the operating           scheduling the work done by the processor is either a process or
systems themselves aren’t true multi-user operating systems.          a thread, depending on the operating system.
The system administrator is the only “user” for Windows 2000 or
Netware. The network support and all of the remote user logins        It’s tempting to think of a process as an application, but that
the network enables are, in the overall plan of the operating         gives an incomplete picture of how processes relate to the
system, a program being run by the administrative user.               operating system and hardware. The application you see (word
                                                                      processor or spreadsheet or game) is, indeed, a process, but that
With the different types of operating systems in mind, it’s time to   application may cause several other processes to begin, for tasks
look at the basic functions provided by an operating system.          like communications with other devices or other computers.
                       Wake-Up Call                                   There are also numerous processes that run without giving you
                                                                      direct evidence that they ever exist. For example, Windows XP
When you turn on the power to a computer, the first program that      and UNIX can have dozens of background processes running to
runs is usually a set of instructions kept in the computer’s read-    handle the network, memory management, disk management,
only memory (ROM). This code examines the system hardware to          virus checking and so on.
make sure everything is functioning properly. This power-on self
test (POST) checks the CPU, memory, and basic input-output            A process, then, is software that performs some action and can
systems (BIOS) for errors and stores the result in a special          be controlled - by a user, by other applications or by the
memory location. Once the POST has successfully completed,            operating system.
the software loaded in ROM (sometimes called the BIOS or              It is processes, rather than applications, that the operating
firmware) will begin to activate the computer’s disk drives. In       system controls and schedules for execution by the CPU. In a
most modern computers, when the computer activates the hard           single-tasking system, the schedule is straightforward. The
disk drive, it finds the first piece of the operating system: the     operating system allows the application to begin running,
bootstrap loader.                                                     suspending the execution only long enough to deal with
The bootstrap loader is a small program that has a single             interrupts and user input.
function: It loads the operating system into memory and allows it     Interrupts are special signals sent by hardware or software to the
to begin operation. In the most basic form, the bootstrap loader      CPU. It’s as if some part of the computer suddenly raised its hand
sets up the small driver programs that interface with and control     to ask for the CPU’s attention in a lively meeting. Sometimes the
the various hardware subsystems of the computer. It sets up the       operating system will schedule the priority of processes so that
divisions of memory that hold the operating system, user              interrupts are masked — that is, the operating system will ignore
information and applications. It establishes the data structures      the interrupts from some sources so that a particular job can be
that will hold the myriad signals, flags and semaphores that are      finished as quickly as possible. There are some interrupts (such
used to communicate within and between the subsystems and             as those from error conditions or problems with memory) that are
applications of the computer. Then it turns control of the            so important that they can’t be ignored. These non-maskable
computer over to the operating system.                                interrupts (NMIs) must be dealt with immediately, regardless of
The operating system’s tasks, in the most general sense, fall into    the other tasks at hand.
six categories:                                                       While interrupts add some complication to the execution of
* Processor management                                                processes in a single-tasking system, the job of the operating
* Memory management                                                   system becomes much more complicated in a multi-tasking
* Device management                                                   system. Now, the operating system must arrange the execution of
* Storage management                                                  applications so that you believe that there are several things
* Application interface                                               happening at once. This is complicated because the CPU can
* User interface                                                      only do one thing at a time. In order to give the appearance of
                                                                      lots of things happening at the same time, the operating system
While there are some who argue that an operating system should
                                                                      has to switch between different processes thousands of times a
do more than these six tasks, and some operating-system
                                                                      second. Here’s how it happens:
                                                               Page 34
* A process occupies a certain amount of RAM. It also makes            This process swapping happens without direct user interference,
  use of registers, stacks and queues within the CPU and               and each process gets enough CPU cycles to accomplish its task
  operating-system memory space.                                       in a reasonable amount of time. Trouble can come, though, if the
* When two processes are multi-tasking, the operating system           user tries to have too many processes functioning at the same
  allots a certain number of CPU execution cycles to one program.      time. The operating system itself requires some CPU cycles to
* After that number of cycles, the operating system makes copies       perform the saving and swapping of all the registers, queues and
   of all the registers, stacks and queues used by the processes,      stacks of the application processes. If enough processes are
   and notes the point at which the process paused in its execu        started, and if the operating system hasn’t been carefully
  tion.                                                                designed, the system can begin to use the vast majority of its
* It then loads all the registers, stacks and queues used by the       available CPU cycles to swap between processes rather than run
  second process and allows it a certain number of CPU cycles.         processes. When this happens, it’s called thrashing, and it
* When those are complete, it makes copies of all the registers,       usually requires some sort of direct user intervention to stop
   stacks and queues used by the second program, and loads the         processes and bring order back to the system.
 first program.
                                                                       One way that operating-system designers reduce the chance of
                                                                       thrashing is by reducing the need for new processes to perform
                                                                       various tasks. Some operating systems allow for a “process-lite,”
                                                                       called a thread, that can deal with all the CPU-intensive work of a
                                                                       normal process, but generally does not deal with the various
                                                                       types of I/O and does not establish structures requiring the
                                                                       extensive process control block of a regular process. A process
                                                                       may start many threads or other processes, but a thread cannot
                                                                       start a process.
                                                                       So far, all the scheduling we’ve discussed has concerned a single
                                                                       CPU. In a system with two or more CPUs, the operating system
                                                                       must divide the workload among the CPUs, trying to balance the
                                                                       demands of the required processes with the available cycles on
                                                                       the different CPUs. Asymmetric operating systems use one
                                                                       CPU for their own needs and divide application processes among
                                                                       the remaining CPUs. Symmetric operating systems divide
                                                                       themselves among the various CPUs, balancing demand versus
                                                                       CPU availability even when the operating system itself is all
                                                                       that’s running. See Page 35 for Asymnetic and Symmetic Figures.
All of the information needed to keep track of a process when
switching is kept in a data package called a process control           Even if the operating system is the only software with execution
block. The process control block typically contains:                   needs, the CPU is not the only resource to be scheduled.
* An ID number that identifies the process                             Memory management is the next crucial step in making sure that
* Pointers to the locations in the program and its data where          all processes run smoothly.
  processing last occurred                                                     Memory Storage and Management
* Register contents
* States of various flags and switches                                 When an operating system manages the computer’s memory,
* Pointers to the upper and lower bounds of the memory required        there are two broad tasks to be accomplished:
  for the process                                                      1. Each process must have enough memory in which to execute,
* A list of files opened by the process                                   and it can neither run into the memory space of another
* The priority of the process                                             process nor be run into by another process.
* The status of all I/O devices needed by the process                  2. The different types of memory in the system must be used
                                                                          properly so that each process can run most effectively.
Each process has a status associated with it. Many processes
consume no CPU time until they get some sort of input. For             The first task requires the operating system to set up memory
example, a process might be waiting on a keystroke from the user.      boundaries for types of software and for individual applica-
While it is waiting for the keystroke, it uses no CPU time. While it   tions.
is waiting, it is “suspended”. When the keystroke arrives, the OS
changes its status. When the status of the process changes,
from pending to active, for example, or from suspended to
running, the information in the process control block must be
used like the data in any other program to direct execution of the
task-switching portion of the operating system.
                                                               Page 35
                                                                       given a chunk of memory that is a multiple of 2 kilobytes in size.
                                                                       Applications will be loaded in these fixed block sizes, with the
                                                                       blocks starting and ending on boundaries established by words
                                                                       of 4 or 8 bytes. These blocks and boundaries help to ensure that
                                                                       applications won’t be loaded on top of one another’s space by a
                                                                       poorly calculated bit or two. With that ensured, the larger
                                                                       question is what to do when the 500-kilobyte application space is
                                                                       In most computers, it’s possible to add memory beyond the
                                                                       original capacity. For example, you might expand RAM from 1 to
                                                                       2 megabytes. This works fine, but tends to be relatively expen-
                                                                       sive. It also ignores a fundamental fact of computing — most of
                                                                       the information that an application stores in memory is not being
                                                                       used at any given moment. A processor can only access memory
                                                                       one location at a time, so the vast majority of RAM is unused at
                                                                       any moment. Since disk space is cheap compared to RAM, then
                                                                       moving information in RAM to hard disk can greatly expand
                                                                       RAM space at no cost. This technique is called virtual memory
                                                                       Disk storage is only one of the memory types that must be
                                                                       managed by the operating system, and is the slowest. Ranked in
                                                                       order of speed, the types of memory in a computer system are:
                                                                       * High-speed cache - This is fast, relatively small amounts of
                                                                          memory that are available to the CPU through the fastest
                                                                          connections. Cache controllers predict which pieces of data
                                                                         the CPU will need next and pull it from main memory into high-
                                                                          speed cache to speed up system performance.
                                                                       * Main memory - This is the RAM that you see measured in
                                                                          megabytes when you buy a computer.
                                                                       * Secondary memory - This is most often some sort of rotating
                                                                          magnetic storage that keeps applications and data available to
                                                                          be used, and serves as virtual RAM under the control of the
                                                                          operating system.
                                                                       The operating system must balance the needs of the various
                                                                       processes with the availability of the different types of memory,
                                                                       moving data in blocks (called pages) between available memory
                                                                       as the schedule of processes dictates.
                                                                                          Device Management
                                                                       The path between the operating system and virtually all hardware
                                                                       not on the computer’s motherboard goes through a special
As an example, let’s look at an imaginary small system with 1
                                                                       program called a driver. Much of a driver’s function is to be the
megabyte (1,000 kilobytes) of RAM. During the boot process, the
                                                                       translator between the electrical signals of the hardware sub-
operating system of our imaginary computer is designed to go to
                                                                       systems and the high-level programming languages of the
the top of available memory and then “back up” far enough to
                                                                       operating system and application programs. Drivers take data
meet the needs of the operating system itself. Let’s say that the
                                                                       that the operating system has defined as a file and translate them
operating system needs 300 kilobytes to run. Now, the operating
                                                                       into streams of bits placed in specific locations on storage
system goes to the bottom of the pool of RAM and starts
                                                                       devices, or a series of laser pulses in a printer.
building up with the various driver software required to control
the hardware subsystems of the computer. In our imaginary              Because there are such wide differences in the hardware con-
computer, the drivers take up 200 kilobytes. So after getting the      trolled through drivers, there are differences in the way that the
operating system completely loaded, there are 500 kilobytes            driver programs function, but most are run when the device is
remaining for application processes.                                   required, and function much the same as any other process. The
                                                                       operating system will frequently assign high-priority blocks to
When applications begin to be loaded into memory, they are
                                                                       drivers so that the hardware resource can be released and readied
loaded in block sizes determined by the operating system. If the
                                                                       for further use as quickly as possible.
block size is 2 kilobytes, then every process that is loaded will be
                                                                 Page 36
One reason that drivers are separate from the operating system is        that grows as data is added but does not shrink when data is
so that new functions can be added to the driver - and thus to           removed). Now, let’s look at what the operating system does to
the hardware subsystems - without requiring the operating                turn the instruction into action.
system itself to be modified, recompiled and redistributed.
                                                                         The operating system sends a query to the disk drive to get the
Through the development of new hardware device drivers,
                                                                         location of the first available free storage location.
development often performed or paid for by the manufacturer of
the subsystems rather than the publisher of the operating                With that information, the operating system creates an entry in
system, input/output capabilities of the overall system can be           the file system showing the beginning and ending locations of
greatly enhanced.                                                        the file, the name of the file, the file type, whether the file has
                                                                         been archived, which users have permission to look at or modify
Managing input and output is largely a matter of managing
                                                                         the fil, and the date and time of the file’s creation.
queues and buffers, special storage facilities that take a stream
of bits from a device, perhaps a keyboard or a serial port, hold         The operating system writes information at the beginning of the
those bits, and release them to the CPU at a rate slow enough for        file that identifies the file, sets up the type of access possible and
the CPU to cope with. This function is especially important when         includes other information that ties the file to the application. In
a number of processes are running and taking up processor time.          all of this information, the queries to the disk drive and addresses
The operating system will instruct a buffer to continue taking           of the beginning and ending point of the file are in formats
input from the device, but to stop sending data to the CPU while         heavily dependent on the manufacturer and model of the disk
the process using the input is suspended. Then, when the                 drive.
process needing input is made active once again, the operating
                                                                         Because the programmer has written the program to use the API
system will command the buffer to send data. This process
                                                                         for disk storage, the programmer doesn’t have to keep up with
allows a keyboard or a modem to deal with external users or
                                                                         the instruction codes, data types and response codes for every
computers at a high speed even though there are times when the
                                                                         possible hard disk and tape drive. The operating system,
CPU can’t use input from those sources.
                                                                         connected to drivers for the various hardware subsystems, deals
Managing all the resources of the computer system is a large part        with the changing details of the hardware - the programmer must
of the operating system’s function and, in the case of real-time         simply write code for the API and trust the operating system to
operating systems, may be virtually all the functionality required.      do the rest.
For other operating systems, though, providing a relatively
                                                                         APIs have become one of the most hotly contested areas of the
simple, consistent way for applications and humans to use the
                                                                         computer industry in recent years. Companies realize that
power of the hardware is a crucial part of their reason for              programmers using their API will ultimately translate this into the
existing.                                                                ability to control and profit from a particular part of the industry.
                                                                         This is one of the reasons that so many companies have been
                Interface to the World                                   willing to provide applications like readers or viewers to the
                   Application Interface                                 public at no charge. They know consumers will request that
                                                                         programs take advantage of the free readers, and application
Just as drivers provide a way for applications to make use of            companies will be ready to pay royalties to allow their software to
hardware subsystems without having to know every detail of the           provide the functions requested by the consumers.
hardware’s operation, application program interfaces (APIs) let
application programmers use functions of the computer and                                        User Interface
operating system without having to directly keep track of all the        Just as the API provides a consistent way for applications to use
details in the CPU’s operation. Let’s look at the example of             the resources of the computer system, a user interface (UI)
creating a hard disk file for holding data to see why this can be        brings structure to the interaction between a user and the
important.                                                               computer. In the last decade, almost all development in user
A programmer writing an application to record data from a                interfaces has been in the area of the graphical user interface
scientific instrument might want to allow the scientist to specify       (GUI), with two models, Apple’s Macintosh and Microsoft’s
the name of the file created. The operating system might provide         Windows, receiving most of the attention and gaining most of
an API function named MakeFile for creating files. When writing          the market share. The popular, open-source Linux operating
the program, the programmer would insert a line that looks like          system also supports a graphical user interface.
this:                                                                    There are other user interfaces, some graphical and some not, for
                   MakeFile [1, %Name, 2]                                other operating systems.
In this example, the instruction tells the operating system to           Unix, for example, has user interfaces called shells that present a
create a file that will allow random access to its data (signified by    user interface more flexible and powerful than the standard
the 1 - the other option might be 0 for a serial file), will have a      operating system text-based interface. Programs such as the
name typed in by the user (%Name) and will be a size that varies         Korn Shell and the C Shell are text-based interfaces that add
depending on how much data is stored in the file (signified by           important utilities, but their main purpose is to make it easier for
the 2 - other options might be zero for a fixed size, and 1 for a file   the user to manipulate the functions of the operating system.
                                                               Page 37
There are also graphical user interfaces, such as X-Windows and         Open source requires the distribution of original source materials
Gnome, that make Unix and Linux more like Windows and                  that can be studied, altered and built upon, with the results once
Macintosh computers from the user’s point of view.                     again freely distributed. In the desktop computer realm, this has
                                                                       led to the development and distribution of countless useful and
It’s important to remember that in all of these examples, the user
                                                                       cost-free applications like the image manipulation program GIMP
interface is a program or set of programs that sits as a layer
                                                                       and the popular web server Apache. In the consumer device
above the operating system itself. The same thing is true, with
                                                                       realm, the use of Linux has paved the way for individual users to
somewhat different mechanisms, of both Windows and
                                                                       have greater control over how their devices behave.
Macintosh operating systems. The core operating-system
functions - the management of the computer system - lie in the                             Getting at the OS
kernel of the operating system. The display manager is separate,
                                                                       Many consumer devices like cell phones and routers deliberately
though it may be tied tightly to the kernel beneath. The ties
                                                                       hide access to the operating system from the user, mostly to
between the operating-system kernel and the user interface,
                                                                       make sure that it’s not inadvertently broken or removed. In many
utilities and other software define many of the differences in
                                                                       cases, they leave open a “developer’s mode” or “programmer’s
operating systems today, and will further define them in the
                                                                       mode” which allow changes to be made if you know how to find
                                                                       it. Often these systems may be programmed in such a way that
                        What’s New                                     there are only a limited range of changes that can be made. But
                                                                       some devices leave open both a mode of access and the means
              The Growing Importance of Networks
                                                                       of making powerful changes, especially those that use Linux.
For desktop systems, access to a LAN or the Internet has               Here are a couple of examples:
become such an expected feature that in many ways it’s hard to
                                                                       * The TiVo DVR runs on a modified version of Linux. All of the
discuss an operating system without making reference to its
                                                                         modifications are public knowledge, and can be downloaded
connections to other computers and servers. Operating system
                                                                         here along with some special tools for manipulating the code.
developers have made the Internet the standard method for
                                                                         Many enterprising TiVo users have done just that, adding
delivering crucial operating system updates and bug fixes.
                                                                         functionality to their systems, from increasing the storage
Although it is possible to receive these updates via CD, it is
                                                                         capacity to getting to UNIX shells to changing the mode from
becoming increasingly less common. In fact, some entire operat-
                                                                         NTSC to PAL. Here’s a FAQ on how to hack your TiVo.
ing systems themselves are only available through distribution
over the Internet.
Further, a process called NetBooting has streamlined the
capability to move the working operating system of a standard
consumer desktop computer - kernel, user interface and all - off of
the machine it controls. This was previously only possible for
experienced power-users on multi-user platforms like UNIX and
with a suite of specialized applications. NetBooting allows the        Philips HDR312 TiVo 30-Hour Digital Video Recorder and
operating system for one computer to be served over a network          Linksys EZXS55W EtherFast 10/100 5-Port Workgroup Switch
connection, by a remote computer connected anywhere in the
                                                                       * Many home routers also run on Linux, including those made by
network. One NetBoot server can serve operating systems to
                                                                         Linksys. This article from G4TechTV discusses how to hack
several dozen client computers simultaneously, and to the user
                                                                         your Linksys Router and take control of the Linux inside.
sitting in front of each client computer the experience is just like

                                                                                  Good Boot Guide to Your
they are using their familiar desktop operating system like
Windows or MacOS.
                         Open Source
One question concerning the future of operating systems                The computer you are using to read this page uses a micropro-
revolves around the ability of a particular philosophy of software     cessor to do its work. The microprocessor is the heart of any
distribution to create an operating system useable by corpora-         normal computer, whether it is a desktop machine, a server or a
tions and consumers together.                                          laptop. The microprocessor you are using might be a Pentium, a
                                                                       K6, a PowerPC, a Sparc or any of the many other brands and
Linux, the operating system created and
                                                                       types of microprocessors, but they all do approximately the same
distributed according to the principles of
                                                                       thing in approximately the same way.
open source, has had a significant impact
on the operating system in general. Most                               If you have ever wondered what the microprocessor in your
operating systems, drivers and utility                                 computer is doing, or if you have ever wondered about the
programs are written by commercial organi-                             differences between types of microprocessors, then read on. In
zations that distribute executable versions                            this article, you will learn how fairly simple digital logic tech-
of their software - versions that can’t be                             niques allow a computer to do its job, whether its playing a game
studied or altered.                                                    or spell checking a document!
                                                              Page 38
                                                                     improvements on the basic design of the 8088. The Pentium 4 can
                                                                     execute any piece of code that ran on the original 8088, but it
                                                                     does it about 5,000 times faster!
                                                                               Microprocessor Progression: Intel
                                                                     The following table helps you to understand the differences
                                                                     between the different processors that Intel has introduced over
                                                                     the years.
                                                                     Name        Date Transistors Microns Clock speed Data   MIPS
                                                                     8080       1974   6,000        6       2 MHz     8 bits   0.64
                                                                     8088       1979   29,000       3       5 MHz    16 bits   0.33
                                                                                                                     8-bit bus
                                                                     80286      1982   134,000      1.5     6 MHz    16 bits     1
                                                                     80386      1985   275,000      1.5     16 MHz 32 bits       5

                Microprocessor History                               80486      1989   1,200,000     1      25 MHz 32 bits      20
                                                                     Pentium    1993   3,100,000    0.8    60 MHz    32 bits    100
                                                                                                                     64-bit bus
                                                                     Pentium II 1997   7,500,000    0.35    233 MHz 32 bits    ~300
                                                                                                                    64-bit bus
                                                                     Pentium 3 1999    9,500,000    0.25    450 MHz 32 bits    ~510
                                                                                                                    64-bit bus
                                                                     Pentium 4 2000    42,000,000   0.18    1.5 GHz 32 bits ~1700
                                                                                                                    64-bit bus

                      Intel 4004 chip
                                                                                           What’s a Chip?
A microprocessor - also known as a CPU or central processing
unit - is a complete computation engine that is fabricated on a       A chip is also called an integrated circuit. Generally it is a
single chip. The first microprocessor was the Intel 4004, intro-      small, thin piece of silicon onto which the transistors
duced in 1971. The 4004 was not very powerful — all it could do       making up the microprocessor have been etched. A chip might
was add and subtract, and it could only do that 4 bits at a time.     be as large as an inch on a side and can contain tens of
                                                                      millions of transistors. Simpler processors might consist of
But it was amazing that everything was on one chip. Prior to the
                                                                      a few thousand transistors etched onto a chip just a few
4004, engineers built computers either from collections of chips
                                                                      millimeters square.
or from discrete components (transistors wired one at a time).
The 4004 powered one of the first portable electronic calculators.
                                                                     Information about this table:
                                                                     * The date is the year that the processor was first introduced.
                                                                        Many processors are re-introduced at higher clock speeds for
                                                                       many years after the original release date.
                                                                     * Transistors is the number of transistors on the chip. You can
                                                                        see that the number of transistors on a single chip has risen
                                                                        steadily over the years.
                                                                     * Microns is the width, in microns, of the smallest wire on the
                                                                       chip. For comparison, a human hair is 100 microns thick. As
                         Intel 8080                                     the feature size on the chip goes down, the number of transis-
                                                                        tors rises.
The first microprocessor to make it into a home computer was the     * Clock speed is the maximum rate that the chip can be clocked
Intel 8080, a complete 8-bit computer on one chip, introduced in       at. Clock speed will make more sense in the next section.
1974. The first microprocessor to make a real splash in the market   * Data Width is the width of the ALU. An 8-bit ALU can add/
was the Intel 8088, introduced in 1979 and incorporated into the       subtract/multiply/etc. two 8-bit numbers, while a 32-bit ALU
IBM PC (which first appeared around 1982). If you are familiar         can manipulate 32-bit numbers. An 8-bit ALU would have to
with the PC market and its history, you know that the PC market        execute four instructions to add two 32-bit numbers, while a
moved from the 8088 to the 80286 to the 80386 to the 80486 to the      32-bit ALU can do it in one instruction. In many cases, the
Pentium to the Pentium II to the Pentium III to the Pentium 4. All     external data bus is the same width as the ALU, but not
of these microprocessors are made by Intel and all of them are         always.
                                                                Page 39
  The 8088 had a 16-bit ALU and an 8-bit bus, while the
  modern Pentiums fetch data 64 bits at a time for their 32-bit
* MIPS stands for “millions of instructions per second” and is a
  rough measure of the performance of a CPU. Modern CPUs
  can do so many different things that MIPS ratings lose a lot of
  their meaning, but you can get a general sense of the relative
  power of the CPUs from this column.
From this table you can see that, in general, there is a relationship
between clock speed and MIPS. The maximum clock speed is a
function of the manufacturing process and delays within the
chip. There is also a relationship between the number of transis-
tors and MIPS. For example, the 8088 clocked at 5 MHz but only
executed at 0.33 MIPS (about one instruction per 15 clock
cycles). Modern processors can often execute at a rate of two
instructions per clock cycle. That improvement is directly related
to the number of transistors on the chip and will make more sense
in the next section.
                Inside a Microprocessor

                                                                        This is about as simple as a microprocessor gets. This micropro-
                                                                        cessor has:
                                                                        An address bus (that may be 8, 16 or 32 bits wide) that sends
                                                                          an address to memory
                                                                        A data bus (that may be 8, 16 or 32 bits wide) that can send
                                                                          data to memory or receive data from memory
                                                                        An RD (read) and WR (write) line to tell the memory whether it
                                                                           wants to set or get the addressed location
                                                                        A clock line that lets a clock pulse sequence the processor
                                                                        A reset line that resets the program counter to zero (or what-
                                                                          ever) and restarts execution
                                                                        Let’s assume that both the address and data buses are 8 bits
To understand how a microprocessor works, it is helpful to look         wide in this example.
inside and learn about the logic used to create one. In the             Here are the components of this simple microprocessor:
process you can also learn about assembly language - the native
                                                                        * Registers A, B and C are simply latches made out of flip-flops.
language of a microprocessor - and many of the things that
                                                                          (See the section on “edge-triggered latches” in How Boolean
engineers can do to boost the speed of a processor.
                                                                          Logic Works for details.)
A microprocessor executes a collection of machine instructions          * The address latch is just like registers A, B and C.
that tell the processor what to do. Based on the instructions, a        * The program counter is a latch with the extra ability to incre-
microprocessor does three basic things:                                   ment by 1 when told to do so, and also to reset to zero when
                                                                          told to do so.
* Using its ALU (Arithmetic/Logic Unit), a microprocessor can
                                                                        * The ALU could be as simple as an 8-bit adder, or it might be
 perform mathematical operations like addition, subtraction,
                                                                          able to add, subtract, multiply and divide 8-bit values. Let’s
  multiplication and division. Modern microprocessors contain
                                                                          assume the latter here.
  complete floating point processors that can perform extremely
                                                                        * The test register is a special latch that can hold values from
  sophisticated operations on large floating point numbers.
                                                                         comparisons performed in the ALU. An ALU can normally
* A microprocessor can move data from one memory location to
                                                                          compare two numbers and determine if they are equal, if one is
                                                                          greater than the other, etc. The test register can also normally
* A microprocessor can make decisions and jump to a new set of
                                                                          hold a carry bit from the last stage of the adder. It stores these
   instructions based on those decisions.
                                                                          values in flip-flops and then the instruction decoder can use
There may be very sophisticated things that a microprocessor              the values to make decisions.
does, but those are its three basic activities. The following           * There are six boxes marked “3-State” in the diagram. These are
diagram shows an extremely simple microprocessor capable of               tri-state buffers. A tri-state buffer can pass a 1, a 0 or it can
doing those three things:                                                 essentially disconnect its output (imagine a switch that totally
                                                                          disconnects the output line from the wire that the output is
                                                                Page 40
  heading toward). A tri-state buffer allows multiple outputs to        ROM stands for read-only memory. A ROM chip is programmed
  connect to a wire, but only one of them to actually drive a 1 or      with a permanent collection of pre-set bytes. The address bus
  a 0 onto the line.                                                    tells the ROM chip which byte to get and place on the data bus.
* The instruction register and instruction decoder are respon           When the RD line changes state, the ROM chip presents the
  sible for controlling all of the other components.                    selected byte onto the data bus.
Although they are not shown in this diagram, there would be
control lines from the instruction decoder that would:
* Tell the A register to latch the value currently on the data bus
* Tell the B register to latch the value currently on the data bus
* Tell the C register to latch the value currently on the data bus
* Tell the program counter register to latch the value currently on
   the data bus
* Tell the address register to latch the value currently on the data
* Tell the instruction register to latch the value currently on the
   data bus
* Tell the program counter to increment                                                            RAM chip
* Tell the program counter to reset to zero                             RAM stands for random-access memory. RAM contains bytes of
* Activate any of the six tri-state buffers (six separate lines)        information, and the microprocessor can read or write to those
* Tell the ALU what operation to perform                                bytes depending on whether the RD or WR line is signaled. One
* Tell the test register to latch the ALU’s test bits                   problem with today’s RAM chips is that they forget everything
* Activate the RD line                                                  once the power goes off. That is why the computer needs ROM.
* Activate the WR line
                                                                        By the way, nearly all computers contain some amount of ROM
Coming into the instruction decoder are the bits from the test          (it is possible to create a simple computer that contains no RAM
register and the clock line, as well as the bits from the instruction   — many microcontrollers do this by placing a handful of RAM
register.                                                               bytes on the processor chip itself — but generally impossible to
                                                                        create one that contains no ROM).
                       RAM and ROM
                                                                        On a PC, the ROM is called the BIOS (Basic Input/Output
The previous section talked about the address and data buses,           System). When the microprocessor starts, it begins executing
as well as the RD and WR lines. These buses and lines connect           instructions it finds in the BIOS. The BIOS instructions do things
either to RAM or ROM - generally both. In our sample micropro-          like test the hardware in the machine, and then it goes to the hard
cessor, we have an address bus 8 bits wide and a data bus 8 bits        disk to fetch the boot sector (see How Hard Disks Work for
wide. That means that the microprocessor can address (28) 256           details). This boot sector is another small program, and the BIOS
bytes of memory, and it can read or write 8 bits of the memory at a     stores it in RAM after reading it off the disk. The microprocessor
time. Let’s assume that this simple microprocessor has 128 bytes        then begins executing the boot sector’s instructions from RAM.
of ROM starting at address 0 and 128 bytes of RAM starting at           The boot sector program will tell the microprocessor to fetch
address 128.                                                            something else from the hard disk into RAM, which the micropro-
                                                                        cessor then executes, and so on. This is how the microprocessor
                                                                        loads and executes the entire operating system.
                                                                                     Microprocessor Performance
                                                                        The number of transistors available has a huge effect on the
                                                                        performance of a processor. As seen earlier, a typical instruction
                                                                        in a processor like an 8088 took 15 clock cycles to execute.
                                                                        Because of the design of the multiplier, it took approximately 80
                                                                        cycles just to do one 16-bit multiplication on the 8088. With more
                                                                        transistors, much more powerful multipliers capable of single-
                                                                        cycle speeds become possible.
                                                                        More transistors also allow for a technology called pipelining. In
                                                                        a pipelined architecture, instruction execution overlaps. So even
                                                                        though it might take five clock cycles to execute each instruction,
                                                                        there can be five instructions in various stages of execution
                                                                        simultaneously. That way it looks like one instruction completes
                            ROM chip                                    every clock cycle.
                                                              Page 41
Many modern processors have multiple instruction decoders,          Servers can definitely benefit from 64 bits, but what about normal
each with its own pipeline. This allows for multiple instruction    users? Beyond the RAM solution, it is not clear that a 64-bit chip
streams, which means that more than one instruction can             offers “normal users” any real, tangible benefits at the moment.
complete during each clock cycle. This technique can be quite       They can process data (very complex data features lots of real
complex to implement, so it takes lots of transistors.              numbers) faster. People doing video editing and people doing
                                                                    photographic editing on very large images benefit from this kind
                 Microprocessor Trends
                                                                    of computing power. High-end games will also benefit, once they
The trend in processor design has primarily been toward full 32-    are re-coded to take advantage of 64-bit features. But the average
bit ALUs with fast floating point processors built in and           user who is reading e-mail, browsing the Web and editing Word
pipelined execution with multiple instruction streams. The newest   documents is not really using the processor in that way. In
thing in processor design is 64-bit ALUs, and people are ex-        addition, operating systems like Windows XP have not yet been
pected to have these processors in their home PCs in the next       upgraded to handle 64-bit CPUs. Because of the lack of tangible
decade.                                                             benefits, it will be 2010 or so before we see 64-bit machines on
                                                                    very desktop.
There has also been a tendency toward special instructions (like
the MMX instructions) that make certain operations particularly
efficient, and the addition of hardware virtual memory support                  Good Boot Guide to Your
and L1 caching on the processor chip. All of these trends push                        Hard Disk
up the transistor count, leading to the multi-million transistor
powerhouses available today. These processors can execute           Nearly every desktop computer and server in use today
about one billion instructions per second!                          contains one or more hard-disk drives. Every mainframe
                                                                    and supercomputer is normally connected to hundreds of
                     64-bit Processors                              them. You can even find VCR-type devices and camcorders
Sixty-four-bit processors have been with us since 1992, and in      that use hard disks instead of tape. These billions of hard
the 21st century they have started to become mainstream. Both       disks do one thing well — they store changing digital
                                                                    information in a relatively permanent form. They give
Intel and AMD have introduced 64-bit chips, and the Mac G5
                                                                    computers the ability to remember things when the power
sports a 64-bit processor. Sixty-four-bit processors have 64-bit    goes out.
ALUs, 64-bit registers, 64-bit buses and so on.
                                                                                         Hard Disk Basics
                                                                    Hard disks were invented in the 1950s. They started as large
                                                                    disks up to 20 inches in diameter holding just a few megabytes.
                                                                    They were originally called “fixed disks” or “Winchesters” (a
                                                                    code name used for a popular IBM product). They later became
                                                                    known as “hard disks” to distinguish them from “floppy disks.”
                                                                    Hard disks have a hard platter that holds the magnetic medium,
                                                                    as opposed to the flexible plastic film found in tapes and floppies.
                                                                    At the simplest level, a hard disk is not that different from a
                                                                    cassette tape. Both hard disks and cassette tapes use the same
                                                                    magnetic recording techniques described in How Tape Recorders
                                                                    Work. Hard disks and cassette tapes also share the major
                                                                    benefits of magnetic storage - the magnetic medium can be easily
One reason why the world needs 64-bit processors is because of      erased and rewritten, and it will “remember” the magnetic flux
their enlarged address spaces. Thirty-two-bit chips are often       patterns stored onto the medium for many years.
constrained to a maximum of 2 GB or 4 GB of RAM access. That
sounds like a lot, given that most home computers currently use     In the next section, I’ll talk about the main differences between
only 256 MB to 512 MB of RAM. However, a 4-GB limit can be a        casette tapes and hard disks.
severe problem for server machines and machines running large                    Cassette Tape vs. Hard Disk
databases. And even home machines will start bumping up
against the 2 GB or 4 GB limit pretty soon if current trends        Let’s look at the big differences between cassette tapes and hard
continue. A 64-bit chip has none of these constraints because a     disks:
64-bit RAM address space is essentially infinite for the foresee-   * The magnetic recording material on a cassette tape is coated
able future — 2^64 bytes of RAM is something on the order of a        onto a thin plastic strip. In a hard disk, the magnetic recording
quadrillion gigabytes of RAM.                                         material is layered onto a high-precision aluminum or glass
                                                                      disk. The hard-disk platter is then polished to mirror-type
With a 64-bit address bus and wide, high-speed data buses on           smoothness.
the motherboard, 64-bit machines also offer faster I/O (input/      * With a tape, you have to fast-forward or reverse to get to any
output) speeds to things like hard disk drives and video cards.       particular point on the tape. This can take several minutes with
These features can greatly increase system performance.
                                                               Page 42
   a long tape. On a hard disk, you can move to any point on the       It is a sealed aluminum box with controller electronics attached to
   surface of the disk almost instantly.                               one side. The electronics control the read/write mechanism and
* In a cassette-tape deck, the read/write head touches the tape        the motor that spins the platters. The electronics also assemble
  directly. In a hard disk, the read/write head “flies” over the       the magnetic domains on the drive into bytes (reading) and turn
  disk, never actually touching it.                                    bytes into magnetic domains (writing). The electronics are all
* The tape in a cassette-tape deck moves over the head at about        contained on a small board that detaches from the rest of the
  2 inches (about 5.08 cm) per second. A hard-disk platter can         drive:
   spin underneath its head at speeds up to 3,000 inches per
  second (about 170 mph or 272 kph)!
* The information on a hard disk is stored in extremely small
   magnetic domains compared to a cassette tape’s. The size of
   these domains is made possible by the precision of the platter
   and the speed of the medium.
Because of these differences, a modern hard disk is able to store
an amazing amount of information in a small space. A hard disk
can also access any of its information in a fraction of a second.
               Capacity and Performance
A typical desktop machine will have a hard disk with a capacity
of between 10 and 40 gigabytes. Data is stored onto the disk in
the form of files. A file is simply a named collection of bytes. The
bytes might be the ASCII codes for the characters of a text file, or
they could be the instructions of a software application for the
computer to execute, or they could be the records of a data base,                     Inside: Beneath the Board
or they could be the pixel colors for a GIF image. No matter what
                                                                       Underneath the board are the connections for the motor that
it contains, however, a file is simply a string of bytes. When a
                                                                       spins the platters, as well as a highly-filtered vent hole that lets
program running on the computer requests a file, the hard disk
                                                                       internal and external air pressures equalize:
retrieves its bytes and sends them to the CPU one at a time.
There are two ways to measure the performance of a hard disk:
Data rate - The data rate is the number of bytes per second
 that the drive can deliver to the CPU. Rates between 5 and 40
 megabytes per second are common.
Seek time - The seek time is the amount of time between when
 the CPU requests a file and when the first byte of the file is
 sent to the CPU. Times between 10 and 20 milliseconds are
The other important parameter is the capacity of the drive, which
is the number of bytes it can hold.
                Inside: Electronics Board
The best way to understand how a hard disk works is to take a
look inside. (Note that opening a Hard Disk Ruins It), so this
is not something to try at home unless you have a defunct drive.)
Here is a typical hard-disk drive:
                                                                       Removing the cover from the drive reveals an extremely simple
                                                                       but very precise interior:
                                                                       In the Figure at the top of Page 44 you can see:
                                                                       * The platters, which typically spin at 3,600 or 7,200 rpm when
                                                                         the drive is operating. These platters are manufactured to
                                                                         amazing tolerances and are mirror-smooth (as you can see in
                                                                         this interesting self-portrait of the author... no easy way to
                                                                         avoid that!).
                                                                       * The arm that holds the read/write heads is controlled by the
                                                                         mechanism in the upper-left corner, and is able to move the
                                                                         heads from the hub to the edge of the drive. The arm and its
                                                                        movement mechanism are extremely light and fast.
                                                              Page 43

The arm on a typical hard-disk drive can move from hub to edge
and back up to 50 times per second - it is an amazing thing to
             Inside: Platters and Heads                                                     Storing the Data
In order to increase the amount of information the drive can          Data is stored on the surface of a platter in sectors and tracks.
store, most hard disks have multiple platters. This drive has three   Tracks are concentric circles, and sectors are pie-shaped wedges
platters and six read/write heads:                                    on a track, like this:

                                                                      A typical track is shown in yellow; a typical sector is shown in
                                                                      blue. A sector contains a fixed number of bytes - for example, 256
                                                                      or 512. Either at the drive or the operating system level, sectors
                                                                      are often grouped together into clusters.
                                                                      The process of low-level formatting a drive establishes the
                                                                      tracks and sectors on the platter. The starting and ending points
                                                                      of each sector are written onto the platter. This process prepares
The mechanism that moves the arms on a hard disk has to be            the drive to hold blocks of bytes. High-level formatting then
incredibly fast and precise. It can be constructed using a high-      writes the file-storage structures, like the file-allocation table, into
speed linear motor.                                                   the sectors. This process prepares the drive to hold files.

Many drives use a “voice coil” approach — the same technique
used to move the cone of a speaker on your stereo is used to
move the arm.
                                                               Page 44
 What’s the churning sound I hear from my
                                                                                   Good Boot Guide to Your
 hard drive whenever it is retrieving data?
Let’s say you do something simple like double-click on the icon
for a spreadsheet file. This simple act, on many computers, can        If the CPU is the brain of the computer, the motherboard and its
take 20 or 30 seconds to complete, and all during that time the        components are the major systems this brain uses to control the
hard disk is churning away. The hard-disk access light flickers        rest of the computer. It is possibly the most important part of the
and the drive might make a whirring, whizzing or high-pitched          computer. Having a good understanding of how the motherboard
whining noise. If the mechanism in the drive is loud, you              and its contained subsystems work is probably the most critical
definitely know that something is going on!                            part of getting a good understanding of how PCs work.
In the article How Hard Disks Work, you can see that there is an
                                                                       Here you can see the connection from the power supply to the
arm that holds the read-write heads. This arm can move the heads
                                                                       motherboard. The power supply serves two functions. First of all
to tracks near the hub or near the edge of the disk. A normal hard
                                                                       it draws power from the outlet (usually 120V AC) and translates it
disk is 5 inches (12.5 cm) or so in diameter. This arm, therefore,
                                                                       into voltages the computer can use (usually 12V DC). It also runs
can move about 2 inches (5 cm) across the face of the disk.
                                                                       the main cooling fan which prevents the computer from overheat-
The speed at which this arm can move is astonishing. The arm is        ing which can be detrimental to the integrity of your data.
very light, and its actuator is powerful and precise. The arm can
slide across the face of the disk hundreds of times per second if it
needs to.
If you think about how a speaker works, there is not much of a
difference. A speaker is moving a lightweight cone back and forth
hundreds of times per second to generate sound. As the hard-
disk arm moves back and forth rapidly, it sets up vibrations that
our ears hear as sounds.
Why, when you click on a simple spreadsheet file, would the
disk’s heads have to move so much (20 or 30 seconds worth of
movement sometimes)? There are three things that cause all the
To start a spreadsheet application like Excel, the hard disk has to
load the application itself along with a number of DLLs (dynamic
link libraries) that support the application. The total size of all             Important is Your Motherboard?
these different files might be 10 to 20 megabytes, and the files are
scattered all over the disk. Loading 20 megabytes of data takes a      The motherboard is the foundation of any PC. All the critical
lot of time and requires the disk head to move thousands of times      subsystems, including the CPU, the system chipset, the memory,
to retrieve all the pieces.                                            the system I/O, the expansion bus, and other critical components
                                                                       run directly off the motherboard. Likewise, the interconnections
The data file itself has to load. The operating system (OS) has to     among these components are built into the motherboard itself. It
move the head to the drive’s directory to find the folder, make        manages all transactions of data between the CPU and the
sure the file name exists, and then discover the location of the       peripherals. It houses the CPU and its second level cache, the
file. Then the OS may need to read dozens of tracks scattered all      chipset, the BIOS, the main memory, the I/O chips, the port for
over the drive to access the file.                                     the keyboard, the serial I/O, the parallel I/O, the disks, and the
If the physical RAM is full, then during the loading process the       plug-in cards.
OS will have to unload parts of physical RAM and save them to
                                                                       Note: The motherboard is also referred to as the mainboard,
the paging file on the disk. So while the OS is trying to load the
                                                                       system board, maincard or mothercard.
spreadsheet application and all the DLLs and the data file, it’s at
the same time trying to write millions of bytes of data to the                            Jack of All Trades
paging file to make room for the new application. The drive head
is moving all over the disk to accomplish these intermingled            The way the motherboard is laid out dictates how the entire
tasks.                                                                 computer is going to be organized. Everything is eventually
                                                                       connected to the motherboard, either directly or indirectly. As
Altogether, clicking on a single icon may cause 40 or 50 mega-         metioned above, it contains the chipset and the BIOS program
bytes of data to move between the drive and RAM, with the disk         which control most of the data flow within the computer. Almost
heads repositioning themselves thousands of times in the               all communication between the PC and its peripherals, other PCs,
process. That is why you hear the drive “churning” - it’s doing a      and you goes through the motherboard.
lot of work!
                                                                       Note: BIOS stand for Basic Input Output System.
                                                                Page 45
The motherboard determines what types of peripherals you can
use in your PC. It also determines what type of processor and
memory you can use. To this end, it directly determines your
system’s performance. The ability to upgrade your machine is
almost entirely dependent on the motherboard.
Note: Intel and Microsoft in 1993 developed Plug and Play?
Note: The motherboard’s general size, layout, and component
placement is know as the form factor.
                                                                         The motherboard is an extremely complex and fascinating
Data exchange within the motherboard is handled by the ROM               component of a computer. It is much more complex than the brief
chip. It contains instructions which are specific for that particular    introduction given here. Please see the links below for more in
motherboard. These instructions will remain in the PC throughout         depth information on the motherboard. As you continue your
its life; usually they are not altered. Primarily the ROM code           travels in search of computer knowledge, remember, the
holds start-up instructions. In fact there are several different         motherboard is to computers what Grand Central Station is to
programs inside the start-up instructions.                               trains.

                                   Cruise the Motherboard

     ISA Slots           PCI Slots                                      Parallel & Serial Slots USB Ports

                                                                                                                      PS/2 Slots
                                                                                                                    For Mouse and

                                                                                                                    Power Supply


                                                                                                                    Memory Sockets

                        Chipset         Battery      Storage Device Connectors
                                                              Page 46
                                                                      IDE was created as a way to standardize the use of hard drives in
           Good Boot Guide to Your                                    computers. The basic concept behind IDE is that the hard drive
                 IDE Device                                           and the controller should be combined. The controller is a small
                                                                      circuit board with chips that provide guidance as to exactly how
No matter what you do with your computer, storage is an               the hard drive stores and accesses data. Most controllers also
important part of your system. In fact, most personal                 include some memory that acts as a buffer to enhance hard drive
computers have one or more of the following storage                   performance.
                                                                      Before IDE, controllers and hard drives were separate and often
* Floppy drive
                                                                      proprietary. In other words, a controller from one manufacturer
* Hard drive
                                                                      might not work with a hard drive from another manufacturer. The
* CD-ROM drive
                                                                      distance between the controller and the hard drive could result in
                                                                      poor signal quality and affect performance. Obviously, this
                                                                      caused much frustration for computer users.
                                                                      IBM introduced the AT computer in 1984 with a couple of key
                                                                      * The slots in the computer for adding cards used a new version
                                                                        of the Industry Standard Architecture (ISA) bus. The new bus
                                                                       was capable of transmitting information 16 bits at a time,
                                                                        compared to 8 bits on the original ISA bus.
                                                                      * IBM also offered a hard drive for the AT that used a new
                                                                       combined drive/controller. A ribbon cable from the drive/
                                                                        controller combination ran to an ISA card to connect to the
                                                                        computer, giving birth to the AT Attachment (ATA) interface.
                                                                      In 1986, Compaq introduced IDE drives in their Deskpro 386. This
                                                                      drive/controller combination was based on the ATA standard
  The hard drive and circuit board combination that
                                                                      developed by IBM. Before long, other vendors began offering
                 typify IDE devices
                                                                      IDE drives. IDE became the term that covered the entire range of
Usually, these devices connect to the computer through an             integrated drive/controller devices. Since almost all IDE drives
Integrated Drive Electronics (IDE) interface. Essentially, an IDE     are ATA-based, the two terms are used interchangeably.
interface is a standard way for a storage device to connect to a
computer. IDE is actually not the true technical name for the                Controllers, Drives, Host Adapters
interface standard. The original name, AT Attachment (ATA),           Most motherboards come with an IDE interface. This interface is
signified that the interface was initially developed for the IBM AT   often referred to as an IDE controller, which is incorrect. The
computer. In this article, you will learn about the evolution of      interface is actually a host adapter, meaning that it provides a
IDE/ATA, what the pinouts are and exactly what “slave” and            way to connect a complete device to the computer (host). The
“master” mean in IDE.                                                 actual controller is on a circuit board attached to the hard drive.
                       IDE Evolution                                  That’s the reason it’s called Integrated Drive Electronics in the
                                                                      first place!
                                                                                                                 A close-up of the
                                                                                                                 primary and sec-
                                                                                                                 ondary IDE inter-
                                                                                                                 faces on a

  The birth of the IDE interface led to combining a
      controller like this one with a hard drive.
                                                              Page 47
While the IDE interface was originally developed for connecting        of ATAPI, ATA-4 immediately improved the removable media
hard drives, it has evolved into the universal interface for           support of ATA. Ultra DMA increased the DMA transfer rate
connecting internal floppy drives, CD-ROM drives and even              from ATA-2’s 16.67 MBps to 33.33 MBps. In addition to the
some tape backup drives. Although it is very popular for internal      existing cable that uses 40 pins and 40 conductors (wires), this
drives, IDE is rarely used for attaching an external device.            version introduces a cable that has 80 conductors. The other
                                                                        40 conductors are ground wires interspersed between the
There are several variations of ATA, each one adding to the
                                                                       standard 40 conductors to improve signal quality. ATA-4 is
previous standard and maintaining backward compatibility.
                                                                       also known as Ultra DMA, Ultra ATA and Ultra ATA/33.
The standards include:                                               * ATA-5 - The major update in ATA-5 is auto detection of which
* ATA-1 - The original specification that Compaq included in           cable is used: the 40-conductor or 80-conductor version. Ultra
   the Deskpro 386. It instituted the use of a master/slave            DMA is increased to 66.67 MB/sec with the use of the 80-
    configuration. ATA-1 was based on a subset of the standard         conductor cable. ATA-5 is also called Ultra ATA/66.
   ISA 96-pin connector that uses either 40 or 44 pin connectors
                                                                                               Cable Key
   and cables. In the 44-pin version, the extra four pins are used
   to supply power to a drive that doesn’t have a separate power     IDE devices use a ribbon cable to connect to each other. Ribbon
  connector. Additionally, ATA-1 provides signal timing for          cables have all of the wires laid flat next to each other instead of
   direct memory access (DMA) and programmed input/output            bunched or wrapped together in a bundle. IDE ribbon cables
  (PIO) functions. DMA means that the drive sends information        have either 40 or 80 wires. There is a connector at each end of the
  directly to memory, while PIO means that the computer’s            cable and another one about two-thirds of the distance from the
  central processing unit (CPU) manages the information              motherboard connector. This cable cannot exceed 18 inches (46
  transfer. ATA-1 is more commonly known as IDE.                     cm) in total length (12 inches from first to second connector, and
* ATA-2 - DMA was fully implemented beginning with the               6 inches from second to third) to maintain signal integrity. The
  ATA-2 version. Standard DMA transfer rates increased from          three connectors are typically different colors and attach to
   4.16 megabytes per second (MBps) in ATA-1 to as many as           specific items:
  16.67 MBps. ATA-2 provides power management, PCMCIA                * The blue connector attaches to the motherboard.
   card support and removable device support. ATA-2 is often         * The black connector attaches to the primary (master) drive.
  called EIDE (Enhanced IDE), Fast ATA or Fast ATA-2. The total      * The grey connector attaches to the secondary (slave) drive.
   hard drive size supported increased to 137.4 gigabytes. ATA-2
   provided standard translation methods for Cylinder Head           Along one side of the cable is a stripe. This stripe tells you that
  Sector (CHS) for hard drives up to 8.4 gigabytes in size. CHS is   the wire on that side is attached to Pin 1 of each connector. Wire
   how the system determines where the data is located on a hard     20 is not connected to anything. In fact, there is no pin at that
   drive. The reason for the big discrepancy between total hard      position. This position is used to ensure that the cable is
   drive size and CHS hard drive support is because of the bit       attached to the drive in the correct position. Another way that
   sizes used by the basic input/output system (BIOS) for CHS.       manufacturers make sure the cable is not reversed is by using a
  CHS has a fixed length for each part of the address. Look at       cable key. The cable key is a small, plastic square on top of the
   this chart:                                                       connector on the ribbon cable that fits into a notch on the
                                                                     connector of the device. This allows the cable to attach in only
                                                                     one position.

You will note that the number of sectors is 63 instead of 64. This
is because a sector cannot begin with zero. Each sector holds 512
bytes. If you multiply 1,024 x 256 x 63 x 512, you will get
8,455,716,864 bytes or approximately 8.4 gigabytes. Newer BIOS
versions increased the bit size for CHS, providing support for the
full 137.4 gigabytes.
* ATA-3 - With the addition of Self-Monitoring Analysis and
  Reporting Technology (SMART), IDE drives were made more
  reliable. ATA-3 also adds password protection to access
  drives, providing a valuable security feature.
* ATA-4 - Probably the two biggest additions to the standard in
  this version are Ultra DMA support and the integration of the
  AT Attachment Program Interface (ATAPI) standard. ATAPI
  provides a common interface for CD-ROM drives, tape backup                       The connector on an IDE cable
  drives and other removable storage devices. Before ATA-4,
  ATAPI was a completely separate standard. With the inclusion
                                                               Page 48
                                                                      either the master jumper removed or a special slave jumper set,
                                                                      depending on the drive. Also, the slave drive is attached to the
                                                                      connector near the middle of the IDE ribbon cable. Each drive’s
                                                                      controller board looks at the jumper setting to determine whether
                                                                      it is a slave or a master. This tells them how to perform. Every
                                                                      drive is capable of being either slave or master when you receive
                                                                      it from the manufacturer. If only one drive is installed, it should
                                                                      always be the master drive.
                                                                      Many drives feature an option called Cable Select (CS). With the
                                                                      correct type of IDE ribbon cable, these drives can be auto
                                                                      configured as master or slave. CS works like this: A jumper on
                                                                      each drive is set to the CS option. The cable itself is just like a
                                                                      normal IDE cable except for one difference - Pin 28 only connects
                                                                      to the master drive connector. When your computer is powered
                                                                      up, the IDE interface sends a signal along the wire for Pin 28.
                                                                      Only the drive attached to the master connector receives the
                                                                      signal. That drive then configures itself as the master drive. Since
                                                                      the other drive received no signal, it defaults to slave mode.

                                                                              Good Boot Guide to Your AGP

Note: the last four pins are only used by devices that require
power through the ribbon cable. Typically, such devices are hard
drives that are too small (for example, 2.5 inches) to need a
separate power supply.
                   Masters and Slaves
A single IDE interface can support two devices. Most
motherboards come with dual IDE interfaces (primary and                                      AGP graphics card
secondary) for up to four IDE devices. Because the controller is
integrated with the drive, there is no overall controller to decide   You point, you click; you drag and you drop. Files open and
which device is currently communicating with the computer. This       close in separate windows. Movies play, pop-ups pop, and video
is not a problem as long as each device is on a separate interface,   games fill the screen, immersing you in a world of 3-D graphics.
but adding support for a second drive on the same cable took          This is the stuff we’re used to seeing on our computers.
some ingenuity.                                                       It all started in 1973, when Xerox completed the Alto, the first
To allow for two drives on the same cable, IDE uses a special         computer to use a graphical user interface. This innovation
configuration called master and slave. This configuration allows      forever changed the way the people work with their computers.
one drive’s controller to tell the other drive when it can transfer   Today, every aspect of computing, from creating animation to
data to or from the computer. What happens is the slave drive         simple tasks such as word processing and e-mail, uses lots of
makes a request to the master drive, which checks to see if it is     graphics to create a more intuitive work environment for the user.
currently communicating with the computer. If the master drive is     The hardware to support these graphics is called a graphics card.
idle, it tells the slave drive to go ahead. If the master drive is    The way this card connects to your computer is key in your
communicating with the computer, it tells the slave drive to wait     computer’s ability to render graphics. In this article, you will learn
and then informs it when it can go ahead.                             about AGP, or Accelerated Graphics Port. AGP enables your
The computer determines if there is a second (slave) drive            computer to have a dedicated way to communicate with the
attached through the use of Pin 39 on the connector. Pin 39           graphics card, enhancing both the look and speed of your
carries a special signal, called Drive Active/Slave Present           computer’s graphics.
(DASP), that checks to see if a slave drive is present.                                 A bit about the BUS
Although it will work in either position, it is recommended that      In 1996, Intel introduced AGP as a more efficient way to deliver
the master drive is attached to the connector at the very end of      the streaming video and real-time-rendered 3-D graphics that
the IDE ribbon cable. Then, a jumper on the back of the drive next    were becoming more prevalent in all aspects of computing.
to the IDE connector must be set in the correct position to           Previously, the standard method of delivery was the Peripheral
identify the drive as the master drive. The slave drive must have
                                                            Page 49
Component Interconnect (PCI) bus. The PCI bus is a path used                         Out With the Old...
to deliver information from the graphics card to the central
processing unit (CPU). A bus allows multiple packets of informa-   AGP is built on the idea of improving the ways that PCI trans-
tion from different sources to travel down one path simulta-       ports data to the CPU. Intel achieved this by addressing all of the
neously. Information from the graphics card travels through the    areas where PCI transfers were causing data bottlenecks in the
bus along with any other information that is coming from a         system. By clearing the traffic jams of data, AGP increases the
device connected to the PCI. When all the information arrives at   speed at which machines can render graphics while using the
the CPU, it has to wait in line to get time with the CPU.          system’s resources more efficiently to reduce overall drag. Here’s
                                                                   * Dedicated Port - There are no other devices connected to the
                                                                     AGP other than the graphics card. With a dedicated path to the
                                                                     CPU, the graphics card can always operate at the maximum
                                                                      capacity of the connection.
                                                                   * Pipelining - This method of data organization allows the
                                                                     graphics card to receive and respond to multiple packets of
                                                                     data in a single request. Here’s a simplified example of this:
                                                                      With AGP, the graphics card can receive a request for all of
                                                                      the information needed to render a particular image and send
                                                                      it out all at once. With PCI, the graphics card would receive
                                                                      information on the height of the image and wait... then the
                                                                      length of the image, and wait... then the width of the image,
                                                                       and wait... combine the data, and then send it out.
                                                                   * Sideband addressing - Like a letter, all requests and informa-
                                                                     tion sent from one part of your computer to the next must have
                                                                     an address containing “To” and “From.” The problem with PCI
                                                                     is that this “To” and “From” information is sent with the
                PCI slots on a motherboard                           working data all together in one packet. This is the equivalent
This system worked well for many years, but eventually the PCI       of including an address card inside the envelope when you
bus became a little long in the tooth. The Internet and most         send a letter to a friend: Now the post office has to open the
software were more and more graphically oriented, and the            envelope to see the address in order to know where to send it.
demands of the graphics card needed priority over all other PCI      This takes up the post office’s time. In addition, the address
devices.                                                             card itself takes up room in the envelope, reducing the total
                                                                     amount of stuff you can send to your friend.
                                                                     With sideband addressing, the AGP issues eight additional
                                                                     lines on the data packet just for addressing. This puts the
                                                                     address on the outside of the envelope, so to speak, freeing up
                                                                     the total bandwidth of the data path used to transfer informa-
                                                                     tion back and forth. In addition, it unclogs system resources
                                                                     that were previously used to open the packet to read the
                                                                                      PCI: Wasting RAM
                                                                   Speed is not the only area where AGP has bested its predecessor.
                                                                   It also streamlines the process of rendering graphics by using
                                                                   system memory more efficiently.
                                                                   Any 3-D graphic you see on your computer is built by a texture
                                                                   map. Texture maps are like wrapping paper. Your computer takes a
                                                                   flat, 2-D image and wraps it around a set of parameters dictated
   Typical example of an AGP-based graphics card                   by the graphics card to create the appearance of a 3-D image.
AGP is based on the design of the PCI bus; but unlike a bus, it    Think of this as wrapping an invisible box with wrapping paper to
provides a dedicated point-to-point connection from the graphics   show the size of the box. It is important to understand this
card to the CPU. With a clear path to the CPU and system           because the creation and storage of texture maps is the main
memory, AGP provides a much faster, more efficient way for your    thing that drains the memory from both the graphics card and the
computer to get the information it needs to render complex         system overall.
graphics. In the next section, we’ll see how this is done.
                                                                  Page 50
With a PCI-based graphics card, every texture map has to be
stored twice. First, the texture map is loaded from the hard drive
to the system memory (RAM) until it has to be used. Once it is
needed, it is pulled from memory and sent to the CPU to be
processed. Once processed, it is sent through the PCI bus to the
graphics card, where it is stored again in the card’s framebuffer.
The framebuffer is where the graphics card holds the image in
storage once it has been rendered so that it can be refreshed
every time it is needed. All of this storing and sending between
the system and the card is very draining to the overall perfor-
mance of the computer.

                                                                          Diagram of the standard architecture of a Pentium
                                                                          III-based system using AGP
                                                                                                 AGP Today
                                                                          AGP and AGP graphics cards are now the standard for
                                                                          processing graphics on computers. Like all hardware, the
With PCI, texture maps are loaded from the hard drive
                                                                          technology and specifications are constantly improving.
to system memory, processed by the CPU and then loaded
into the framebuffer of the graphics card.                                          Good Boot Guide to Your
                     AGP: Saving RAM                                                      Sound Card
AGP improves the process of storing texture maps by allowing
the operating system to designate RAM for use by the graphics
card on the fly. This type of memory is called AGP memory or
non-local video memory. Using the much more abundant and
faster RAM used by the operating system to store texture maps
reduces the number of maps that have to be stored on the
graphics card’s memory. In addition, the size of the texture map
your computer is capable of processing is no longer limited to the
amount of RAM on the graphics card.

The other way AGP saves RAM is by only storing texture maps               Industry Standard Architecture 16-bit sound card
once. It does this with a little trickery. This trickery takes the form   The voice in your computer that lets you know when you’ve
of a chipset called the Graphics Address Remapping Table                  received a new e-mail is made possible by the sound card.
(GART). GART takes the portion of the system memory that the              Before the arrival of sound cards, personal computers (PCs)
AGP borrows to store texture maps for the graphics card and re-           were limited to beeps from a tiny speaker on the motherboard.
addresses it. The new address provided by GART makes the CPU              In the late 1980s, sound cards ushered in the multimedia PC
think that the texture map is being stored in the card’s                  and took computer games to a whole different level.
framebuffer. GART may be putting bits and pieces of the map all
over the system RAM; but when the CPU needs it, as far as it’s            In 1989, Creative Labs introduced the Creative Labs
concerned the texture map is right where it should be.                    SoundBlaster® card. Since then, many other companies have
                                                                          introduced sound cards, and Creative has continued to
                                                                          improve the SoundBlaster line.
                                                            Page 51
In this chapter you’ll learn how a sound card works and explore     * a digital input source
the many uses for this technology. You will also learn what FM        * digital audiotape (DAT)
and wavetable synthesis mean.                                        * CD-ROM drive
                                                                    * an analog output device - tape deck
              Anatomy of a Sound Card                               * a digital output device
A typical sound card has:                                             * DAT
* a digital signal processor (DSP) that handles most computa-        * CD recordable (CD-R)
  tions                                                             Some of the current high-end sound cards offer four-speaker
* a digital to analog converter (DAC) for audio leaving the         output and digital interface through a jack. For audiophiles, there
  computer                                                          is a new generation of digital sound cards. A digital sound card is
* an analog-to-digital converter (ADC) for audio coming into the    practical for applications that need digital sound, such as CD-R
  computer                                                          and DAT. Staying digital without any conversion to or from
* read-only memory (ROM) or Flash memory for storing data           analog helps prevent what is called “generational loss.” Digital
* musical instrument digital interface (MIDI) for connecting to     sound cards have provisions for digital sound input and output,
  external music equipment (for many cards, the game port is also   so you can transfer data from DAT, DVD or CD directly to your
  used to connect an external MIDI adapter)                         hard disk in your PC.
* jacks for connecting speakers and microphones, as well as line
  in and line out                                                                      Catching The Wave
* a game port for connecting a joystick or gamepad                  Typically, a sound card can do four things with sound:
Current sound cards usually plug into a Peripheral Component        * play pre-recorded music (from CDs or sound files, such as wav
Interconnect (PCI) slot, while some older or inexpensive cards       or MP3), games or DVDs
may use the Industry Standard Architecture (ISA) bus. Many of       * record audio in various media from external sources (micro
the computers available today incorporate the sound card as a         phone or tape player)
chipset right on the motherboard. This leaves another slot open     * synthesize sounds
for other peripherals. The SoundBlaster Pro is considered the de    * process existing sounds
facto standard for sound cards. Virtually every sound card on the
                                                                    The DAC and ADC provide the means for getting the audio in
market today includes SoundBlaster Pro compatibility as a bare
                                                                    and out of the sound card while the DSP oversees the process.
                                                                    The DSP also takes care of any alterations to the sound, such as
                                                                    echo or reverb. Because the DSP focuses on the audio process-
                                                                    ing, the computer’s main processor can take care of other tasks.
                                                                    Early sound cards used FM synthesis to create sounds. FM
                                                                    synthesis takes tones at varying frequencies and combines them
                                                                    to create an approximation of a particular sound, such as the
                                                                    blare of a trumpet. While FM synthesis has matured to the point
                                                                    where it can sound very realistic, it does not compare to
                                                                    wavetable synthesis. Wavetable synthesis works by recording a
                                                                    tiny sample of the actual instrument. This sample is then played
                                                                    in a loop to re-create the original instrument with incredible
                                                                    accuracy. Wavetable synthesis has become the standard for most
                                                                    sound cards, but some of the inexpensive brands still use FM
                                                                    synthesis. A few cards provide both types.
      Creative Labs SB4740 Sound Blaster 16 PCI
                                                                    Very sophisticated sound cards have more support for MIDI
Often, different brands of sound cards from different manufactur-   instruments. Using a music program, a MIDI-equipped music
ers use the same chipset. The basic chipset comes from a third-     instrument can be attached to the sound card to allow you to see
party vendor. The sound card manufacturer then adds various         on the computer screen the music score of what you’re playing.
other functions and bundled software to help differentiate their
                                                                                          Producing Sound
Sound cards may be connected to:                                    Let’s say you speak into your computer’s microphone. A sound
                                                                    card creates a sound file in wav format from the data input
* headphones
                                                                    through the microphone. The process of converting that data
* amplified speakers
                                                                    into a file to be recorded to the hard disk is:
* an analog input source
  * microphone                                                      1. The sound card receives a continuous, analog-waveform input
  * radio                                                             signal from the microphone jack. The analog signals received
  * tape deck                                                          vary in both amplitude and frequency.
  * CD player
                                                              Page 52

                                                                                  Good Boot Guide to Your
2. Software in the computer selects which input(s) will be used,
   depending on whether the microphone sound is being mixed
  with a CD in the CD-ROM drive.                                                       Parallel Ports
3. The mixed, analog waveform signal is processed in real-time by
  an analog-to-digital converter (ADC) circuit chip, creating a       If you have a printer connected to your computer, there is a good
   binary (digital) output of 1s and 0s.                              chance that it uses the parallel port. While USB is becoming
4. The digital output from the ADC flows into the DSP. The DSP        increasingly popular, the parallel port is still a commonly used
   is programmed by a set of instructions stored on another chip      interface for printers.
   on the sound card. One of the functions of the DSP is to
   compress the now-digital data in order to save space. The DSP
   also allows the computer’s processor to perform other tasks
   while this is taking place.
5. The output from the DSP is fed to the computer’s data bus by
   way of connections on the sound card (or traces on the
   motherboard to and from the sound chipset).
6. The digital data is processed by the computer’s processor and
   routed to the hard-disk controller. It is then sent on to the
   hard-disk drive as a recorded wav file.
To listen to a prerecorded wav file, the process is simply re-        A typical parallel port on the back of your computer
versed:                                                               Parallel ports can be used to connect a host of popular computer
1. The digital data is read from the hard disk and passed on to the   peripherals:
   central processor.                                                 * Printers
2. The central processor passes the data to the DSP on the sound      * Scanners
   card.                                                              * CD burners
3. The DSP uncompresses the digital data.                             * External hard drives
4. The uncompressed, digital data-stream from the DSP is              * Iomega Zip removable drives
  processed in real-time by a digital-to-analog converter (DAC)       * Network adapters
   circuit chip, creating an analog signal that you hear in the       * Tape backup drives
   headphones or through the speakers, depending on which is
   connected to the sound-card’s headphone jack.                      In this chapter, you will learn why it is called the parallel port,
                                                                      what it does and exactly how it operates.
                 Sound Card Upgrades
                                                                                          Parallel Port Basics
Sound-card upgrades are an option if the motherboard does not
have a sound chipset built in or if the user wants higher perfor-     Parallel ports were originally developed by IBM as a way to
mance. A common upgrade path is to move from an ISA sound             connect a printer to your PC. When IBM was in the process of
card to a PCI sound card. Generally, your intended application        designing the PC, the company wanted the computer to work
determines whether you need a new sound card. For some audio          with printers offered by Centronics, a top printer manufacturer at
applications, such as telephony or certain games, full-duplex         the time. IBM decided not to use the same port interface on the
sound is a must. Full-duplex sound has the ability to accept a        computer that Centronics used on the printer.
sound input while simultaneously providing sound output.              Instead, IBM engineers coupled a 25-pin connector, DB-25, with
In Windows, you can test for full-duplex capability by launching      a 36-pin Centronics connector to create a special cable to
two copies of Sound Recorder. To do this, click:                      connect the printer to the computer. Other printer manufacturers
                                                                      ended up adopting the Centronics interface, making this strange
1. Start menu
                                                                      hybrid cable an unlikely de facto standard.
2. Programs
3. Accessories                                                        When a PC sends data to a printer or other device using a parallel
4. Entertainment                                                      port, it sends 8 bits of data (1 byte) at a time. These 8 bits are
5. Sound recorder                                                     transmitted parallel to each other, as opposed to the same eight
                                                                      bits being transmitted serially (all in a single row) through a serial
Repeat the process to launch two copies of the program. You can
                                                                      port. The standard parallel port is capable of sending 50 to 100
test for full duplex by playing a file on one Windows Sound
                                                                      kilobytes of data per second.
Recorder and, while that file is playing, making a recording with
the other.                                                            Let’s take a closer look at what each pin does when used with a
                                                                      * Pin 1 carries the strobe signal. It maintains a level of between
                                                                        2.8 and 5 volts, but drops below 0.5 volts whenever the
                                                                        computer sends a byte of data. This drop in voltage tells the
                                                                        printer that data is being sent.
                                                                   Page 53
* Pins 2 through 9 are used to carry data. To indicate that a bit
  has a value of 1, a charge of 5 volts is sent through the correct
  pin. No charge on a pin indicates a value of 0. This is a simple
  but highly effective way to transmit digital information over an
 analog cable in real-time.
* Pin 10 sends the acknowledge signal from the printer to the
  computer. Like Pin 1, it maintains a charge and drops the
  voltage below 0.5 volts to let the computer know that the data
  was received.
* If the printer is busy, it will charge Pin 11. Then, it will drop the
  voltage below 0.5 volts to let the computer know it is ready to
  receive more data.
* The printer lets the computer know if it is out of paper by
  sending a charge on Pin 12.
* As long as the computer is receiving a charge on Pin 13, it
  knows that the device is online.

* The computer sends an auto feed signal to the printer
  through Pin 14 using a 5-volt charge.
* If the printer has any problems, it drops the voltage to less
  than 0.5 volts on Pin 15 to let the computer know that there is
  an error.
* Whenever a new print job is ready, the computer drops the
  charge on Pin 16 to initialize the printer.
* Pin 17 is used by the computer to remotely take the printer
  offline. This is accomplished by sending a charge to the
  printer and maintaining it as long as you want the printer
* Pins 18-25 are grounds and are used as a reference signal for
 the low (below 0.5 volts) charge. (See Figure Column 2).
                         SPP/EPP/ECP                                      Notice how the first 25 pins on the Centronics end match
                                                                          up with the pins of the first connector. With each byte
                                                                          the parallel port sends out, a handshaking signal is also
                                                                          sent so that the printer can latch the byte.

                                                                          information can only travel in one direction at a time. But pins 18
                                                                          through 25, originally just used as grounds, can be used as data
                                                                          pins also. This allows for full-duplex (both directions at the same
                                                                          time) communication.
                                                                          Enhanced Parallel Port (EPP) was created by Intel, Xircom and
                                                                          Zenith in 1991. EPP allows for much more data, 500 kilobytes to 2
                                                                          megabytes, to be transferred each second. It was targeted
                                                                          specifically for non-printer devices that would attach to the
The original specification for parallel ports was unidirectional,         parallel port, particularly storage devices that needed the highest
meaning that data only traveled in one direction for each pin.            possible transfer rate.
With the introduction of the PS/2 in 1987, IBM offered a new
bidirectional parallel port design. This mode is commonly known
as Standard Parallel Port (SPP) and has completely replaced the
original design. Bidirectional communication allows each device
to receive data as well as transmit it. Many devices use the eight
pins (2 through 9) originally designated for data. Using the same
eight pins limits communication to half-duplex, meaning that
                                                                  Page 54
Close on the heels of the introduction of EPP, Microsoft and          ports. USB ports are only a few years old, and will likely replace
Hewlett Packard jointly announced a specification called              both serial and parallel ports completely over the next several
Extended Capabilities Port (ECP) in 1992. While EPP was geared        years.
toward other devices, ECP was designed to provide improved
                                                                      The name “serial” comes from the fact that a serial port “serial-
speed and functionality for printers.
                                                                      izes” data. That is, it takes a byte of data and transmits the 8 bits
                                                                      in the byte one at a time. The advantage is that a serial port
                                                                      needs only one wire to transmit the 8 bits (while a parallel port
                                                                      needs 8). The disadvantage is that it takes 8 times longer to
                                                                      transmit the data than it would if there were 8 wires. Serial ports
                                                                      lower cable costs and make cables smaller.
                                                                      Before each byte of data, a serial port sends a start bit, which is a
                                                                      single bit with a value of 0. After each byte of data, it sends a
                                                                      stop bit to signal that the byte is complete. It may also send a
                                                                      parity bit.
                                                                      Serial ports, also called communication (COM) ports, are bi-
                                                                      directional. Bi-directional communication allows each device to
In 1994, the IEEE 1284 standard was released. It included the two     receive data as well as transmit it. Serial devices use different
specifications for parallel port devices, EPP and ECP. In order for   pins to receive and transmit data - using the same pins would
them to work, both the operating system and the device must           limit communication to half-duplex, meaning that information
support the required specification. This is seldom a problem          could only travel in one direction at a time. Using different pins
today since most computers support SPP, ECP and EPP and will          allows for full-duplex communication, in which information can
detect which mode needs to be used, depending on the attached         travel in both directions at once.
device. If you need to manually select a mode, you can do so
through the BIOS on most computers.

Good Boot Guide to Your Serial Ports
Considered to be one of the most basic external connections to a
computer, the serial port has been an integral part of most
computers for more than 20 years. Although many of the newer
systems have done away with the serial port completely in favor
of USB connections, most modems still use the serial port, as do
some printers, PDAs and digital cameras. Few computers have           This 40-pin Dual Inline Package (DIP) chip is a variation of
more than two serial ports.                                           the National Semiconductor NS16550D UART chip.
                                                                      Serial ports rely on a special controller chip, the Universal
                                                                      Asynchronous Receiver/Transmitter (UART), to function
                                                                      properly. The UART chip takes the parallel output of the
                                                                      computer’s system bus and transforms it into serial form for
                                                                      transmission through the serial port. In order to function faster,
                                                                      most UART chips have a built-in buffer of anywhere from 16 to
                                                                      64 kilobytes. This buffer allows the chip to cache data coming in
                                                                      from the system bus while it is processing data going out to the
                                                                      serial port. While most standard serial ports have a maximum
                                                                      transfer rate of 115 Kbps (kilobits per second), high speed serial
             Two serial ports on the back of a PC
                                                                      ports, such as Enhanced Serial Port (ESP) and Super Enhanced
Essentially, serial ports provide a standard connector and            Serial Port (Super ESP), can reach data transfer rates of 460 Kbps.
protocol to let you attach devices, such as modems, to your
computer. In this edition of How Stuff Works, you will learn
                                                                                        The Serial Connection
about the difference between a parallel port and a serial port,       The external connector for a serial port can be either 9 pins or 25
what each pin does and what flow control is.                          pins. Originally, the primary use of a serial port was to connect a
                       UART Needed
                                                                      modem to your computer. The pin assignments reflect that. Let’s
                                                                      take a closer look at what happens at each pin when a modem is
All computer operating systems in use today support serial            connected.
ports, because serial ports have been around for decades. Parallel
ports are a more recent invention and are much faster than serial
                                                         Page 55
                                                                8. Received Line Signal Detector - Determines if the modem is
                                                                   connected to a working phone line.
                                                                9. Not Used: Transmit Current Loop Return (+)
                                                                10. Not Used
                                                                11. Not Used: Transmit Current Loop Data (-)
                                                                12. Not Used
                                                                13. Not Used
                                                                14. Not Used
                                                                15. Not Used
                                                                16. Not Used
                                                                17. Not Used
                                                                17. Not Used: Receive Current Loop Data (+)
                                                                19. Not Used
                                                                20. Data Terminal Ready - Computer tells the modem that it is
                                                                    ready to talk.
                                                                21. Not Used
                                                                22. Ring Indicator - Once a call has been placed, computer
                                                                    acknowledges signal (sent from modem) that a ring is
                                                                23. Not Used
                                                                24. Not Used
                                                                25. Not Used: Receive Current Loop Return (-)
                                                                Voltage sent over the pins can be in one of two states, On or Off.
                                                                On (binary value “1”) means that the pin is transmitting a signal
                                                                between -3 and -25 volts, while Off (binary value “0”) means that
       Close-up of 9-pin and 25-pin serial connectors           it is transmitting a signal between +3 and +25 volts...

9-pin connector:                                                                  Going With The Flow
1. Carrier Detect - Determines if the modem is connected to a   An important aspect of serial communications is the concept of
  working phone line.                                           flow control. This is the ability of one device to tell another
2. Receive Data - Computer receives information sent from the   device to stop sending data for a while. The commands Request
  modem.                                                        to Send (RTS), Clear To Send (CTS), Data Terminal Ready (DTR)
3. Transmit Data - Computer sends information to the modem.     and Data Set Ready (DSR) are used to enable flow control.
4. Data Terminal Ready - Computer tells the modem that it is
   ready to talk.
5. Signal Ground - Pin is grounded.
6. Data Set Ready - Modem tells the computer that it is ready
  to talk.
7. Request To Send - Computer asks the modem if it can send
8. Clear To Send - Modem tells the computer that it can send
9. Ring Indicator - Once a call has been placed, computer
  acknowledges signal (sent from modem) that a ring is
25-pin connector:
1. Not Used
2. Transmit Data - Computer sends information to the modem.
3. Receive Data - Computer receives information sent from the                       A dual serial port card
   modem.                                                       Let’s look at an example of how flow control works: You have a
4. Request To Send - Computer asks the modem if it can send     modem that communicates at 56 Kbps. The serial connection
   information.                                                 between your computer and your modem transmits at 115 Kbps,
5. Clear To Send - Modem tells the computer that it can send    which is over twice as fast. This means that the modem is getting
   information.                                                 more data coming from the computer than it can transmit over the
6. Data Set Ready - Modem tells the computer that it is ready   phone line. Even if the modem has a 128K buffer to store data in,
    to talk.                                                    it will still quickly run out of buffer space and be unable to
7. Signal Ground - Pin is grounded.                             function properly with all that data streaming in.
                                                               Page 56
With flow control, the modem can stop the flow of data from the        Your Internet connection is the slowest link in your computer. So
computer before it overruns the modem’s buffer. The computer is        your browser (Internet Explorer, Netscape, Opera, etc.) uses the
constantly sending a signal on the Request to Send pin, and            hard disk to store HTML pages, putting them into a special folder
checking for a signal on the Clear to Send pin. If there is no Clear   on your disk. The first time you ask for an HTML page, your
to Send response, the computer stops sending data, waiting for         browser renders it and a copy of it is also stored on your disk.
the Clear to Send before it resumes. This allows the modem to          The next time you request access to this page, your browser
keep the flow of data running smoothly.                                checks if the date of the file on the Internet is newer than the one
                                                                       cached. If the date is the same, your browser uses the one on
            Good Boot Guide to Your                                    your hard disk instead of downloading it from Internet. In this

               Computer Memory
                                                                       case, the smaller but faster memory system is your hard disk and
                                                                       the larger and slower one is the Internet.
                                                                       Cache can also be built directly on peripherals. Modern hard
When you think about it, it’s amazing how many different types         disks come with fast memory, around 512 kilobytes, hardwired to
of electronic memory you encounter in daily life. Many of them         the hard disk. The computer doesn’t directly use this memory —
have become an integral part of our vocabulary:                        the hard-disk controller does. For the computer, these memory
RAM: Random access memory is the best known form of                    chips are the disk itself. When the computer asks for data from
computer memory. RAM is considered “random access” because             the hard disk, the hard-disk controller checks into this memory
you can access any memory cell directly if you know the row and        before moving the mechanical parts of the hard disk (which is
column that intersect at that cell. The opposite of RAM is serial      very slow compared to memory). If it finds the data that the
access memory (SAM). SAM stores data as a series of memory             computer asked for in the cache, it will return the data stored in
cells that can only be accessed sequentially (like a cassette tape).   the cache without actually accessing data on the disk itself,
If the data is not in the current location, each memory cell is        saving a lot of time.
checked until the needed data is found. SAM works very well for        Here’s an experiment you can try. Your computer caches your
memory buffers, where the data is normally stored in the order in      floppy drive with main memory, and you can actually see it
which it will be used (a good example is the texture buffer memory     happening. Access a large file from your floppy — for example,
on a video card). RAM data, on the other hand, can be accessed         open a 300-kilobyte text file in a text editor. The first time, you will
in any order.                                                          see the light on your floppy turning on, and you will wait. The
ROM: Read-only memory also known as firmware, is an                    floppy disk is extremely slow, so it will take 20 seconds to load
integrated circuit programmed with specific data when it is            the file. Now, close the editor and open the same file again. The
manufactured. ROM chips are used not only in computers, but in         second time (don’t wait 30 minutes or do a lot of disk access
most other electronic items as well.                                   between the two tries) you won’t see the light turning on, and
                                                                       you won’t wait. The operating system checked into its memory
Computer Caches: A computer is a machine in which we                   cache for the floppy disk and found what it was looking for. So
measure time in very small increments. When the microprocessor         instead of waiting 20 seconds, the data was found in a memory
accesses the main memory (RAM), it does it in about 60 nanosec-        subsystem much faster than when you first tried it (one access to
onds (60 billionths of a second). That’s pretty fast, but it is much   the floppy disk takes 120 milliseconds, while one access to the
slower than the typical microprocessor. Microprocessors can            main memory takes around 60 nanoseconds — that’s a lot faster).
have cycle times as short as 2 nanoseconds, so to a microproces-       You could have run the same test on your hard disk, but it’s more
sor 60 nanoseconds seems like an eternity.                             evident on the floppy drive because it’s so slow.
What if we build a special memory bank, small but very fast            Dynamic RAM: DRAM Dynamic random access memory has
(around 30 nanoseconds)? That’s already two times faster than          memory cells with a paired transistor and capacitor requiring
the main memory access. That’s called a level 2 cache or an L2         constant refreshing. FPM DRAM Fast page mode dynamic
cache. What if we build an even smaller but faster memory              random access memory was the original form of DRAM. It
system directly into the microprocessor’s chip? That way, this         waits through the entire process of locating a bit of data by
memory will be accessed at the speed of the microprocessor and         column and row and then reading the bit before it starts on the
not the speed of the memory bus. That’s an L1 cache, which on a        next bit. Maximum transfer rate to L2 cache is approximately 176
233-megahertz (MHz) Pentium is 3.5 times faster than the L2            MBps. EDO DRAM Extended data-out dynamic random
cache, which is two times faster than the access to main memory.       access memory does not wait for all of the processing of the
There are a lot of subsystems in a computer; you can put cache         first bit before continuing to the next one. As soon as the
between many of them to improve performance. Here’s an                 address of the first bit is located, EDO DRAM begins looking for
example. We have the microprocessor (the fastest thing in the          the next bit. It is about five percent faster than FPM. Maximum
computer). Then there’s the L1 cache that caches the L2 cache          transfer rate to L2 cache is approximately 264 MBps. SDRAM
that caches the main memory which can be used (and is often            Synchronous dynamic random access memory takes advan-
used) as a cache for even slower peripherals like hard disks and       tage of the burst mode concept to greatly improve performance.
CD-ROMs. The hard disks are also used to cache an even slower          It does this by staying on the row containing the requested bit
medium — your Internet connection.                                     and moving rapidly through the columns, reading each bit as it
                                                                Page 57
The idea is that most of the time the data needed by the CPU will
be in sequence. SDRAM is about five percent faster than EDO
RAM and is the most common form in desktops today. Maximum
transfer rate to L2 cache is approximately 528 MBps. DDR
SDRAM Double data rate synchronous dynamic RAM is just
like SDRAM except that is has higher bandwidth, meaning
greater speed. Maximum transfer rate to L2 cache is approxi-
mately 1,064 MBps (for DDR SDRAM 133 MHZ). RDRAM
Rambus dynamic random access memory is a radical departure
from the previous DRAM architecture. Designed by Rambus,
RDRAM uses a Rambus in-line memory module (RIMM),
which is similar in size and pin configuration to a standard
DIMM. What makes RDRAM so different is its use of a special
high-speed data bus called the Rambus channel. RDRAM
memory chips work in parallel to achieve a data rate of 800 MHz,
or 1,600 MBps.
Static RAM: SRAM Static random access memory uses
multiple transistors, typically four to six, for each memory cell but
doesn’t have a capacitor in each cell. It is used primarily for
                                                                        As you can see in the diagram above, the CPU accesses memory
                                                                        according to a distinct hierarchy. Whether it comes from perma-
Flash memory: Electronic memory comes in a variety of forms to          nent storage (the hard drive) or input (the keyboard), most data
serve a variety of purposes. Flash memory is used for easy and          goes in random access memory (RAM) first. The CPU then stores
fast information storage in such devices as digital cameras and         pieces of data it will need to access, often in a cache, and
home video game consoles. It is used more as a hard drive than          maintains certain special instructions in the register. We’ll talk
as RAM. In fact, Flash memory is considered a solid state               about cache and registers later.
storage device. Solid state means that there are no moving parts
                                                                        All of the components in your computer, such as the CPU, the
— everything is electronic instead of mechanical. Here are a few
                                                                        hard drive and the operating system, work together as a team,
examples of Flash memory: Your computer’s BIOS chip,
                                                                        and memory is one of the most essential parts of this team. From
CompactFlash (most often found in digital cameras),
                                                                        the moment you turn your computer on until the time you shut it
SmartMedia (most often found in digital cameras), Memory Stick
                                                                        down, your CPU is constantly using memory. Let’s take a look at
(most often found in digital cameras), PCMCIA Type I and Type
                                                                        a typical scenario:
II memory cards (used as solid-state disks in laptops) and
Memory cards for video game consoles                                    * You turn the computer on.
                                                                        * The computer loads data from read-only memory (ROM) and
Virtual memory: Virtual memory is a common part of most                   performs a power-on self-test (POST) to make sure all the
operating systems on desktop computers. It has become so                  major components are functioning properly. As part of this test,
common because it provides a big benefit for users at a very low          the memory controller checks all of the memory addresses
cost.                                                                     with a quick read/write operation to ensure that there are no
BIOS: You already know that the computer in front of you has              errors in the memory chips. Read/write means that data is
memory. What you may not know is that most of the electronic              written to a bit and then read from that bit.
items you use every day have some form of memory also. Here             * The computer loads the basic input/output system (BIOS)
are just a few examples of the many items that use memory: Cell           from ROM. The BIOS provides the most basic information
phones. PDAs, Game consoles, Car radios, VCRs and TVs. Each                about storage devices, boot sequence, security, Plug and Play
of these devices uses different types of memory in different              (autodevice recognition) capability and a few other items.
ways!                                                                   * The computer loads the operating system (OS) from the
                                                                          hard drive into the system’s RAM. Generally, the critical parts
In this article, you’ll learn why there are so many different types       of the operating system are maintained in RAM as long as the
of memory and what all of the terms mean.                                 computer is on. This allows the CPU to have immediate access
                       Memory Basics                                       to the operating system, which enhances the performance and
                                                                          functionality of the overall system.
Although memory is technically any form of electronic storage, it       * When you open an application, it is loaded into RAM. To
is used most often to identify fast, temporary forms of storage. If        conserve RAM usage, many applications load only the essen
your computer’s CPU had to constantly access the hard drive to            tial parts of the program initially and then load other pieces as
retrieve every piece of data it needs, it would operate very slowly.       needed.
When the information is kept in memory, the CPU can access it           * After an application is loaded, any files that are opened for use
much more quickly. Most forms of memory are intended to store             in that application are loaded into RAM.
data temporarily.
                                                                 Page 58
* When you save a file and close the application, the file is        can process 2 bytes at a time (1 byte = 8 bits, so 16 bits = 2
  written to the specified storage device, and then it and the       bytes), and a 64-bit CPU can process 8 bytes at a time.
 application are purged from RAM.
                                                                     Megahertz (MHz) is a measure of a CPU’s processing speed, or
In the list above, every time something is loaded or opened, it is   clock cycle, in millions per second. So, a 32-bit 800-MHz Pentium
placed into RAM. This simply means that it has been put in the       III can potentially process 4 bytes simultaneously, 800 million
computer’s temporary storage area so that the CPU can                times per second (possibly more based on pipelining)! The goal
access that information more easily. The CPU requests the data it    of the memory system is to meet those requirements.
needs from RAM, processes it and writes new data back to RAM
                                                                     A computer’s system RAM alone is not fast enough to match the
in a continuous cycle. In most computers, this shuffling of data
                                                                     speed of the CPU. That is why you need a cache (see the next
between the CPU and RAM happens millions of times every
                                                                     section). However, the faster RAM is, the better. Most chips
second. When an application is closed, it and any accompanying
                                                                     today operate with a cycle rate of 50 to 70 nanoseconds. The
files are usually purged (deleted) from RAM to make room for
                                                                     read/write speed is typically a function of the type of RAM used,
new data. If the changed files are not saved to a permanent
                                                                     such as DRAM, SDRAM, RAMBUS. We will talk about these
storage device before being purged, they are lost.
                                                                     various types of memory later.
                  The Need for Speed                                 System RAM speed is controlled by bus width and bus speed.
One common question about desktop computers that comes up            Bus width refers to the number of bits that can be sent to the
all the time is, “Why does a computer need so many memory            CPU simultaneously, and bus speed refers to the number of times
systems?” A typical computer has:                                    a group of bits can be sent each second. A bus cycle occurs
* Level 1 and level 2 caches                                         every time data travels from memory to the CPU. For example, a
* Normal system RAM                                                  100-MHz 32-bit bus is theoretically capable of sending 4 bytes
* Virtual memory                                                     (32 bits divided by 8 = 4 bytes) of data to the CPU 100 million
* A hard disk                                                        times per second, while a 66-MHz 16-bit bus can send 2 bytes of
                                                                     data 66 million times per second. If you do the math, you’ll find
Why so many? The answer to this question can teach you a lot         that simply changing the bus width from 16 bits to 32 bits and the
about memory!                                                        speed from 66 MHz to 100 MHz in our example allows for three
                                                                     times as much data (400 million bytes versus 132 million bytes) to
                                                                     pass through to the CPU every second.

Fast, powerful CPUs need quick and easy access to large
amounts of data in order to maximize their performance. If the
CPU cannot get to the data it needs, it literally stops and waits
for it. Modern CPUs running at speeds of about 1 gigahertz can
consume massive amounts of data - potentially billions of bytes
per second. The problem that computer designers face is that
memory that can keep up with a 1-gigahertz CPU is extremely          In reality, RAM doesn’t usually operate at optimum speed.
expensive - much more expensive than anyone can afford in large      Latency changes the equation radically. Latency refers to the
quantities.                                                          number of clock cycles needed to read a bit of information. For
Computer designers have solved the cost problem by “tiering”         example, RAM rated at 100 MHz is capable of sending a bit in
memory - using expensive memory in small quantities and then         0.00000001 seconds, but may take 0.00000005 seconds to start the
backing it up with larger quantities of less expensive memory.       read process for the first bit. To compensate for latency, CPUs
                                                                     uses a special technique called burst mode.
The cheapest form of read/write memory in wide use today is the
hard disk. Hard disks provide large quantities of inexpensive,       Burst mode depends on the expectation that data requested by
permanent storage. You can buy hard disk space for pennies per       the CPU will be stored in sequential memory cells. The memory
megabyte, but it can take a good bit of time (approaching a          controller anticipates that whatever the CPU is working on will
second) to read a megabyte off a hard disk. Because storage          continue to come from this same series of memory addresses, so
space on a hard disk is so cheap and plentiful, it forms the final   it reads several consecutive bits of data together. This means
stage of a CPUs memory hierarchy, called virtual memory.             that only the first bit is subject to the full effect of latency;
                                                                     reading successive bits takes significantly less time. The rated
The next level of the hierarchy is RAM. We discuss RAM in            burst mode of memory is normally expressed as four numbers
detail in How RAM Works, but several points about RAM are            separated by dashes. The first number tells you the number of
important here.                                                      clock cycles needed to begin a read operation; the second, third
The bit size of a CPU tells you how many bytes of information it     and fourth numbers tell you how many cycles are needed to read
can access from RAM at the same time. For example, a 16-bit CPU      each consecutive bit in the row, also known as the wordline. For
                                                                  Page 59
example: 5-1-1-1 tells you that it takes five cycles to read the first   switches, or flip-flops, between two states. This means that it
bit and one cycle for each bit after that. Obviously, the lower          does not have to be continually refreshed like DRAM. Each cell
these numbers are, the better the performance of the memory.             will maintain its data as long as it has power. Without the need
                                                                         for constant refreshing, SRAM can operate extremely quickly.
Burst mode is often used in conjunction with pipelining, another
                                                                         But the complexity of each cell make it prohibitively expensive for
means of minimizing the effects of latency. Pipelining organizes
                                                                         use as standard RAM.
data retrieval into a sort of assembly-line process. The memory
controller simultaneously reads one or more words from memory,           The SRAM in the cache can be asynchronous or synchronous.
sends the current word or words to the CPU and writes one or             Synchronous SRAM is designed to exactly match the speed of
more words to memory cells. Used together, burst mode and                the CPU, while asynchronous is not. That little bit of timing
pipelining can dramatically reduce the lag caused by latency.            makes a difference in performance. Matching the CPU’s clock
                                                                         speed is a good thing, so always look for synchronized SRAM.
So why wouldn’t you buy the fastest, widest memory you can
                                                                         (For more information on the various types of RAM, see How
get? The speed and width of the memory’s bus should match the
                                                                         RAM Works.)
system’s bus. You can use memory designed to work at 100 MHz
in a 66-MHz system, but it will run at the 66-MHz speed of the           The final step in memory is the registers. These are memory cells
bus so there is no advantage, and 32-bit memory won’t fit on a           built right into the CPU that contain specific data needed by the
16-bit bus.                                                              CPU, particularly the arithmetic and logic unit (ALU). An integral
                                                                         part of the CPU itself, they are controlled directly by the compiler
                   Cache and Registers                                   that sends information for the CPU to process. See How Micro-
Even with a wide and fast bus, it still takes longer for data to get     processors Work for details on registers.
from the memory card to the CPU than it takes for the CPU to
                                                                                              Types of Memory
actually process the data. Caches are designed to alleviate this
bottleneck by making the data used most often by the CPU                 Memory can be split into two main categories: volatile and
instantly available. This is accomplished by building a small            nonvolatile. Volatile memory loses any data as soon as the
amount of memory, known as primary or level 1 cache, right into          system is turned off; it requires constant power to remain viable.
the CPU. Level 1 cache is very small, normally ranging between 2         Most types of RAM fall into this category.
kilobytes (KB) and 64 KB.
                                                                         Nonvolatile memory does not lose its data when the system or
                                                                         device is turned off. A number of types of memory fall into this
                                                                         category. The most familiar is ROM, but Flash memory storage
                                                                         devices such as CompactFlash or SmartMedia cards are also
                                                                         forms of nonvolatile memory.
                                                                                        Computer Memory Terms
                                                                         Bit - In the binary system, either a one or a zero. It is the smallest
The secondary or level 2 cache typically resides on a memory             piece of data. Byte – A unit of 8 bits. Kilobit/megabit/gigabit
card located near the CPU. The level 2 cache has a direct                - Used to describe bandwidth speeds. For example, 56Kbps
connection to the CPU. A dedicated integrated circuit on the             means that data is capable of traveling at 56 kilobits per second.
motherboard, the L2 controller, regulates the use of the level 2         Ethernet networks transmit data at either 10Mbps (10 megabits
cache by the CPU. Depending on the CPU, the size of the level 2          per second) or 100Mbps (100 megabits per second). Kilobyte -
cache ranges from 256 KB to 2 megabytes (MB). In most sys-               The standard unit of measurement for file sizes. Megabyte - The
tems, data needed by the CPU is accessed from the cache                  standard unit of measurement for RAM. Gigabyte - The standard
approximately 95 percent of the time, greatly reducing the               unit of measurement for hard drives. Terabyte, exabyte -
overhead needed when the CPU has to wait for data from the               Extremely large storage capacity typically found in enterprise-
main memory.                                                             level operations for large companies. RAM - Random access
                                                                         memory is fast, temporary storage for your computer. ROM –
                                                                         Read-only memory is fast, permanent storage for your computer.
Some inexpensive systems dispense with the level 2 cache                 Flash memory - A type of ROM that can be altered quickly and
altogether. Many high performance CPUs now have the level 2              without special tools. BIOS - Flash memory inside your
cache actually built into the CPU chip itself. Therefore, the size of    computer that provides the necessary information for your
the level 2 cache and whether it is onboard (on the CPU) is a            computer to work. Hertz - Unit of measurement that list the
major determining factor in the performance of a CPU. For more           number of times a device cycles through a process per second.
details on caching, see How Caching Works.                               Kilohertz - Unit of measurement equal to 1,000 hertz or 1,000
                                                                         cycles per second. Megahertz - Unit of measurement equal to
A particular type of RAM, static random access memory                    1,000 kilohertz or 1,000,000 cycles per second. Nanosecond - One
(SRAM), is used primarily for cache. SRAM uses multiple                  billionth of a second. Used to measure the speed of memory
transistors, typically four to six, for each memory cell. It has an      chips.
external gate array known as a bistable multivibrator that
                                                               Page 60
                                                                                 A Simple Example: After Cache
         Good Boot Guide to Caching
                                                                       Let’s give the librarian a backpack into which he will be able to
                                                                       store 10 books (in computer terms, the librarian now has a 10-
                                                                       book cache). In this backpack, he will put the books the clients
                                                                       return to him, up to a maximum of 10. Let’s use the prior example,
                                                                       but now with our new-and-improved caching librarian.
                                                                       The day starts. The backpack of the librarian is empty. Our first
                                                                       client arrives and asks for Moby Dick. No magic here — the
                                                                       librarian has to go to the storeroom to get the book. He gives it to
                                                                       the client. Later, the client returns and gives the book back to the
                                                                       librarian. Instead of returning to the storeroom to return the book,
                                                                       the librarian puts the book in his backpack and stands there (he
                                                                       checks first to see if the bag is full — more on that later). Another
                                                                       client arrives and asks for Moby Dick. Before going to the
                                                                       storeroom, the librarian checks to see if this title is in his back-
If you have been shopping for a computer, then you have heard          pack. He finds it! All he has to do is take the book from the
the word “cache.” Modern computers have both L1 and L2                 backpack and give it to the client. There’s no journey into the
caches. You may also have gotten advice on the topic from well-        storeroom, so the client is served more efficiently.
meaning friends, perhaps something like “Don’t buy that Celeron
                                                                       What if the client asked for a title not in the cache (the back-
chip, it doesn’t have any cache in it!”
                                                                       pack)? In this case, the librarian is less efficient with a cache than
It turns out that caching is an important computer-science             without one, because the librarian takes the time to look for the
process that appears on every computer in a variety of forms.          book in his backpack first. One of the challenges of cache design
There are memory caches, hardware and software disk caches,            is to minimize the impact of cache searches, and modern hardware
page caches and more. Virtual memory is even a form of caching.        has reduced this time delay to practically zero. Even in our simple
In this article, we will explore caching so you can understand         librarian example, the latency time (the waiting time) of searching
why it is so important.                                                the cache is so small compared to the time to walk back to the
                                                                       storeroom that it is irrelevant. The cache is small (10 books), and
         A Simple Example: Before Cache                                the time it takes to notice a miss is only a tiny fraction of the time
Caching is a technology based on the memory subsystem of               that a journey to the storeroom takes.
your computer. The main purpose of a cache is to accelerate your       From this example you can see several important facts about
computer while keeping the price of the computer low. Caching          caching:
allows you to do your computer tasks more rapidly.
                                                                       * Cache technology is the use of a faster but smaller memory
To understand the basic idea behind a cache system, let’s start          type to accelerate a slower but larger memory type.
with a super-simple example that uses a librarian to demonstrate       * When using a cache, you must check the cache to see if an
caching concepts. Let’s imagine a librarian behind his desk. He is       item is in there. If it is there, it’s called a cache hit. If not, it is
there to give you the books you ask for. For the sake of simplic-        called a cache miss and the computer must wait for a round trip
ity, let’s say you can’t get the books yourself - you have to ask       from the larger, slower memory area.
the librarian for any book you want to read, and he fetches it for     * A cache has some maximum size that is much smaller than the
you from a set of stacks in a storeroom (the library of congress in      larger storage area.
Washington, D.C., is set up this way). First, let’s start with a       * It is possible to have multiple layers of cache. With our librarian
librarian without cache.                                                 example, the smaller but faster memory type is the backpack,
                                                                         and the storeroom represents the larger and slower memory
The first customer arrives. He asks for the book Moby Dick. The
                                                                         type. This is a one-level cache. There might be another layer of
librarian goes into the storeroom, gets the book, returns to the
                                                                         cache consisting of a shelf that can hold 100 books behind the
counter and gives the book to the customer. Later, the client
                                                                         counter. The librarian can check the backpack, then the shelf
comes back to return the book. The librarian takes the book and
                                                                         and then the storeroom. This would be a two-level cache.
returns it to the storeroom. He then returns to his counter waiting
for another customer. Let’s say the next customer asks for Moby                               Computer Caches
Dick (you saw it coming...). The librarian then has to return to the
storeroom to get the book he recently handled and give it to the       A computer is a machine in which we measure time in very small
client. Under this model, the librarian has to make a complete         increments. When the microprocessor accesses the main memory
round trip to fetch every book - even very popular ones that are       (RAM), it does it in about 60 nanoseconds (60 billionths of a
requested frequently. Is there a way to improve the performance        second). That’s pretty fast, but it is much slower than the typical
of the librarian?                                                      microprocessor. Microprocessors can have cycle times as short
                                                                       as 2 nanoseconds, so to a microprocessor 60 nanoseconds
Yes, there’s a way - we can put a cache on the librarian. In the       seems like an eternity.
next section, we’ll look at this same example but this time, the
librarian will use a caching system.
                                                                   Page 61
What if we build a special memory bank in the motherboard, small           you won’t wait. The operating system checked into its memory
but very fast (around 30 nanoseconds)? That’s already two times            cache for the floppy disk and found what it was looking for. So
faster than the main memory access. That’s called a level 2 cache          instead of waiting 20 seconds, the data was found in a memory
or an L2 cache. What if we build an even smaller but faster                subsystem much faster than when you first tried it (one access to
memory system directly into the microprocessor’s chip? That                the floppy disk takes 120 milliseconds, while one access to the
way, this memory will be accessed at the speed of the micropro-            main memory takes around 60 nanoseconds — that’s a lot faster).
cessor and not the speed of the memory bus. That’s an L1 cache,            You could have run the same test on your hard disk, but it’s more
which on a 233-megahertz (MHz) Pentium is 3.5 times faster than            evident on the floppy drive because it’s so slow.
the L2 cache, which is two times faster than the access to main
                                                                           To give you the big picture of it all, here’s a list of a normal
                                                                           caching system:
Some microprocessors have two levels of cache built right into             * L1 cache - Memory accesses at full microprocessor speed (10
the chip. In this case, the motherboard cache — the cache that               nanoseconds, 4 kilobytes to 16 kilobytes in size)
exists between the microprocessor and main system memory —                 * L2 cache - Memory access of type SRAM (around 20 to 30
becomes level 3, or L3 cache.                                                nanoseconds, 128 kilobytes to 512 kilobytes in size)
There are a lot of subsystems in a computer; you can put cache             * Main memory - Memory access of type RAM (around 60
between many of them to improve performance. Here’s an                       nanoseconds, 32 megabytes to 128 megabytes in size)
example. We have the microprocessor (the fastest thing in the              * Hard disk - Mechanical, slow (around 12 milliseconds,
computer). Then there’s the L1 cache that caches the L2 cache                1 gigabyte to 10 gigabytes in size)
that caches the main memory which can be used (and is often                * Internet - Incredibly slow (between 1 second and 3 days,
used) as a cache for even slower peripherals like hard disks and             unlimited size)
CD-ROMs. The hard disks are also used to cache an even slower              As you can see, the L1 cache caches the L2 cache, which caches
medium - your Internet connection.                                         the main memory, which can be used to cache the disk sub-
                    Caching Subsystems                                     systems, and so on.

Your Internet connection is the slowest link in your computer. So                              Cache Technology
your browser (Internet Explorer, Netscape, Opera, etc.) uses the           One common question asked at this point is, “Why not make all
hard disk to store HTML pages, putting them into a special folder          of the computer’s memory run at the same speed as the L1 cache,
on your disk. The first time you ask for an HTML page, your                so no caching would be required?” That would work, but it
browser renders it and a copy of it is also stored on your disk.           would be incredibly expensive. The idea behind caching is to use
The next time you request access to this page, your browser                a small amount of expensive memory to speed up a large amount
checks if the date of the file on the Internet is newer than the one       of slower, less-expensive memory.
cached. If the date is the same, your browser uses the one on
your hard disk instead of downloading it from Internet. In this            In designing a computer, the goal is to allow the microprocessor
case, the smaller but faster memory system is your hard disk and           to run at its full speed as inexpensively as possible. A 500-MHz
the larger and slower one is the Internet.                                 chip goes through 500 million cycles in one second (one cycle
                                                                           every two nanoseconds). Without L1 and L2 caches, an access
Cache can also be built directly on peripherals. Modern hard               to the main memory takes 60 nanoseconds, or about 30 wasted
disks come with fast memory, around 512 kilobytes, hardwired to            cycles accessing memory.
the hard disk. The computer doesn’t directly use this memory —
the hard-disk controller does. For the computer, these memory              When you think about it, it is kind of incredible that such
chips are the disk itself. When the computer asks for data from            relatively tiny amounts of memory can maximize the use of much
the hard disk, the hard-disk controller checks into this memory            larger amounts of memory. Think about a 256-kilobyte L2 cache
before moving the mechanical parts of the hard disk (which is              that caches 64 megabytes of RAM. In this case, 256,000 bytes
very slow compared to memory). If it finds the data that the               efficiently caches 64,000,000 bytes. Why does that work?
computer asked for in the cache, it will return the data stored in         In computer science, we have a theoretical concept called locality
the cache without actually accessing data on the disk itself,              of reference. It means that in a fairly large program, only small
saving a lot of time.                                                      portions are ever used at any one time. As strange as it may
Here’s an experiment you can try. Your computer caches your                seem, locality of reference works for the huge majority of
floppy drive with main memory, and you can actually see it                 programs. Even if the executable is 10 megabytes in size, only a
happening. Access a large file from your floppy — for example,             handful of bytes from that program are in use at any one time,
open a 300-kilobyte text file in a text editor. The first time, you will   and their rate of repetition is very high. On the next page, you’ll
see the light on your floppy turning on, and you will wait. The            learn more about locality of reference.
floppy disk is extremely slow, so it will take 20 seconds to load                           Locality of Reference
the file. Now, close the editor and open the same file again. The
second time (don’t wait 30 minutes or do a lot of disk access              Let’s take a look at the following pseudo-code to see why locality
between the two tries) you won’t see the light turning on, and             of reference works (see How C Programming Works to really get
                                                                           into it):
                                                                  Page 62
Output to screen « Enter a number between 1 and                          popular. In fact, FDDs have been an key component of most
100 »                                                                    personal computers for more than 20 years.
Read input from user
                                                                         Basically, a floppy disk drive reads and writes data to a small,
Put value from user in variable X
                                                                         circular piece of metal-coated plastic similar to audio cassette
Put value 100 in variable Y
                                                                         tape. In this article, you will learn more about what is inside a
Put value 1 in variable Z
                                                                         floppy disk drive and how it works. You will also find out some
Loop Y number of time
                                                                         cool facts about FDDs.
  Divide Z by X
  If the remainder of the division = 0                                            History of the Floppy Disk Drive
     then output « Z is a multiple of X »
   Add 1 to Z                                                            The floppy disk drive (FDD) was invented at IBM by Alan
Return to loop                                                           Shugart in 1967. The first floppy drives used an 8-inch disk (later
End                                                                      called a “diskette” as it got smaller), which evolved into the 5.25-
                                                                         inch disk that was used on the first IBM Personal Computer in
This small program asks the user to enter a number between 1             August 1981. The 5.25-inch disk held 360 kilobytes compared to
and 100. It reads the value entered by the user. Then, the program       the 1.44 megabyte capacity of today’s 3.5-inch diskette.
divides every number between 1 and 100 by the number entered
by the user. It checks if the remainder is 0 (modulo division). If       The 5.25-inch disks were dubbed “floppy” because the diskette
so, the program outputs “Z is a multiple of X” (for example, 12 is       packaging was a very flexible plastic envelope, unlike the rigid
a multiple of 6), for every number between 1 and 100. Then the           case used to hold today’s 3.5-inch diskettes.
program ends.                                                            By the mid-1980s, the improved designs of the read/write heads,
Even if you don’t know much about computer programming, it is            along with improvements in the magnetic recording media, led to
easy to understand that in the 11 lines of this program, the loop        the less-flexible, 3.5-inch, 1.44-megabyte (MB) capacity FDD in
part (lines 7 to 9) are executed 100 times. All of the other lines are   use today. For a few years, computers had both FDD sizes (3.5-
executed only once. Lines 7 to 9 will run significantly faster           inch and 5.25-inch). But by the mid-1990s, the 5.25-inch version
because of caching.                                                      had fallen out of popularity, partly because the diskette’s
                                                                         recording surface could easily become contaminated by finger-
This program is very small and can easily fit entirely in the            prints through the open access area.
smallest of L1 caches, but let’s say this program is huge. The
result remains the same. When you program, a lot of action takes                     Parts of a Floppy Disk Drive
place inside loops. A word processor spends 95 percent of the                         Floppy Disk Drive Terminology
time waiting for your input and displaying it on the screen. This
part of the word-processor program is in the cache.                      Floppy disk - Also called diskette. The common size is 3.5 inches.
                                                                         Floppy disk drive - The electromechanical device that reads and
This 95%-to-5% ratio (approximately) is what we call the locality         writes floppy disks.
of reference, and it’s why a cache works so efficiently. This is         Track - Concentric ring of data on a side of a disk.
also why such a small cache can efficiently cache such a large           Sector - A subset of a track, similar to wedge or a slice of pie.
memory system. You can see why it’s not worth it to construct a
computer with the fastest memory everywhere. We can deliver 95                                       The Disk
percent of this effectiveness for a fraction of the cost.
                                                                         A floppy disk is a lot like a cassette tape:

            Good Boot Guide to Your
                                                                         * Both use a thin plastic base material coated with iron oxide.
                                                                          This oxide is a ferromagnetic material, meaning that if you
               Floppy Disk Drive                                           expose it to a magnetic field it is permanently magnetized by the
                                                                         * Both can record information instantly.
                                                                         * Both can be erased and reused many times.
                                                                         * Both are very inexpensive and easy to use.
                                                                         If you have ever used an audio cassette, you know that it has
                                                                         one big disadvantage — it is a sequential device. The tape has a
                                                                         beginning and an end, and to move the tape to another song later
                                                                         in the sequence of songs on the tape you have to use the fast
                                                                         forward and rewind buttons to find the start of the song, since
                                                                         the tape heads are stationary. For a long audio cassette tape it
                                                                         can take a minute or two to rewind the whole tape, making it hard
If you have spent any time at all working with a computer, then          to find a song in the middle of the tape.
chances are good that you have used a floppy disk at some
                                                                         A floppy disk, like a cassette tape, is made from a thin piece of
point. The floppy disk drive (FDD) was the primary means of
                                                                         plastic coated with a magnetic material on both sides. However, it
adding data to a computer until the CD-ROM drive became
                                                                Page 63
is shaped like a disk rather than a long thin ribbon. The tracks are    The read/write heads do not touch the diskette media when the
arranged in concentric rings so that the software can jump from         heads are traveling between tracks. Electronic optics check for
“file 1” to “file 19” without having to fast forward through files 2-   the presence of an opening in the lower corner of a 3.5-inch
18. The diskette spins like a record and the heads move to the          diskette (or a notch in the side of a 5.25-inch diskette) to see if
correct track, providing what is known as direct access storage.        the user wants to prevent data from being written on it.

In the illustration above, you can see how the disk is
divided into tracks (brown) and sectors (yellow).

                           The Drive
The major parts of a FDD include:
* Read/Write Heads: Located on both sides of a diskette, they                 Read/write heads for each side of the diskette
   move together on the same assembly. The heads are not
  directly opposite each other in an effort to prevent interaction
                                                                                   Writing Data on a Floppy Disk
  between write operations on each of the two media surfaces.           The following is an overview of how a floppy disk drive writes
  The same head is used for reading and writing, while a second,        data to a floppy disk. Reading data is very similar. Here’s what
  wider head is used for erasing a track just prior to it being         happens:
  written. This allows the data to be written on a wider “clean         1. The computer program passes an instruction to the computer
  slate,” without interfering with the analog data on an adjacent          hardware to write a data file on a floppy disk, which is very
  track.                                                                  similar to a single platter in a hard disk drive except that it is
* Drive Motor: A very small spindle motor engages the metal                spinning much slower, with far less capacity and slower access
  hub at the center of the diskette, spinning it at either 300 or 360     time.
  rotations per minute (RPM).                                           2. The computer hardware and the floppy-disk-drive controller
* Stepper Motor: This motor makes a precise number of                      start the motor in the diskette drive to spin the floppy disk.
   stepped revolutions to move the read/write head assembly to
  the proper track position. The read/write head assembly is               The disk has many concentric tracks on each side. Each track
   fastened to the stepper motor shaft.                                    is divided into smaller segments called sectors, like slices of a
* Mechanical Frame: A system of levers that opens the little
  protective window on the diskette to allow the read/write             3. A second motor, called a stepper motor, rotates a worm-gear
  heads to touch the dual-sided diskette media. An external                shaft (a miniature version of the worm gear in a bench-top vise)
   button allows the diskette to be ejected, at which point the            in minute increments that match the spacing between tracks.
   spring-loaded protective window on the diskette closes.                The time it takes to get to the correct track is called “access
* Circuit Board: Contains all of the electronics to handle the            time.” This stepping action (partial revolutions) of the stepper
  data read from or written to the diskette. It also controls the         motor moves the read/write heads like the jaws of a bench-top
  stepper-motor control circuits used to move the read/write              vise. The floppy-disk-drive electronics know how many steps
  heads to each track, as well as the movement of the read/write          the motor has to turn to move the read/write heads to the
   heads toward the diskette surface.                                     correct track.
                                                                  Page 64
4. The read/write heads stop at the track. The read head checks
   the prewritten address on the formatted diskette to be sure it is          Good Boot Guide to Your Monitor
   using the correct side of the diskette and is at the proper track.
   This operation is very similar to the way a record player
   automatically goes to a certain groove on a vinyl record.
5. Before the data from the program is written to the diskette, an
   erase coil (on the same read/write head assembly) is energized
   to “clear” a wide, “clean slate” sector prior to writing the
   sector data with the write head. The erased sector is wider than
   the written sector - this way, no signals from sectors in
  adjacent tracks will interfere with the sector in the track being
6. The energized write head puts data on the diskette by magne
  tizing minute, iron, bar-magnet particles embedded in the
   diskette surface, very similar to the technology used in the mag
   stripe on the back of a credit card. The magnetized particles
    have their north and south poles oriented in such a way that
    their pattern may be detected and read on a subsequent read
7. The diskette stops spinning. The floppy disk drive waits for
  the next command.
                                                                          A computer display is a marvelous thing. An unassuming dark
On a typical floppy disk drive, the small indicator light stays on        gray surface can suddenly transform into an artist’s canvas, an
during all of the above operations.                                       engineer’s gauges, a writer’s page or your very own window to
                Floppy Disk Drive Facts                                   both the real world and a huge range of artificial worlds!
                                                                          Because we use them daily, many of us have a lot of questions
Here are some interesting things to note about FDDs:
                                                                          about our displays and may not even realize it. What does
* Two floppy disks do not get corrupted if they are stored \              “aspect ratio” mean? What is dot pitch? How much power does a
  together, due to the low level of magnetism in each one.                display use? What is the difference between CRT and LCD?
* In your PC, there is a twist in the FDD data-ribbon cable - this        What does “refresh rate” mean?
  twist tells the computer whether the drive is an A-drive or a B-
  drive.                                                                  In this Chapter, we will answer all of these questions and many
* Like many household appliances, there are really no serviceable         more. By the end of the article, you will be able to understand
  parts in today’s FDDs. This is because the cost of a new drive          your current display and also make better decisions when
  is considerably less than the hourly rate typically charged to          purchasing your next one.
  disassemble and repair a drive.                                                                  The Basics
* If you wish to redisplay the data on a diskette drive after
  changing a diskette, you can simply tap the F5 key (in most             Often referred to as a monitor when packaged in a separate case,
  Windows applications).                                                  the display is the most-used output device on a computer. The
* In the corner of every 3.5-inch diskette, there is a small slider. If   display provides instant feedback by showing you text and
  you uncover the hole by moving the slider, you have protected           graphic images as you work or play. Most desktop displays use a
  the data on the diskette from being written over or erased.             cathode ray tube (CRT), while portable computing devices such
* Floppy disks, while rarely used to distribute software (as in the       as laptops incorporate liquid crystal display (LCD), light-emitting
  past), are still used in these applications:                            diode (LED), gas plasma or other image projection technology.
  * in some Sony digital cameras                                          Because of their slimmer design and smaller energy consumption,
  * for software recovery after a system crash or a virus attack          monitors using LCD technologies are beginning to replace the
    when data from one computer is needed on a second com-                venerable CRT on many desktops.
    puter and the two computers are not networked
                                                                          When purchasing a display, you have a number of decisions to
  * in bootable diskettes used for updating the BIOS on a
                                                                          make. These decisions affect how well your display will perform
    personal computer in high-density form, used in the popular
                                                                          for you, how much it will cost and how much information you will
    Zip drive
                                                                          be able to view with it. Your decisions include:
                                                                          * Display technology - Currently, the choices are mainly between
                                                                          CRT and LCD technologies.
                                                                          * Cable technology - VGA and DVI are the two most common.
                                                                          Viewable area (usually measured diagonally)
                                                                          * Aspect ratio and orientation (landscape or portrait)
                                                                          * Maximum resolution
                                                                Page 65
* Dot pitch                                                             convert it to analog data for the display scanning mechanism. In
* Refresh rate                                                          the following section, we’ll discuss what happens once the
* Color depth                                                           analog data is ready for transmission.
* Amount of power consumption
                                                                        Display TEchnologies: VGA
In the following sections we will talk about each of these areas so
                                                                        Once the display information is in analog form, it is sent to the
that you can completely understand how your monitor works!
                                                                        monitor through a VGA cable. See the diagram below:
           Display Technology Background
Displays have come a long way since the blinking green monitors
in text-based computer systems of the 1970s. Just look at the
advances made by IBM over the course of a decade:
* In 1981, IBM introduced the Color Graphics Adapter (CGA),
  which was capable of rendering four colors, and had a maximum
  resolution of 320 pixels horizontally by 200 pixels vertically.
* IBM introduced the Enhanced Graphics Adapter (EGA) display
  in 1984. EGA allowed up to 16 different colors and increased the
  resolution to 640x350 pixels, improving the appearance of the
  display and making it easier to read text.
* In 1987, IBM introduced the Video Graphics Array (VGA)
   display system. Most computers today support the VGA
  standard and many VGA monitors are still in use.
* IBM introduced the Extended Graphics Array (XGA) display in
  1990, offering 800x600 pixel resolution in true color (16.8 million
  colors) and 1,024x768 resolution in 65,536 colors.
                 Multi-scanning Monitors
If you have been around computers for more than a decade, then
you probably remember when NEC announced the MultiSync
monitor. Up to that point, most monitors only understood one
frequency, which meant that the monitor operated at a single
fixed resolution and refresh rate. You had to match your monitor
with a graphics adapter that provided that exact signal or it
wouldn’t work.
The introduction of NEC MultiSync technology started a trend
towards multi-scanning monitors. This technology allows a               You can see that a VGA connector like this has three separate
monitor to understand any frequency sent to it within a certain         lines for the red, green and blue color signals, and two lines for
bandwidth. The benefit of a multi-scanning monitor is that you          horizontal and vertical sync signals. In a normal television, all of
can change resolutions and refresh rates without having to              these signals are combined into a single composite video signal.
purchase and install a new graphics adapter or monitor each time.       The separation of the signals is one reason why a computer
Because of the obvious advantage of this approach, nearly every         monitor can have so many more pixels than a TV set.
monitor you buy today is a multi-scanning monitor.                      Since today’s VGA adapters do not fully support the use of
Most displays sold today support the Ultra Extended Graphics            digital monitors, a new standard, Digital Video Interface (DVI) has
Array (UXGA) standard. In the next section, you’ll learn about          been designed for this purpose.
UXGA.                                                                                  Display Technology: DVI
              Display Technology: UXGA                                  Because VGA technology requires that the signal be converted
UXGA can support a palette of up to 16.8 million colors and             from digital to analog for transmission to the monitor, a certain
resolutions of up to 1600x1200 pixels, depending on the video           amount of degradation occurs. DVI keeps data in digital form
memory of the graphics card in your computer. The maximum               from the computer to the monitor, virtually eliminating signal loss.
resolution normally depends on the number of colors displayed.          The DVI specification is based on Silicon Image’s Transition
For example, your card might require that you choose between            Minimized Differential Signaling (TMDS) and provides a high-
16.8 million colors at 800x600, or 65,536 colors at 1600x1200.          speed digital interface. TMDS takes the signal from the graphics
A typical UXGA adapter takes the digital data sent by application       adapter, determines the resolution and refresh rate that the
programs, stores it in video random access memory (VRAM) or             monitor is using and spreads the signal out over the available
some equivalent, and uses a digital-to-analog converter (DAC) to        bandwidth to optimize the data transfer from computer to monitor.
                                                                  Page 66
DVI is technology-independent. Essentially, this means that DVI
is going to perform properly with any display and graphics card
that is DVI compliant. If you buy a DVI monitor, make sure that
you have a video adapter card that can connect to it.
                       Viewable Area
Two measures describe the size of your display: the aspect ratio
and the screen size. Most computer displays, like most televi-
sions, have an aspect ratio of 4:3 right now. This means that the
ratio of the width of the display screen to the height is 4 to 3. The
other aspect ratio in common use is 16:9. Used in cinematic film,
16:9 was not adopted when the television was first developed,
but has always been common in the manufacture of alternative
display technologies such as LCD. With widescreen DVD movies
steadily increasing in popularity, most TV manufacturers now
offer 16:9 displays.
The display includes a projection surface, commonly referred to
as the screen. Screen sizes are normally measured in inches from
one corner to the corner diagonally across from it. This diagonal
measuring system actually came about because the early
television manufacturers wanted to make the screen size of their
TVs sound more impressive. Because the listed size is measured
from the inside beveled edges of the display casing, make sure
                                                                                     See What does .28 dot pitch mean?
you ask what the viewable screen size is. This will usually be
somewhat less than the stated screen size.                                                      Refresh Rate
Popular screen sizes are 15, 17, 19 and 21 inches. Notebook             In monitors based on CRT technology, the refresh rate is the
screen sizes are usually somewhat smaller, typically ranging from       number of times that the image on the display is drawn each
12 to 15 inches. Obviously, the size of the display will directly       second. If your CRT monitor has a refresh rate of 72 Hertz (Hz),
affect resolution. The same pixel resolution will be sharper on a       then it cycles through all the pixels from top to bottom 72 times a
smaller monitor and fuzzier on a larger monitor because the same        second. Refresh rates are very important because they control
number of pixels is being spread out over a larger number of            flicker, and you want the refresh rate as high as possible. Too few
inches. An image on a 21-inch monitor with a 640x480 resolution         cycles per second and you will notice a flickering, which can lead
will not appear nearly as sharp as it would on a 15-inch display at     to headaches and eye strain.
                                                                        Televisions have a lower refresh rate than most computer
        Maximum Resolution and Dot Pitch                                monitors. To help adjust for the lower rate, they use a method
                                                                        called interlacing. This means that the electron gun in the
Resolution refers to the number of individual dots of color,
                                                                        television’s CRT will scan through all the odd rows from top to
known as pixels, contained on a display. Resolution is typically
                                                                        bottom, then start again with the even rows. The phosphors hold
expressed by identifying the number of pixels on the horizontal
                                                                        the light long enough that your eyes are tricked into thinking that
axis (rows) and the number on the vertical axis (columns), such as
                                                                        all the lines are being drawn together.
640x480. The monitor’s viewable area (discussed in the previous
section), refresh rate and dot pitch all directly affect the maximum    Because your monitor’s refresh rate depends on the number of
resolution a monitor can display.                                       rows it has to scan, it limits the maximum possible resolution. A
                                                                        lot of monitors support multiple refresh rates, usually dependent
                           Dot Pitch                                    on the resolution you have chosen. Keep in mind that there is a
Briefly, the dot pitch is the measure of how much space there is        tradeoff between flicker and resolution, and then pick what works
between a display’s pixels. When considering dot pitch, remem-          best for you. (See Figure top of Column 1, Page 68).
ber that smaller is better. Packing the pixels closer together is
fundamental to achieving higher resolutions.
                                                                                                Color Depth
A display normally can support resolutions that match the               The combination of the display modes supported by your
physical dot (pixel) size as well as several lesser resolutions. For    graphics adapter and the color capability of your monitor
example, a display with a physical grid of 1280 rows by 1024            determine how many colors can be displayed. For example, a
columns can obviously support a maximum resolution of                   display that can operate in SuperVGA (SVGA) mode can display
1280x1024 pixels. It usually also supports lower resolutions such       up to 16,777,216 (usually rounded to 16.8 million) colors because
as 1024x768, 800x600, and 640x480.                                      it can process a 24-bit-long description of a pixel. The number of
                                                                        bits used to describe a pixel is known as its bit depth.
                                                              Page 67
                                                                      You will notice that the last entry in the chart is for 32 bits. This
                                                                      is a special graphics mode used by digital video, animation and
                                                                      video games to achieve certain effects. Essentially, 24 bits are
                                                                      used for color and the other 8 bits are used as a separate layer for
                                                                      representing levels of translucency in an object or image.
                                                                      Nearly every monitor sold today can handle 24-bit color using a
                                                                      standard VGA connector, as discussed previously.
                                                                                          Power Consumption
                                                                      Power consumption varies greatly with different technologies.
                                                                      CRTs are somewhat power-hungry, at about 110 watts for a
                                                                      typical display, especially when compared to LCDs, which
                                                                      average between 30 and 40 watts.
                                                                      In a typical home computer setup with a CRT-based display, the
                                                                      monitor accounts for over 80 percent of the electricity used!
                                                                      Because most users don’t interact with the computer much of the
                                                                      time it is on, the U.S. government initiated the Energy Star
                                                                      program in 1992. Energy Star-compliant equipment monitors user
                                                                      activity and suspends non-critical processes, such as maintain-
                                                                      ing a visual display, until you move the mouse or tap the
                                                                      keyboard. According to the EPA, if you use a computer system
                                                                      that is Energy Star compliant, it could save you approximately
                                                                      $400 a year on your electric bill! Similarly, because of the differ-
With a 24-bit bit depth, 8 bits are dedicated to each of the three    ence in power usage, an LCD monitor might cost more upfront
additive primary colors - red, green and blue. This bit depth is      but end up saving you money in the long run.
also called true color because it can produce the 10,000,000
colors discernible to the human eye, while a 16-bit display is only                Monitor Trends: Flat Panels
capable of producing 65,536 colors. Displays jumped from 16-bit       CRT technology is still the most prevalent system in desktop
color to 24-bit color because working in 8-bit increments makes       displays. Because standard CRT technology requires a certain
things a whole lot easier for developers and programmers.             distance between the beam projection device and the screen,
Simply put, color bit depth refers to the number of bits used to      monitors employing this type of display technology tend to be
describe the color of a single pixel. The bit depth determines the    very bulky. Other technologies make it possible to have much
number of colors that can be displayed at one time. Take a look at    thinner displays, commonly known as flat-panel displays.
the following chart to see the number of colors different bit
depths can produce:

                                                                                           Sony flat-panel display
                                                                      Liquid crystal display (LCD) technology works by blocking light
                                                                      rather than creating it, while light-emitting diode (LED) and gas
                                                                      plasma work by lighting up display screen positions based on
                                                                      the voltages at different grid intersections. LCDs require far less
                                                                      energy than LED and gas plasma technologies and are currently
                                                                      the primary technology for notebook and other mobile comput-
                                                                      ers. As flat-panel displays continue to grow in screen size and
                                                                      improve in resolution and affordability, they will gradually replace
                                                                      CRT-based displays.
                                                                Page 68
                                                                                            Inside a Mouse
     Good Boot Guide to Your Mouse
                                                                      The main goal of any mouse is to translate the motion of your
                                                                      hand into signals that the computer can use. Almost all mice
                                                                      today do the translation using five components:

Mice come in all shapes and sizes. This is an older
two-button mouse.
 Mice first broke onto the public stage with the introduction of
the Apple Macintosh in 1984, and since then they have helped to
completely redefine the way we use computers.
Every day of your computing life, you reach out for your mouse                             The guts of a mouse
whenever you want to move your cursor or activate something.
Your mouse senses your motion and your clicks and sends them          1. A ball inside the mouse touches the desktop and rolls when the
to the computer so it can respond appropriately.                         mouse moves.
In this Chapter, we’ll take the cover off of this important part of
the human-machine interface and see exactly what makes it tick!
It is amazing how simple and effective a mouse is, and it is also
amazing how long it took mice to become a part of everyday life.
Given that people naturally point at things - usually before they
speak - it is surprising that it took so long for a good pointing
device to develop. Although originally conceived in the 1960s, it
took quite some time for mice to become mainstream.
In the beginning there was no need to point because computers
used crude interfaces like teletype machines or punch cards for
data entry. The early text terminals did nothing more than emulate
a teletype (using the screen to replace paper), so it was many
years (well into the 1960s and early 1970s) before arrow keys
were found on most terminals. Full screen editors were the first
things to take real advantage of the cursor keys, and they offered    The underside of the mouse’s logic board: The
humans the first crude way to point.                                  exposed portion of the ball touches the desktop.
Light pens were used on a variety of machines as a pointing           2. Two rollers inside the mouse touch the ball. One of the rollers
device for many years, and graphics tablets, joy sticks and              is oriented so that it detects motion in the X direction, and the
various other devices were also popular in the 1970s. None of            other is oriented 90 degrees to the first roller so it detects
these really took off as the pointing device of choice, however.         motion in the Y direction. When the ball rotates, one or both of
When the mouse hit the scene attached to the Mac, it was an              these rollers rotate as well. The following image shows the two
immediate success. There is something about it that is completely        white rollers on this mouse:
natural. Compared to a graphics tablet, mice are extremely                                                         The rollers that
inexpensive and they take up very little desk space. In the PC                                                     touch the ball and
world, mice took longer to gain ground, mainly because of a lack                                                   detect X and Y
of support in the operating system. Once Windows 3.1 made                                                          motion
Graphical User Interfaces (GUIs) a standard, the mouse became
the PC-human interface of choice very quickly.
                                                                 Page 69
3. The rollers each connect to a shaft, and the shaft spins a disk
   with holes in it. When a roller rolls, its shaft and disk spin. The
  following image shows the disk:

A typical optical encoding disk: This disk has 36
holes around its outer edge.
4. On either side of the disk there is an infrared LED and an
   infrared sensor. The holes in the disk break the beam of light        The logic section of a mouse is dominated by an
   coming from the LED so that the infrared sensor sees pulses of        encoder chip, a small processor that reads the pulses
   light. The rate of the pulsing is directly related to the speed of    coming from the infrared sensors and turns them into
   the mouse and the distance it travels.                                bytes sent to the computer. You can also see the two
                                                                         buttons that detect clicks (on either side of the wire
                                                                         In this optomechanical arrangement, the disk moves mechani-
                                                                         cally, and an optical system counts pulses of light. On this
                                                                         mouse, the ball is 21 mm in diameter. The roller is 7 mm in
                                                                         diameter. The encoding disk has 36 holes. So if the mouse moves
                                                                         25.4 mm (1 inch), the encoder chip detects 41 pulses of light.
                                                                         You might have noticed that each encoder disk has two infrared
                                                                         LEDs and two infrared sensors, one on each side of the disk (so
                                                                         there are four LED/sensor pairs inside a mouse). This arrange-
                                                                         ment allows the processor to detect the disk’s direction of
                                                                         rotation. There is a piece of plastic with a small, precisely located
                                                                         hole that sits between the encoder disk and each infrared sensor.
                                                                         It is visible in this photo:

A close-up of one of the optical encoders that track
mouse motion: There is an infrared LED (clear) on
one side of the disk and an infrared sensor (red) on
the other.
5. An on-board processor chip reads the pulses from the infrared
   sensors and turns them into binary data that the computer can
   understand. The chip sends the binary data to the computer
   through the mouse’s cord.
                                                                Page 70
In the previous figure note the piece of plastic between the            Optical mice have several benefits over wheeled mice:
infrared sensor (red) and the encoding disk.                            * No moving parts means less wear and a lower chance of failure.
This piece of plastic provides a window through which the               * There’s no way for dirt to get inside the mouse and interfere
infrared sensor can “see.” The window on one side of the disk is           with the tracking sensors.
located slightly higher than it is on the other - one-half the height   * Increased tracking resolution means smoother response.
of one of the holes in the encoder disk, to be exact. That differ-      * They don’t require a special surface, such as a mouse pad.
ence causes the two infrared sensors to see pulses of light at          Although LED-based optical mice are fairly recent, another type
slightly different times. There are times when one of the sensors       of optical mouse has been around for over a decade. The original
will see a pulse of light when the other does not, and vice versa.      optical-mouse technology bounced a focused beam of light off a
This page offers a nice explanation of how direction is deter-          highly-reflective mouse pad onto a sensor. The mouse pad had a
mined.                                                                  grid of dark lines. Each time the mouse was moved, the beam of
                     The Optical Mouse                                  light was interrupted by the grid. Whenever the light was
                                                                        interrupted, the sensor sent a signal to the computer and the
With advances it mouse technology, it appears that the venerable        cursor moved a corresponding amount.
wheeled mouse is in danger of extinction. The now-preferred
device for pointing and clicking is the optical mouse.                  This kind of optical mouse was difficult to use, requiring that you
                                                                        hold it at precisely the right angle to ensure that the light beam
                                                                        and sensor aligned. Also, damage to or loss of the mouse pad
                                                                        rendered the mouse useless until a replacement pad was pur-
                                                                        chased. Today’s LED-based optical mice are far more user-
                                                                        friendly and reliable.
                                                                                              Data Interface
                                                                        Most mice in use today use the standard PS/2 type connector, as
                                                                        shown here:

 This Microsoft Intellimouse uses optical technology.
Developed by Agilent Technologies and introduced to the world
in late 1999, the optical mouse actually uses a tiny camera to take
1,500 pictures every second.
Able to work on almost any surface, the mouse has a small, red
light-emitting diode (LED) that bounces light off that surface
onto a complimentary metal-oxide semiconductor (CMOS) sensor.
The CMOS sensor sends each image to a digital signal processor
(DSP) for analysis. The DSP, operating at 18 MIPS (million              A typical PS/2 connector: Assume that pin 1 is
instructions per second), is able to detect patterns in the images      located just to the left of the black alignment pin,
and see how those patterns have moved since the previous                and the others are numbered clockwise from there.
image. Based on the change in patterns over a sequence of               These pins have the following functions (refer to the above
images, the DSP determines how far the mouse has moved and              photo for pin numbering):
sends the corresponding coordinates to the computer. The                1. Unused
computer moves the cursor on the screen based on the coordi-            2. +5 volts (to power the chip and LEDs)
nates received from the mouse. This happens hundreds of times           3. Unused
each second, making the cursor appear to move very smoothly.            4. Clock
                                                 In this photo,         5. Ground
                                                 you can see            6. Data
                                                 the LED on the         Whenever the mouse moves or the user clicks a button, the
                                                 bottom of the          mouse sends 3 bytes of data to the computer. The first byte’s 8
                                                 mouse.                 bits contain:
                                                                        1. Left button state (0 = off, 1 = on)
                                                                        2. Right button state (0 = off, 1 = on)
                                                                        3. 0
                                                               Page 71
4. 1                                                                                     Types of Keyboards
5. X direction (positive or negative)
6. Y direction                                                         Keyboards have changed very little in layout since their intro-
7. X overflow (the mouse moved more than 255 pulses in 1/40th          duction. In fact, the most common change has simply been the
of a second)                                                           natural evolution of adding more keys that provide additional
8. Y overflow                                                          functionality.

The next 2 bytes contain the X and Y movement values, respec-          The most common keyboards are:
tively. These 2 bytes contain the number of pulses that have           * 101-key Enhanced keyboard
been detected in the X and Y direction since the last packet was       * 104-key Windows keyboard
sent.                                                                  Portable computers such as laptops quite often have custom
The data is sent from the mouse to the computer serially on the        keyboards that have slightly different key arrangements than a
data line, with the clock line pulsing to tell the computer where      standard keyboard. Also, many system manufacturers add
each bit starts and stops. Eleven bits are sent for each byte (1       specialty buttons to the standard layout. A typical keyboard has
start bit, 8 data bits, 1 parity bit and 1 stop bit). The PS/2 mouse   four basic types of keys:
sends on the order of 1,200 bits per second. That allows it to         * Typing keys
report mouse position to the computer at a maximum rate of about       * Numeric keypad
40 reports per second. If you are moving the mouse very rapidly,       * Function keys
the mouse may travel an inch or more in one-fortieth of a second.      * Control keys
This is why there is a byte allocated for X and Y motion in the
                                                                       The typing keys are the section of the keyboard that contain the
data protocol.
                                                                       letter keys, generally laid out in the same style that was common
Some mice use serial or USB type connectors.                           for typewriters. This layout, known as QWERTY for the first six
                                                                       letters in the layout, was originally designed to slow down fast
   Good Boot Guide to Your Keyboard                                    typists by making the arrangement of the keys somewhat
                                                                       awkward! The reason that typewriter manufacturers did this was
The part of the computer that we come into most contact with is        because the mechanical arms that imprinted each character on the
probably the piece that we think about the least. But the key-         paper could jam together if the keys were pressed too rapidly.
board is an amazing piece of technology. For instance, did you         Because it has been long established as a standard, and people
know that the keyboard on a typical computer system is actually        have become accustomed to the QWERTY configuration,
a computer itself?                                                     manufacturers developed keyboards for computers using the
                                                                       same layout, even though jamming is no longer an issue. Critics
                                                                       of the QWERTY layout have adopted another layout, Dvorak,
                                                                       that places the most commonly used letters in the most conve-
                                                                       nient arrangement.
                                                                       The numeric keypad is a part of the natural evolution mentioned
                                                                       previously. As the use of computers in business environments
                                                                       increased, so did the need for speedy data entry. Since a large
                                                                       part of the data was numbers, a set of 17 keys was added to the
                                                                       keyboard. These keys are laid out in the same configuration used
                                                                       by most adding machines and calculators, to facilitate the
                                                                       transition to computer for clerks accustomed to these other
                                                                       In 1986, IBM extended the basic keyboard with the addition of
                                                                       function and control keys. The function keys, arranged in a line
               Your basic Windows keyboard                             across the top of the keyboard, could be assigned specific
At its essence, a keyboard is a series of switches connected to a      commands by the current application or the operating system.
microprocessor that monitors the state of each switch and              Control keys provided cursor and screen control. Four keys
initiates a specific response to a change in that state. In this       arranged in an inverted T formation between the typing keys and
edition of How Stuff Works, you will learn more about this             numeric keypad allow the user to move the cursor on the display
switching action, and about the different types of keyboards,          in small increments. The control keys allow the user to make large
how they connect and talk to your computer, and what the               jumps in most applications. Common control keys include:
components of a keyboard are.                                          * Home * End * Insert * Delete * Page Up * Page Down
                                                                       * Control (Ctrl) * Alternate (Alt) * Escape (Esc)
                                                                       The Windows keyboard adds some extra control keys: two
                                                                       Windows or Start keys, and an Application key.
                                                               Page 72
                  Inside the Keyboard                                  presses the keyswitch against the circuit, there is usually a small
                                                                       amount of vibration between the surfaces, known as bounce. The
The processor in a keyboard has to understand several things           processor in a keyboard recognizes that this very rapid switching
that are important to the utility of the keyboard, such as:            on and off is not caused by you pressing the key repeatedly.
* Position of the key in the key matrix.                               Therefore, it filters all of the tiny fluctuations out of the signal
* The amount of bounce and how to filter it.                           and treats it as a single keypress.
* The speed at which to transmit the typematics.
                                                                       If you continue to hold down a key, the processor determines
                                                                       that you wish to send that character repeatedly to the computer.
                                                                       This is known as typematics. In this process, the delay between
                                                                       each instance of a character can normally be set in software,
                                                                       typically ranging from 30 characters per second (cps) to as few as
                                                                       two cps.
                                                                                        Keyboard Technologies
                                                                       Keyboards use a variety of switch technologies. It is interesting
                                                                       to note that we generally like to have some audible and tactile
                                                                       response to our typing on a keyboard. We want to hear the keys
The microprocessor and controller circuitry of a                       “click” as we type, and we want the keys to feel firm and spring
keyboard.                                                              back quickly as we press them. Let’s take a look at these different
The key matrix is the grid of circuits underneath the keys. In all
                                                                       * Rubber dome mechanical
keyboards except for capacitive ones, each circuit is broken at
                                                                       * Capacitive non-mechanical
the point below a specific key. Pressing the key bridges the gap
                                                                       * Metal contact mechanical
in the circuit, allowing a tiny amount of current to flow through.
                                                                       * Membrane mechanical
The processor monitors the key matrix for signs of continuity at
                                                                       * Foam element mechanical
any point on the grid. When it finds a circuit that is closed, it
compares the location of that circuit on the key matrix to the
character map in its ROM. The character map is basically a
comparison chart for the processor that tells it what the key at x,y
coordinates in the key matrix represents. If more than one key is
pressed at the same time, the processor checks to see if that
combination of keys has a designation in the character map. For
example, pressing the a key by itself would result in a small letter
“a” being sent to the computer. If you press and hold down the
Shift key while pressing the a key, the processor compares that
combination with the character map and produces a capital letter
                                                                              This keyboard uses rubber dome switches.

                 A look at the key matrix.
The character map in the keyboard can be superseded by a
different character map provided by the computer. This is done
quite often in languages whose characters do not have English
equivalents. Also, there are utilities for changing the character
map from the traditional QWERTY to DVORAK or another                   Probably the most popular switch technology in use today is
custom version.                                                        rubber dome. In these keyboards, each key sits over a small,
Keyboards rely on switches that cause a change in the current          flexible rubber dome with a hard carbon center. When the key is
flowing through the circuits in the keyboard. When the key             pressed, a plunger on the bottom of the key pushes down
                                                                Page 73
against the dome. This causes the carbon center to push down            The most common keyboard connectors are:
also, until it presses against a hard flat surface beneath the key      * 5-pin DIN (Deustche Industrie Norm) connector
matrix. As long as the key is held, the carbon center completes         * 6-pin IBM PS/2 mini-DIN connector
the circuit for that portion of the matrix. When the key is released,   * 4-pin USB (Universal Serial Bus) connector
the rubber dome springs back to its original shape, forcing the         * internal connector (for laptops)
key back up to its at-rest position.
                                                                        Normal DIN connectors are rarely used anymore. Most comput-
Rubber dome switch keyboards are inexpensive, have pretty               ers use the mini-DIN PS/2 connector; but an increasing number
good tactile response and are fairly resistant to spills and            of new systems are dropping the PS/2 connectors in favor of
corrosion because of the rubber layer covering the key matrix.          USB. No matter which type of connector is used, two principal
Membrane switches are very similar in operation to rubber dome          elements are sent through the connecting cable. The first is
keyboards. A membrane keyboard does not have separate keys              power for the keyboard. Keyboards require a small amount of
though. Instead, it has a single rubber sheet with bulges for each      power, typically about 5 volts, in order to function. The cable
key. You have seen membrane switches on many devices                    also carries the data from the keyboard to the computer.
designed for heavy industrial use or extreme conditions. Because
                                                                        The other end of the cable connects to a port that is monitored
they offer almost no tactile response and can be somewhat
                                                                        by the computer’s keyboard controller. This is an integrated
difficult to manipulate, these keyboards are seldom found on
                                                                        circuit (IC) whose job is to process all of the data that comes from
normal computer systems.
                                                                        the keyboard and forward it to the operating system. When the
Capacitive switches are considered to be non-mechanical                 operating system is notified that there is data from the keyboard,
because they do not simply complete a circuit like the other            a number of things can happen:
keyboard technologies. Instead, current is constantly flowing           * It checks to see if the keyboard data is a system level com-
through all parts of the key matrix. Each key is spring-loaded, and       mand. A good example of this is Ctrl-Alt-Delete on a Windows
has a tiny plate attached to the bottom of the plunger. When a            computer, which initiates a reboot.
key is pressed, this plate is brought very close to another plate       * The operating system then passes the keyboard data on to the
just below it. As the two plates are brought closer together, it          current application.
affects the amount of current flowing through the matrix at that        * The current application understands the keyboard data as an
point. The processor detects the change and interprets it as a            application-level command. An example of this would be Alt - f,
keypress for that location. Capacitive switch keyboards are               which opens the File menu in a Windows application.
expensive, but do not suffer from corrosion and have a longer life      * The current application is able to accept keyboard data as
than any other keyboard. Also, they do not have problems with             content for the application (anything from typing a document
bounce since the two surfaces never come into actual contact.             to entering a URL to performing a calculation), or
Metal contact and foam element keyboards are not as                     * The current application does not accept keyboard data and
common as they used to be. Metal contact switches simply have             therefore ignores the information.
a spring-loaded key with a strip of metal on the bottom of the          Once the keyboard data is identified as either system-specific or
plunger. When the key is pressed, the metal strip connects the          application-specific, it is processed accordingly. The really
two parts of the circuit. The foam element switch is basically the      amazing thing is how quickly all of this happens. As I type this
same design but with a small piece of spongy foam between the           article, there is no perceptible time lapse between my fingers
bottom of the plunger and the metal strip, providing for a better       pressing the keys and the characters appearing on my monitor.
tactile response. Both technologies have good tactile response,         When you think about everything the computer is doing to make
make satisfyingly audible “clicks” and are inexpensive to               each single character appear, it is simply incredible!
produce. The problem is that the contacts tend to wear out or
corrode faster than on keyboards that use other technologies.
Also, there is no barrier that prevents dust or liquids from coming
                                                                                Good Boot Guide to Your CDs
in direct contact with the circuitry of the key matrix.                               And CD Burner
      From the Keyboard to the Computer
                                                                        CDs and DVDs are everywhere these days. Whether they are
As you type, the processor in the keyboard is analyzing the key         used to hold music, data or computer software, they have
matrix and determining what characters to send to the computer.         become the standard medium for distributing large quantities of
It maintains these characters in a buffer of memory that is usually     information in a reliable package. Compact discs are so easy and
about 16 bytes large. It then sends the data in a stream to the         cheap to produce that America Online sends out millions of them
computer via some type of connection.                                   every year to entice new users. And if you have a computer and
                                                                        CD-R drive, you can create your own CDs, including any
                                      A PS/2 type keyboard
                                                                        information you want.
                                                                        In this Chapter, we will look at how CDs and CD drives work. We
                                                                        will also look at the different forms CDs take, as well as what the
                                                                        future holds for this technology.
                                                                Page 74
                 Understanding the CD
A CD can store up to 74 minutes of music, so the total amount of
digital data that must be stored on a CD is:
44,100 samples/channel/second x 2 bytes/sample x 2 channels
  x 74 minutes x 60 seconds/minute = 783,216,000 bytes

To fit more than 783 megabytes (MB) onto a disc only 4.8 inches
(12 cm) in diameter requires that the individual bytes be very
small. By examining the physical construction of a CD, you can          You will often read about “pits” on a CD instead of bumps. They
begin to understand just how small these bytes are.                     appear as pits on the aluminum side, but on the side the laser
                                                                        reads from, they are bumps.
A CD is a fairly simple piece of plastic, about four one-hun-
dredths (4/100) of an inch (1.2 mm) thick. Most of a CD consists        The incredibly small dimensions of the bumps make the spiral
of an injection-molded piece of clear polycarbonate plastic.            track on a CD extremely long. If you could lift the data track off a
During manufacturing, this plastic is impressed with microscopic        CD and stretch it out into a straight line, it would be 0.5 microns
bumps arranged as a single, continuous, extremely long spiral           wide and almost 3.5 miles (5 km) long!
track of data. We’ll return to the bumps in a moment. Once the          To read something this small you need an incredibly precise disc-
clear piece of polycarbonate is formed, a thin, reflective aluminum     reading mechanism.
layer is sputtered onto the disc, covering the bumps. Then a thin
acrylic layer is sprayed over the aluminum to protect it. The label                                CD Player
is then printed onto the acrylic. A cross section of a complete CD
                                                                        The CD player has the job of finding and reading the data stored
(not to scale) looks like this:
                                                                        as bumps on the CD. Considering how small the bumps are, the
                                                                        CD player is an exceptionally precise piece of equipment. The
                                                                        drive consists of three fundamental components:
                                                                        * A drive motor spins the disc. This drive motor is precisely
                                                                          controlled to rotate between 200 and 500 rpm depending on
                                                                          which track is being read.
                                                                        * A laser and a lens system focus in on and read the bumps.
                                                                        * A tracking mechanism moves the laser assembly so that the
                     Cross-section of a CD                               laser’s beam can follow the spiral track. The tracking system
                                                                          has to be able to move the laser at micron resolutions.

A CD has a single spiral track of data, circling from the inside of
the disc to the outside. The fact that the spiral track starts at the
center means that the CD can be smaller than 4.8 inches (12 cm) if
desired, and in fact there are now plastic baseball cards and
business cards that you can put in a CD player. CD business
cards hold about 2 MB of data before the size and shape of the          Inside the CD player, there is a good bit of computer technology
card cuts off the spiral.                                               involved in forming the data into understandable data blocks and
                                                                        sending them either to the DAC (in the case of an audio CD) or to
What the previous picture will not impress upon you is how              the computer (in the case of a CD-ROM drive).
incredibly small the data track is - it is approximately 0.5 microns
wide, with 1.6 microns separating one track from the next. (A           The fundamental job of the CD player is to focus the laser on the
micron is a millionth of a meter.) And the elongated bumps that         track of bumps. The laser beam passes through the polycarbon-
make up the track are each 0.5 microns wide, a minimum of 0.83          ate layer, reflects off the aluminum layer and hits an opto-
microns long and 125 nanometers high. (A nanometer is a                 electronic device that detects changes in light. The bumps reflect
billionth of a meter.) Looking through the polycarbonate layer at       light differently than the “lands” (the rest of the aluminum layer),
the bumps, they look something like this:                               and the opto-electronic sensor detects that change in reflectivity.
                                                                Page 75
The electronics in the drive interpret the changes in reflectivity in     “where it is” on the disc. This problem is solved using what is
order to read the bits that make up the bytes.                            known as subcode data. Subcode data can encode the
                                                                          absolute and relative position of the laser in the track, and can
                                                                           also encode such things as song titles.
                                                                        * Because the laser may misread a bump, there need to be
                                                                            error-correcting codes to handle single-bit errors. To solve
                                                                          this problem, extra data bits are added that allow the drive to
                                                                          detect single-bit errors and correct them.
                                                                        * Because a scratch or a speck on the CD might cause a whole
The hardest part is keeping the laser beam centered on the data
                                                                          packet of bytes to be misread (known as a burst error), the
track. This centering is the job of the tracking system. The
                                                                          drive needs to be able to recover from such an event. This
tracking system, as it plays the CD, has to continually move the
                                                                          problem is solved by actually interleaving the data on the disc,
laser outward. As the laser moves outward from the center of the
                                                                          so that it is stored non-sequentially around one of the disc’s
disc, the bumps move past the laser faster - this happens
                                                                          circuits. The drive actually reads data one revolution at a time,
because the linear, or tangential, speed of the bumps is equal to
                                                                          and un-interleaves the data in order to play it.
the radius times the speed at which the disc is revolving (rpm).
                                                                        * If a few bytes are misread in music, the worst thing that can
Therefore, as the laser moves outward, the spindle motor must
                                                                          happen is a little fuzz during playback. When data is stored on
slow the speed of the CD. That way, the bumps travel past the
                                                                          a CD, however, any data error is catastrophic. Therefore,
laser at a constant speed, and the data comes off the disc at a
                                                                          additional error correction codes are used when storing data on
constant rate.
                                                                         a CD-ROM.
                                                                                        How CD Burners Work
                                                                        In 2000, one of the biggest news stories was the rise of Napster
                                                                        and similar file-sharing programs. With these programs, you
                                                                        could get an MP3 version of just about any song you want
                                                                        without shelling out a dime. The record companies were fairly
                                                                        upset over this turn of events, and understandably so: They
                                                                        weren’t making any money off the distribution of their product to
                                                                        millions of people.

                       Data Formats
If you have a CD-R drive, and want to produce your own audio
CDs or CD-ROMs, one of the great things you’ve got going in
your favor is the fact that software can handle all the details for
you. You can say to your software, “Please store these songs or
data files on this CD”, and the software will do the rest. Because
of this, you don’t need to know anything about CD data format-
ting to create your own CDs. However, CD data formatting is
complex and interesting, so let’s go into it anyway.
                                                                        An external writable CD drive, also called a CD burner: With
To understand how data are stored on a CD, you need to                  this type of drive, you can take music or data files from your
understand all of the different conditions the designers of the         computer and make your own CDs.
data encoding methodology were trying to handle. Here is a fairly       But there was money to be made on the “Napster revolution,” as
complete list:                                                          electronics manufacturers and retailers soon discovered. In 1999,
* Because the laser is tracking the spiral of data using the bumps,     2000 and early 2001, sales of CD burners and blank CD-Record-
  there cannot be extended gaps where there are no bumps in the         able discs skyrocketed. Suddenly it was feasible for the average
  data track. To solve this problem, data is encoded using EFM          person to gather songs and make their own CDs, and music-mix
  (eight-fourteen modulation). In EFM, 8-bit bytes are converted        makers everywhere wanted to get their hands on the means of
  to 14 bits, and it is guaranteed by EFM that some of those bits       production. Today, writable CD drives (CD burners) are standard
 will be 1s.                                                            equipment in new PCs, and more and more audio enthusiasts are
* Because the laser wants to be able to move between songs,             adding separate CD burners to their stereo systems. In less than
  data needs to be encoded into the music telling the drive             five years, CDs have eclipsed cassette tapes as the mix medium
                                                                        of choice.
                                                               Page 76
                 Reading & Writing CDs
In the last section, we saw that conventional CDs store digital
data as a pattern of bumps and flat areas, arranged in a long
spiral track. The CD fabrication machine uses a high-powered
laser to etch the bump pattern into photoresist material coated
onto a glass plate. Through an elaborate imprinting process, this
pattern is pressed onto acrylic discs. The discs are then coated
with aluminum (or another metal) to create the readable reflec-
tive surface. Finally, the disc is coated with a transparent plastic
layer that protects the reflective metal from nicks, scratches and

                                                                       A CD-R doesn’t have the same bumps and lands as a
       The different layers of a conventional CD                       conventional CD. Instead, the disc has a dye layer
                                                                       underneath a smooth, reflective surface. On a blank CD-R
As you can see, this is a fairly complex, delicate operation,          disc, the dye layer is completely translucent, so all light
involving many steps and several different materials. Like most        reflects. The write laser darkens the spots where the
complex manufacturing processes (from newspaper printing to            bumps would be in a conventional CD, forming non-reflecting
television assembly), conventional CD manufacturing isn’t              areas.
practical for home use. It’s only feasible for manufacturers who
                                                                       A CD burner’s job, of course, is to “burn” the digital pattern onto
produce hundreds, thousands or millions of CD copies.
                                                                       a blank CD. In the next section, we’ll look inside a burner to see
Consequently, conventional CDs have remained a “read only”             how it accomplishes this task.
storage medium for the average consumer, like LPs or conven-
tional DVDs. To audiophiles accustomed to recordable cassettes,
                                                                                               Burning CDs
as well as computer users who were fed up with the limited             In the last section, we saw that CD burners darken microscopic
memory capacity of floppy disks, this limitation seemed like a         areas of CD-R discs to record a digital pattern of reflective and
major drawback of CD technology. In the early ’90s, more and           non-reflective areas that can be read by a standard CD player.
more consumers and professionals were looking for a way to             Since the data must be accurately encoded on such a small scale,
make their own CD-quality digital recordings.                          the burning system must be extremely precise. Still, the basic
In response to this demand, electronics manufacturers intro-           process at work is quite simple.
duced an alternative sort of CD that could be encoded in a few         The CD burner has a moving laser assembly, just like an ordinary
easy steps. CD-recordable discs, or CD-Rs, don’t have any              CD player. But in addition to the standard “read laser,” it has a
bumps or flat areas at all. Instead, they have a smooth reflective     “write laser.” The write laser is more powerful than the read
metal layer, which rests on top of a layer of photosensitive dye.      laser, so it interacts with the disc differently: It alters the
                                                                       surface instead of just bouncing light off it. Read lasers are not
When the disc is blank, the dye is translucent: Light can shine
through and reflect off the metal surface. But when you heat the       intense enough to darken the dye material, so simply playing a
dye layer with concentrated light of a particular frequency and        CD-R in a CD drive will not destroy any encoded information.
intensity, the dye turns opaque: It darkens to the point that light    The write laser moves in exactly the same way as the read laser: It
can’t pass through.                                                    moves outward while the disc spins. The bottom plastic layer has
By selectively darkening particular points along the CD track,         grooves pre-pressed into it, to guide the laser along the correct
and leaving other areas of dye translucent, you can create a           path. By calibrating the rate of spin with the movement of the
digital pattern that a standard CD player can read. The light from     laser assembly, the burner keeps the laser running along the track
the player’s laser beam will only bounce back to the sensor when       at a constant rate of speed. To record the data, the burner simply
the dye is left translucent, in the same way that it will only         turns the laser writer on and off in synch with the pattern of 1s
bounce back from the flat areas of a conventional CD. So, even         and 0s. The laser darkens the material to encode a 0 and leaves it
though the CD-R disc doesn’t have any bumps pressed into it at         translucent to encode a 1.
all, it behaves just like a standard disc.                             Most CD burners can create CDs at multiple speeds. At 1x speed,
                                                                       the CD spins at about the same rate as it does when the player is
                                                                       reading it. This means it would take you about 60 minutes to
                                                            Page 77
                                                                                             Erasing CDs
                                                                    In the last section, we looked at the most prevalent writable CD
                                                                    technology, CD-R. CD-R discs hold a lot of data, work with most
                                                                    CD players and are fairly inexpensive. But unlike tapes, floppy
                                                                    disks and many other data-storage mediums, you cannot re-
                                                                    record on CD-R disc once you’ve filled it up.
                                                                    CD-RW discs have taken the idea of writable CDs a step further,
                                                                    building in an erase function so you can record over old data you
                                                                    don’t need anymore. These discs are based on phase-change
                                                                    technology. In CD-RW discs, the phase-change element is a
                                                                    chemical compound of silver, antimony, tellurium and indium. As
                                                                    with any physical material, you can change this compound’s form
                                                                    by heating it to certain temperatures. When the compound is
                                                                    heated above its melting temperature (around 600 degrees
                                                                    Celsius), it becomes a liquid; at its crystallization temperature
                                                                    (around 200 degrees Celsius), it turns into a solid.
           The laser assembly inside a CD burner

The machinery in a CD burner looks pretty much the same as          In a CD-RW disc, the reflecting lands and non-reflecting
the machinery in any CD player. There is a mechanism that           bumps of a conventional CD are represented by phase shifts in
spins the disc and another mechanism that slides the laser          a special compound. When the compound is in a crystalline
assembly.                                                           state, it is translucent, so light can shine through to the metal
                                                                    layer above and reflect back to the laser assembly. When the
record 60 minutes of music. At 2x speed, it would take you about    compound is melted into an amorphous state, it becomes
half an hour to record 60 minutes, and so on. For faster burning    opaque, making the area non-reflective.
speeds, you need more advanced laser-control systems and a          In phase-change compounds, these shifts in form can be “locked
faster connection between the computer and the burner. You also     into place”: They persist even after the material cools down
need a blank disc that is designed to record information at this    again. If you heat the compound in CD-RW discs to the melting
speed.                                                              temperature and let it cool rapidly, it will remain in a fluid,
The main advantage of CD-R discs is that they work in almost all    amorphous state, even though it is below the crystallization
CD players and CD-ROMS, which are among the most prevalent          temperature. In order to crystallize the compound, you have to
media players today. In addition to this wide compatibility, CD-    keep it at the crystallization temperature for a certain length of
Rs are relatively inexpensive.                                      time so that it turns into a solid before it cools down again.
The main drawback of the format is that you can’t reuse the         In the compound used in CD-RW discs, the crystalline form is
discs. Once you’ve burned in the digital pattern, it can’t be       translucent while the amorphous fluid form will absorb most light.
erased and re-written. In the mid ’90s, electronics manufacturers   On a new, blank CD, all of the material in the writable area is in the
introduced a new CD format that addressed this problem. In the      crystalline form, so light will shine through this layer to the
next section, we’ll look at these CD-rewritable discs, commonly     reflective metal above and bounce back to the light sensor. To
called CD-RWs, to see how they differ from standard CD-R discs.     encode information on the disc, the CD burner uses its write
                                                                    laser, which is powerful enough to heat the compound to its
                                                                  Page 78
melting temperature. These “melted” spots serve the same                   on the disc. The filler data breaks up these large sections.
purpose as the bumps on a conventional CD and the opaque                 * Extra data bits are included to help the player recognize and fix
spots on a CD-R: They block the “read” laser so it won’t reflect           a mistake. If the read laser misreads a single bit, the player is
off the metal layer. Each non-reflective area indicates a 0 in the         able to correct the problem using the additional encoded data.
digital code. Every spot that remains crystalline is still reflective,   * Recorded information is not encoded sequentially; it is
indicating a 1.                                                            interlaced in a set pattern. This reduces the risk of losing whole
                                                                           sections of data. If a scratch or piece of debris makes a part of
As with CD-Rs, the read laser does not have enough power to
                                                                           the track unreadable, it will damage separate bits of data from
change the state of the material in the recording layer — it’s a lot
                                                                           different parts of the song or file, instead of eliminating an
weaker than the write laser. The erase laser falls somewhere in
                                                                           entire segment of information. Since only small pieces of each
between: While it isn’t strong enough to melt the material, it does
                                                                           file segment are unreadable, it’s easier for the CD player to
have the necessary intensity to heat the material to the crystalli-
                                                                           correct the problem or recover from it.
zation point. By holding the material at this temperature, the erase
laser restores the compound to its crystalline state, effectively
erasing the encoded 0. This clears the disc so new data can be                                    Trailer Track
encoded.                                                                  CD-Rs and CD-RWs have a component that ordinary music
CD-RW discs do not reflect as much light as older CD formats, so          CDs do not have - an extra bit of track at the beginning of the
they cannot be read by most older CD players and CD-ROM                   CD, before time zero (00:00), which is the starting point
drives. Some newer drives and players, including all CD-RW                recognized by CD players. This additional track space
writers, can adjust the read laser to work with different CD              includes the power memory area (PMA) and the power
formats. But since CD-RWs will not work on many CD players,               calibration area (PCA). The PMA stores a temporary table of
these are not a good choice for music CDs. For the most part,              contents for the individual packets on a disc that has been
they are used as back-up storage devices for computer files.              only partially recorded. When you complete the disc, the
                                                                          burner uses this information to create the final table of con-
As we’ve seen, the reflective and non-reflective patterns on a CD          tents.
are incredibly small, and they are burned and read very quickly
with a speeding laser beam. In this system, the chances of a data         The PCA is a sort of testing ground for the CD burner. In
error are fairly high. In the next section, we’ll look at some of the     order to ensure that the write laser is set at the right level, the
ways that CD burners compensate for various encoding prob-                burner will make a series of test marks along the PCA section
lems.                                                                     of track. The burner will then read over these marks, checking
                          CD Formats
                                                                          for the intensity of reflection in marked areas as compared to
                                                                          unmarked areas. Based on this information, the burner deter-
In the previous sections, we looked at the basic idea of CD and           mines the optimum laser setting for writing onto the disc.
CD-burner technology. Using precise lasers or metal molds, you
can mark a pattern of more-reflective areas and less-reflective          The actual arrangement of information on music CDs is incredibly
areas that represent a sequence of 1s and 0s. The system is so           complex. And CD-ROMS — compact discs that contain computer
basic that you can encode just about any sort of digital informa-        files rather than song tracks — have even more extensive error-
tion. There is no inherent limitation on what kind of mark pattern       correction systems. This is because an error in a computer file
you put down on the disc.                                                could corrupt an entire program, while a small uncorrected error
                                                                         on a music CD only means a bit of fuzz or a skipping noise. If you
But in order to make the information accessible to another CD
                                                                         are interested in the various ways that data is arranged on
drive (or player), it has to be encoded in an understandable form.
                                                                         different types of CDs, check out this site.
The established form for music CDs, called ISO 9660, was the
foundation for later CD formats. This format was specifically            With some writable CD formats, you have to prepare all of the
designed to minimize the effect of data errors.                          information before you begin burning. This limitation is built into
                                                                         the original format of CDs as well as the physical design of the
This is accomplished by carefully arranging the recorded data
                                                                         disc itself. After all, the long track forms one continuous,
and mixing it with a lot of extra digital information. There are a
                                                                         connected string of 1s and 0s, and it’s difficult to break this up
number of important aspects involved in this system:
                                                                         into separate sections. With newer disc formats, you can record
* The CD track is marked with a sort of timecode, which tells the        files one “packet” at a time, adding the table of contents and
  CD player what part of the disc it is reading at any particular        other unifying structures once you’ve filled up the disc.
  time. Discs are also encoded with a table of contents, located at
  the beginning of the track (the center of the disc), which tells       CD burners are an amazing piece of technology, and the inner
  the player where particular songs (or files) are written onto the      workings are certainly fascinating. But to the typical computer
  disc.                                                                  user, the most compelling aspect of burners is what you can do
* The data track is broken up by extra filler, so there are no long      with them. In the next section, we’ll find out how you can put all
  strings of 1s or 0s. Without frequent shifts from 1 to 0, there        of this technology to work and make your own music mix.
  would be large sections without a changing pattern of
  reflectivity. This could cause the read laser to “lose its place”
                                                               Page 79
                Creating Your Own CDs                                 Keep in mind that you have a limited amount of disc space to
                                                                      work with. CD-Rs have varying capacities, measured in both
While CD-Rs can store all sorts of digital information, the most      megabytes and minutes. These days, most CD-Rs are either 74
widespread application these days is making music-mix CDs with        minutes or 80 minutes long. Before you move on to burning your
a computer. If you’re new to the world of CD burners, this can        CD, you should make sure that your mix isn’t too long for the
seem like a daunting task. But it’s actually very simple, once you    blank disc.
have the right software and know the general procedure.
                                                                      Once the mix is complete and you have saved it, all you need to
If you have already hooked up your CD burner, the first step in       do is insert a blank CD-R disc into the burner and choose the
making a CD is loading the software you need. This music-             “burn” or “write” option in your music-management software. Be
management software serves several functions:                         sure to select “music CD” rather than “data CD,” or you won’t be
* It converts songs to the correct format for burning.                able to play the disc on ordinary CD players. You’ll also need to
* It allows you to arrange the songs for your mix.                    choose the speed at which you want to burn the disc. Typically, a
* It controls the encoding process for writing to the CD.             slower speed reduces the chance of a major error during the
                                                                      writing process.
These days, most burners are packaged with one or more music
programs, but you can also buy programs or download them over         A lot of things can go wrong when you’re burning a CD, so don’t
the Internet. You may need separate media applications to handle      be surprised if some of them don’t come out right. Since CD-Rs
different elements in the process, but there are some good            can not be overwritten, any irreversible mistake means you’ll
programs that handle everything (see below).                          have to junk the whole disc. Among the CD-burning set, this is
                                                                      called “making a coaster,” as that’s pretty much all you can do
             Music Management Programs                                with the damaged CD.
MP3 Decoding: Winamp, Media Jukebox, Easy CD Creator                  If you continually have problems burning CDs, your drive may
 Deluxe, MusicMatch Jukebox, Real Jukebox, Cool Player.               be defective or your music-management program may be faulty.
Playlist Organization: MusicMatch Jukebox, Real Jukebox,              Before you return your burner, try out some other programs and
 Cool Player, Dj MP3 Media, PCDJ, Collectorz.com MP3                  see if they yield better results.
                                                                      To make a CD-ROM, you’ll go through a similar process - but
CD Ripping: Nero Burning ROM, MusicMatch Jukebox, Easy
                                                                      you’ll code the disc as a data CD, not a music CD. Some newer
 CD Creator Deluxe, Audiograbber
                                                                      CD players and DVD players can read untranslated MP3 data
CD Burning: Nero Burning ROM, Roxio Easy CD Creator 5/6
                                                                      files, and you may be able to make CD-ROM music mixes this
 Platinum, Toast 5 Titanium, Gear Pro 5.02,
                                                                      way. Since MP3s are compressed files, you can fit a lot more of
Multi-Function Software: MusicMatch Jukebox , Winamp,
                                                                      them on a single disc, which means you can make a longer mix.
 Real Jukebox , Media Jukebox
                                                                      The drawback, of course, is that your disc won’t work in the vast
When you have all of the software you need, it’s time to gather       majority of CD players.
some songs. You may want to take songs directly from your CD
                                                                      CD burners have opened up a whole new world to the average
collection. To do this, you need to “rip” the songs - copy them
                                                                      computer user. You can record music that will run in most
from your CD to your computer’s hard drive. You’ll need an
                                                                      anybody’s CD player, or you can put together CD-ROMs
extraction program to do this. To copy a particular track, insert
                                                                      containing photos, Web pages or movies. With a piece of
the CD into your built-in CD-ROM drive (or the CD-burner itself)
                                                                      equipment about the size of a car stereo, and about the price of a
and select the song you want through the extraction program.
                                                                      cheap bicycle, you can set up your own multimedia production
Essentially, the program will play the song and re-record it into a
usable data format. It’s legal to make copies of songs you own,
as long as the CD is only for your personal use.
                                                                             Good Boot Guide to Your DVD
You can also gather MP3s over the Internet. You can download
MP3s from sites like MP3.com or with file-sharing programs like       Nearly every movie produced today is available on DVD,
Gnutella. Some MP3s are free, and can be legally downloaded           and many older movies are being moved to the DVD
and copied onto a CD. Most are illegal copies, however, and it is     format. Often, a movie comes out on DVD before it comes
a copyright violation to download and burn them onto a CD.            out on video tape, because the manufacturing and distribu-
                                                                      tion costs for DVDs are so much lower!
MP3s are compressed files, and you must expand (decode) them
in order to burn them onto a CD. Standard music-management            By bringing outstanding picture and sound to our favorite
programs can decode these files. If you don’t have the right          films, the DVD format is doing for movies exactly what
software, there are a number of decoding programs that you can        CDs did for music.
download over the Internet.                                           In this Chapter article, you will learn what a DVD consists
                                                                      of, how a DVD player reads a disc (a DVD is remarkably
                          MP3 Sites                                   similar to a CD — it has just been designed to hold more
Once you’ve gathered the songs, you can use your music                data), what to look for when buying a DVD player, a little
manager to arrange them in the order you want.                        DVD history and much more!
                                                               Page 80
                          The Basics
                                                                       are made, each one is coated with lacquer, squeezed together and
DVD Fact: The first DVD player hit the market in March 1997.           cured under infrared light. For single-sided discs, the label is silk-
A DVD is very similar to a CD, but it has a much larger data           screened onto the nonreadable side. Double-sided discs are
capacity. A standard DVD holds about seven times more data             printed only on the nonreadable area near the hole in the middle.
than a CD does. This huge capacity means that a DVD has                Cross sections of the various types of completed DVDs (not to
enough room to store a full-length, MPEG-2-encoded movie, as           scale) look like this:
well as a lot of other information.
Here are the typical contents of a DVD movie:
* Up to 133 minutes of high-resolution video, in letterbox or
  pan-and-scan format, with 720 dots of horizontal resolution
 (The video compression ratio is typically 40:1 using MPEG-2
* Soundtrack presented in up to eight languages using 5.1
  channel Dolby digital surround sound
* Subtitles in up to 32 languages
DVD can also be used to store almost eight hours of CD-quality
music per side.
                     DVD Advantages
* DVD picture quality is better, and many of DVDs have Dolby
  Digital or DTS sound, which is much closer to the sound you
 experience in a movie theater.
* Many DVD movies have an on-screen index, where the creator
  of the DVD has labeled many of the significant parts of the
  movie, sometimes with a picture. With your remote, if you
  select the part of the movie you want to view, the DVD player
  will take you right to that part, with no need to rewind or fast-                           It’s Truly Tiny
  forward.                                                             Each writable layer of a DVD has a spiral track of data. On single-
* DVD players are compatible with audio CDs.                           layer DVDs, the track always circles from the inside of the disc to
* Some DVD movies have both the letterbox format, which fits           the outside. That the spiral track starts at the center means that a
  wide-screen TVs, and the standard TV size format, so you can         single-layer DVD can be smaller than 12 centimeters if desired.
  choose which way you want to watch the movie.
* DVD movies may have several soundtracks on them, and they
  may provide subtitles in different languages. Foreign movies
   may give you the choice between the version dubbed into your
  language, or the original soundtrack with subtitles in your

                Storing Data on a DVD
DVDs are of the same diameter and thickness as CDs, and they
are made using some of the same materials and manufacturing
methods. Like a CD, the data on a DVD is encoded in the form of
small pits and bumps in the track of the disc.
A DVD is composed of several layers of plastic, totaling about
1.2 millimeters thick. Each layer is created by injection molding
polycarbonate plastic. This process forms a disc that has
microscopic bumps arranged as a single, continuous and                 What the image to the right cannot impress upon you is how
extremely long spiral track of data. More on the bumps later.          incredibly tiny the data track is - just 740 nanometers separate
Once the clear pieces of polycarbonate are formed, a thin              one track from the next (a nanometer is a billionth of a meter).
reflective layer is sputtered onto the disc, covering the bumps.       And the elongated bumps that make up the track are each 320
Aluminum is used behind the inner layers, but a semi-reflective        nanometers wide, a minimum of 400 nanometers long and 120
gold layer is used for the outer layers, allowing the laser to focus   nanometers high. The following figure illustrates looking through
through the outer and onto the inner layers. After all of the layers   the polycarbonate layer at the bumps.
                                                              Page 81
                                                                      repetition of information that is already on the disc. The error
                                                                      correction scheme that a CD uses is quite old and inefficient
                                                                      compared to the method used on DVDs. The DVD format doesn’t
                                                                      waste as much space on error correction, enabling it to store
                                                                      much more real information. Another way that DVDs achieve
                                                                      higher capacity is by encoding data onto a slightly larger area of
                                                                      the disc than is done on a CD.
                                                                                        Multi-Layer Storage
                                                                      To increase the storage capacity even more, a DVD can have up
                                                                      to four layers, two on each side. The laser that reads the disc can
                                                                      actually focus on the second layer through the first layer. Here is
                                                                      a list of the capacities of different forms of DVDs:

You will often read about “pits” on a DVD instead of bumps.
They appear as pits on the aluminum side, but on the side that
the laser reads from, they are bumps.
The microscopic dimensions of the bumps make the spiral track
on a DVD extremely long. If you could lift the data track off a       You may be wondering why the capacity of a DVD doesn’t
single layer of a DVD, and stretch it out into a straight line, it    double when you add a whole second layer to the disc. This is
would be almost 7.5 miles long! That means that a double-sided,       because when a disc is made with two layers, the pits have to be
double-layer DVD would have 30 miles (48 km) of data!                 a little longer, on both layers, than when a single layer is used.
                                                                      This helps to avoid interference between the layers, which would
To read bumps this small you need an incredibly precise disc-         cause errors when the disc is played.
reading mechanism.
                                                                                      The DVD Video Format
             Data Storage: DVD vs. CD
                                                                      DVD Fact: If an average DVD movie were uncompressed, it
DVDs can store more data than CDs for a few reasons:                  would take at least a year to download it over a normal phone
* Higher-density data storage                                         line.
* Less overhead, more area
* Multi-layer storage                                                 Even though its storage capacity is huge, the uncompressed
                                                                      video data of a full-length movie would never fit on a DVD.
             Higher Density Data Storage
                                                                      In order to fit a movie on a DVD, you need video compression. A
Single-sided, single-layer DVDs can store about seven times
                                                                      group called the Moving Picture Experts Group (MPEG) estab-
more data than CDs. A large part of this increase comes from the
                                                                      lishes the standards for compressing moving pictures.
pits and tracks being smaller on DVDs.
                                                                      When movies are put onto DVDs, they are encoded in MPEG-2
                                                                      format and then stored on the disc. This compression format is a
                                                                      widely accepted international standard. Your DVD player
                                                                      contains an MPEG-2 decoder, which can uncompress this data as
                                                                      quickly as you can watch it.
                                                                       The MPEG-2 Format and Data Size Reduction
                                                                      A movie is usually filmed at a rate of 24 frames per second. This
Let’s try to get an idea of how much more data can be stored due
                                                                      means that every second, there are 24 complete images displayed
to the physically tighter spacing of pits on a DVD. The track
                                                                      on the movie screen. American and Japanese television use a
pitch on a DVD is 2.16 times smaller, and the minimum pit length
                                                                      format called NTSC, which displays a total of 30 frames per
for a single-layer DVD is 2.08 times smaller than on a CD. By
                                                                      second; but it does this in a sequence of 60 fields, each of which
multiplying these two numbers, we find that there is room for
                                                                      contains alternating lines of the picture. Other countries use PAL
about 4.5 times as many pits on a DVD. So where does the rest of
                                                                      format, which displays at 50 fields per second, but at a higher
the increase come from?
                                                                      resolution (see How Video Formatting Works for details on these
              Less Overhead, More Area                                formats). Because of the differences in frame rate and resolution,
                                                                      an MPEG movie needs to be formatted for either the NTSC or the
On a CD, there is a lot of extra information encoded on the disc to
                                                                      PAL system.
allow for error correction — this information is really just a
                                                                Page 82
                         Frame This!                                    can hold 74 minutes of music at their highest quality level,
                                                                        192kHz/24-bit audio. By lowering either the sampling rate or the
The MPEG encoder that creates the compressed movie file                 accuracy, DVDs can be made to hold more music. A DVD audio
analyzes each frame and decides how to encode it. The compres-          disc can store up to two hours of 6-channel, better than CD
sion uses some of the same technology as still image compres-           quality, 96kHz/24-bit music. Lower the specifications further, and
sion does to eliminate redundant or irrelevant data. It also uses       a DVD audio disc can hold almost seven hours of CD-quality
information from other frames to reduce the overall size of the file.   audio.
Each frame can be encoded in one of three ways:
* As an intraframe - An intraframe contains the complete
  image data for that frame. This method of encoding provides
  the least compression.
* As a predicted frame - A predicted frame contains just
  enough information to tell the DVD player how to display the
  frame based on the most recently displayed intraframe or
  predicted frame. This means that the frame contains only the
  data that relates to how the picture has changed from the
  previous frame.
* As a bidirectional frame - In order to display this type of           In an audio CD or DVD, each bit represents a digital command
  frame, the player must have the information from the surround         telling the DAC what voltage level to output (see How Analog
  ing intraframe or predicted frames. Using data from the closest       and Digital Recording Works for details). While an ideal record-
  surrounding frames, it uses interpolation (something like             ing would follow the raw waveform exactly, digital recordings
  averaging) to calculate the position and color of each pixel.         sample the sound at different frequencies, and therefore lose
Did you know? DVDs often have special features hidden on the            some of the data.
disc. These “Easter eggs” can be previews of other movies,
computer software or music. DVD Review has a listing of some
great Easter eggs that viewers have found on DVDs.
Depending on the type of scene being converted, the encoder
will decide which types of frames to use. If a newscast were
being converted, a lot more predicted frames could be used,
because most of the scene is unaltered from one frame to the
next. On the other hand, if a very fast action scene were being
converted, in which things changed very quickly from one frame
to the next, more intraframes would have to be encoded. The
newscast would compress to a much smaller size than the action
If all of this sounds complicated, then you are starting to get a       The previous figure is a comparison of a raw audio signal to the
feeling for how much work your DVD player does to decode an             CD audio and DVD audio output.
MPEG-2 movie. A lot of processing power is required; even some
computers with DVD players can’t keep up with the processing            The graph above shows how the highest quality DVD audio
required to play a DVD movie.                                           compares to CD audio. You can see that DVD follows the signal
                                                                        more closely, but it’s still a long way from perfect.
                          DVD Audio
                                                                                                Sound Check
DVD audio and DVD video are different formats. DVD audio
discs and players are relatively rare right now, but they will          To get the full experience of the Dolby Digital sound used on
become more common, and the difference in sound quality                 many DVDs, you need a home theater system with five speakers,
should be noticeable. In order to take advantage of higher-             a subwoofer, and a receiver that is either “Dolby Digital ready” or
quality DVD audio discs, you will need a DVD player with a              has a built-in Dolby Digital decoder.
192kHz/24-bit digital-to-analog converter (DAC). Most DVD               If your receiver is Dolby Digital ready, then it does not have a
players have only a 96kHz/24-bit digital-to-analog converter. So if     Dolby Digital decoder, so you need to buy a DVD player with its
you want to be able to listen to DVD audio discs, be sure to look       own Dolby Digital decoder and 5.1 channel outputs. If you also
for a DVD audio player with a 192kHz/24-bit digital-to-analog           want your system to be compatible with DTS sound, then your
converter.                                                              DVD player will need a DTS decoder, too.
DVD audio recordings can provide far better sound quality than          Did you know? Some DVDs carry commentary tracks, in which
CDs. The chart below lists the sampling rate and accuracy for CD        the filmmaker talks about the movie while it is running. This can
recordings and the maximum sampling rate and accuracy for DVD           be very exciting for true film buffs. DVDs can also contain extra,
recordings. CDs can hold 74 minutes of music. DVD audio discs           previously unreleased scenes. And a DVD is sometimes a
                                                                 Page 83
director’s cut - the film as the director originally intended it. If   The hardest part of reading a DVD is keeping the laser beam
your receiver has its own Dolby Digital decoder and DTS                centered on the data track. This centering is the job of the
decoder, then you don’t need a DVD player with 5.1 channel             tracking system. As the DVD is played, the tracking system has
outputs, and you can save some money on cables by using the            to move the laser continually outward. As the laser moves
digital outputs.                                                       outward from the center of the disc, the bumps move past the
                      The DVD Player                                   laser at an increasing speed. This happens because the linear, or
                                                                       tangential, speed of the bumps is equal to the radius times the
DVD Fact: The Sony PlayStation 2 was the first video game              speed at which the disc is revolving. So, as the laser moves
system able to play DVDs.                                              outward, the spindle motor must slow the spinning of the DVD
A DVD player is very similar to a CD player. It has a laser            so that the bumps travel past the laser at a constant speed, and
assembly that shines the laser beam onto the surface of the disc       the data comes off the disc at a constant rate.
to read the pattern of bumps (see How CDs Work for details).
The DVD player decodes the MPEG-2 encoded movie, turning it
into a standard composite video signal. The player also decodes
the audio stream and sends it to a Dolby decoder, where it is
amplified and sent to the speakers.
                   Inside a DVD Drive
The DVD player has the job of finding and reading the data
stored as bumps on the DVD. Considering how small the bumps
are, the DVD player has to be an exceptionally precise piece of
equipment. The drive consists of three fundamental components:
* A drive motor to spin the disc - The drive motor is precisely
  controlled to rotate between 200 and 500 rpm, depending on
  which track is being read.                                           An interesting thing to note is that if a DVD has a second layer,
* A laser and a lens system to focus in on the bumps and read          the start of that layer’s data track can be at the outside of the disc
  them - The light from this laser has a smaller wavelength (640       instead of the inside. This allows the player to transition quickly
  nanometers) than the light from the laser in a CD player (780        from one layer to the next, without a delay in data output,
  nanometers), which allows the DVD laser to focus on the              because it doesn’t have to move the laser back to the center of
  smaller DVD pits.                                                    the disc to read the next layer.
* A tracking mechanism that can move the laser assembly so the
  laser beam can follow the spiral track - The tracking system has                                 Features
  to be able to move the laser at micron resolutions.
                                                                                            Supported Formats
                       Reading a DVD                                   DVD movies Just about all players play DVD movies.
Inside the DVD player, there is a good bit of computer technol-        Music CDs Most players also play music CDs.
ogy involved in forming the data into understandable data              Video CDs Some players can handle this format, which is used
blocks, and sending them either to the DAC, in the case of audio        mostly for music videos and some movies from foreign
or video data, or directly to another component in digital format,      countries.
in the case of digital video or data.                                  CD-Rs Some players can play content that you create on your
                                                                        own computer.
The fundamental job of the DVD player is to focus the laser on         Audio DVDs A few players can handle this format for high-
the track of bumps. The laser can focus either on the semi-             quality audio.
transparent reflective material behind the closest layer, or, in the
case of a double-layer disc, through this layer and onto the                                  Other Features
reflective material behind the inner layer. The laser beam passes
                                                                       Dolby Digital decoder This feature allows the DVD player to
through the polycarbonate layer, bounces off the reflective layer
                                                                        decode the Dolby Digital information from a DVD and convert
behind it and hits an opto-electronic device, which detects
                                                                        it to six separate analog channels. This feature is not necessary
changes in light. The bumps reflect light differently than the
                                                                        if you have a Dolby Digital receiver, which has a digital input
“lands,” the flat areas of the disc, and the opto-electronic sensor
                                                                        that carries all of the audio information.
detects that change in reflectivity. The electronics in the drive
                                                                       DTS decoder This feature allows the DVD player to decode the
interpret the changes in reflectivity in order to read the bits that
                                                                        DTS information from a DVD and convert it to six separate
make up the bytes.
                                                                         analog channels. Again, this feature is not necessary if you
                                                                        have a receiver with a DTS decoder.
                                                                       DTS compatible All DVD players are DTS compatible. They
                                                                        pass the digital audio information on to the receiver, which
                                                                         then decodes it.
                                                              Page 84
Simulated surround If you are going to hook the DVD player
 up to a TV or a stereo system with only two speakers, a DVD
 player with simulated surround processing will give you some
  sense of surround sound without the extra speakers.
Disc capacity Some DVD players can hold three, five or even
 several hundred discs. Since most DVD players can also play
 audio CDs, if you buy a player with a high disc capacity you
 could store your whole CD collection in the machine.
96kHz/24-bit DAC This is the speed and accuracy of the
 digital-to-analog converter (DAC), which converts the audio
 information into an analog signal. Most movie soundtracks are
 encoded in this format, so this is really a required feature, and
 most DVD players will have at least a 96kHz/24-bit DAC.              DVD player video outputs from left to right: compos-
192kHz/24-bit DAC This is an upcoming format for audio-               ite video, s-video, component video
 only DVDs that are recorded at speeds of up to 192kHz and
 24-bits. Only the newest DVD audio players have the 192kHz/
                                                                                             Audio Outputs
 24-bit DAC required to play these audio discs.
Remote-control type DVD players may come with three types
 of remotes:
 * A dedicated remote, which only runs the DVD player
 * A multibrand remote, which can control other components,
  like VCRs and TVs made by other manufacturers (Usually,
    they only support the more common brands.)
 * A learning remote, which can learn the signals from other
    remotes and assign them to a button (This feature is useful if
   you have uncommon brands of components to control.)
                                                                          Coaxial digital output and optical digital output
                         DVD Extras
                                                                      These outputs provide the highest-quality audio. They send the
Because DVDs are so durable, film aficionados can watch a
                                                                      digital sound information to the receiver for decoding. You can
favorite movie repeatedly without the disc losing its quality. This
                                                                      use either one of these if you have a Dolby Digital receiver.
is also good for parents whose children like to watch the same
movies over and over again.                                                               5.1 channel outputs
DVD players allow you to find scenes, play them in slow motion        5.1 channel is a set of six analog outputs, one for each of the
or freeze a scene, and the video quality will remain the same.        Dolby Digital channels (left front, center front, right front, left
                                                                      rear, right rear and subwoofer). The DVD player decodes the
Software loaded from DVD, as opposed to CD-ROM, can contain
                                                                      Dolby Digital signal and uses its own DAC to output an analog
more information. An entire encyclopedia can fit onto one DVD,
                                                                      signal. These are the outputs you’ll need to use if you are
whereas other formats would require multiple discs.                   hooking the DVD player up to a “Dolby Digital ready” receiver.
                       Video Outputs                                  DVD players with 5.1 channel outputs will always have Dolby
                Component-video outputs                               Digital decoders, and they may or may not have DTS decoders. If
                                                                      you have a “Dolby Digital ready” receiver and you want DTS
These outputs provide the highest quality video signal to your        sound, you will need a DVD player with a built-in DTS decoder.
TV. They are quite rare right now; only the newest high-end TVs
can support them. But, if you have such a TV, you’ll definitely                              Stereo outputs
want a DVD player with component video outputs.                       These outputs carry only the stereo music signal. You would use
There are three separate connectors for component video output.       these if you were hooking your DVD player up to a TV that has
The player pictured below has one component video output.             only two speakers.
                      S-video outputs                                              Connecting the DVD Player
TVs with this type of connection are more common. S-video             Connecting a DVD player to your stereo receiver (or television, if
provides a very good picture quality, and every DVD player has        you don’t have a receiver) involves making two basic connec-
at least one of these outputs. The player pictured above has two      tions: audio and video.
of them.                                                                                            Audio
                Composite-video outputs                               The first connection to make is for the audio portion of the
These are the most common type of output, and they provide            signal. There will be several options depending on the receiver
adequate picture quality. Usually, they have a yellow plastic         you have.
insert. The player pictured above has two of these outputs.
                                                               Page 85
* The best choice (if available) is either to use an optical (also                                   FAQ
 called Tos-link) or coaxial (RCA) digital connection. These
  two choices are equal in quality. In order to use either of these,   * What does “DVD” stand for? “DVD” stands for digital
  you will need to have both an output on the DVD player, and            versatile disc, but some sources declare that it doesn’t stand
  an input on the receiver. Only receivers with built-in Dolby           for anything anymore.
                                                                       * Can I record television shows or movies on a DVD
  Digital decoders will have this type of input.
                                                                        player? Yes, you can - if your DVD player is also a DVD
* If your receiver does not have a built-in Dolby Digital or DTS
  decoder, but is “Dolby Digital ready,” look for the 5.1-channel
                                                                       * Can I play CDs on a DVD player? Yes. DVD players are
  Dolby or 5.1-channel DTS. This connection involves six
                                                                        completely compatible with audio compact discs. And music
  cables, corresponding to different speaker channels: left front,
                                                                        will become increasingly available in DVD format. See What
  center front, right front, left rear, right rear and subwoofer.
                                                                        is the difference between DVD-audio and CDs? for more
* The last option to connect the two components is with analog
                                                                        discussion of the DVD audio format.
  RCA outputs. This is a two-cable connection, with one cable
                                                                       * What are region codes? Movie studios use region codes on
  delivering the left speaker sound, and the other cable deliver
                                                                         DVDs to thwart unauthorized copying, and to control the
  ing the right. This connection will deliver only stereo sound,
                                                                         release dates of DVD movies. The actual region code is stored
  but it may be your only option if you are hooking up directly to
                                                                        in one byte on the DVD. The DVD player or drive has a region
  a television, or if you have an old receiver with only two
                                                                        code in its firmware. Personal computer DVD-ROM players
                                                                        often have the code in the software or in the MPEG-2 decoder.
Now let’s take a look at the video connection.
                                                                        For the player or drive to play the movie, the two codes must
                              Video                                     match. The code is also printed on the back of a DVD package,
                                                                        superimposed on a small image of the globe. If you have a
As we mentioned earlier, connecting a DVD player to your stereo
                                                                        DVD that was made for release in Asia, you won’t be able to
receiver (or television, if you don’t have a receiver) involves
                                                                        play it on a DVD player intended for use in Australia.
making two basic connections: audio and video. The second

                                                                                    Good Boot guide to Your
connection is for the video portion of the DVD player.

                                                                                         Blu-ray Discs
* The best quality choice is to use component connection. This
  connection consists of three cables: color-labeled red, blue and
  green. The quality is superb. However, these connections only
  exist on extremely high-end receivers and television sets.
* The next option is s-video. One cable connects the DVD player
  to the receiver in this setup.
* The last option, similar to the audio setup, is to use the analog
  RCA video output, usually color-labeled yellow on both ends.
 This will deliver the lowest quality, but will suffice for most
  older, analog televisions.
                 DVDs and Laser Discs                                  In 1997, a new technology emerged that brought digital sound
                                                                       and video into homes all over the world. It was called DVD, and it
Laser disc is an older technology. It offered a better picture and     revolutionized the movie industry.
better sound than videotapes, and it is comparable to DVD. But
the laser disc format is analog; DVDs are digital (see How Analog      The industry is set for yet another revolution with the introduc-
and Digital Recording Works). Laser discs are only used for            tion of Blu-ray Discs (BD). With their high storage capacity, Blu-
prerecorded movies, and they are larger, about 12 inches in            ray discs can hold and playback large quantities of high-
diameter, instead the 5-inch diameter of DVDs. The two formats         definition video and audio, as well as photos, data and other
usually can’t be played on the same machine.                           digital content.
Laser discs, like DVDs, allow viewers to go to the exact scene         In this Chapter I’ll explain how the Blu-ray disc works and how it
they wish to see, and to freeze a frame or slow the picture. Laser     was developed, and we’ll see how it stacks up against some
discs can only hold an hour on each side, so you have to flip the      other new digital video formats on the horizon.
disc to watch the second half of the movie.                                                      The Name
Because of DVD compression techniques, DVDs can hold more
                                                                       The Blu-ray name is a combination of “blue,” for the
data. You rarely have to flip a DVD to watch a whole movie. Laser
                                                                       color of the laser that is used, and “ray,” for
disc players are noisier than DVD players, and they can some-
                                                                       optical ray. The “e” in “blue” was purposefully left
times suffer “laser rot” — the aluminum side of the disc oxidizes,
                                                                       off, according to the manufacturers, because an
and the quality of the disc deteriorates. DVDs are less likely to
                                                                       everyday word cannot be trademarked.
have this problem, because manufacturing techniques have
improved. As the popularity of DVD grows, laser discs are
becoming harder to find.
                                                               Page 86
               What is a Blu-ray Disc?
A current, single-sided, standard DVD can hold 4.7 GB
(gigabytes) of information. That’s about the size of an average
two-hour, standard-definition movie with a few extra features. But
a high-definition movie, which has a much clearer image (see
How Digital Television Works), takes up about five times more
bandwidth and therefore requires a disc with about five times
more storage. As TV sets and movie studios make the move to
high definition, consumers are going to need playback systems
with a lot more storage capacity.

                                                                                     How Does Blu-ray Work?
                  BD-ROM disc researcher
                                                                       Discs store digitally encoded video and audio information in pits
Blu-ray is the next-generation digital video disc. It can record,      - spiral grooves that run from the center of the disc to its edges.
store and play back high-definition video and digital audio, as        A laser reads the other side of these pits — the bumps — to play
well as computer data. The advantage to Blu-ray is the sheer           the movie or program that is stored on the DVD. The more data
amount of information it can hold:                                     that is contained on a disc, the smaller and more closely packed
* A single-layer Blu-ray disc, which is roughly the same size          the pits must be. The smaller the pits (and therefore the bumps),
   as a DVD, can hold up to 27 GB of data - that’s more than           the more precise the reading laser must be.
   two hours of high-definition video or about 13 hours of
   standard video.                                                     Unlike current DVDs, which use a red laser to read and write data,
* A double-layer Blu-ray disc can store up to 54 GB, enough            Blu-ray uses a blue laser (which is where the format gets its
  to hold about 4.5 hours of high-definition video or more than        name). A blue laser has a shorter wavelength (405 nanometers)
   20 hours of standard video. And there are even plans in the         than a red laser (650 nanometers). The smaller beam focuses more
   works to develop a disc with twice that amount of storage.          precisely, enabling it to read information recorded in pits that are
                                                                       only 0.15 microns (1 micron = 10-6 meters) long - this is more than
Blu-ray discs not only have more storage capacity than tradi-          twice as small as the pits on a DVD. Plus, Blu-ray has reduced the
tional DVDs, but they also offer a new level of interactivity. Users   track pitch from 0.74 microns to 0.32 microns. The smaller pits,
will be able to connect to the Internet and instantly download         smaller beam and shorter track pitch together enable a single-
subtitles and other interactive movie features.                        layer Blu-ray disc to hold more than 25 GB of information —
                                                                       about five times the amount of information that can be stored on
                    Blu-ray Advantages                                 a DVD.
* r ecord high-definition television (HDTV) without any quality        Each Blu-ray disc is about the same thickness (1.2 millimeters) as
  loss                                                                 a DVD. But the two types of discs store data differently. In a
* instantly skip to any spot on the disc                               DVD, the data is sandwiched between two polycarbonate layers,
* record one program while watching another on the disc                each 0.6-mm thick. Having a polycarbonate layer on top of the
* create playlists                                                     data can cause a problem called birefringence, in which the
* edit or reorder programs recorded on the disc                        substrate layer refracts the laser light into two separate beams. If
* automatically search for an empty space on the disc to avoid         the beam is split too widely, the disc cannot be read. Also, if the
  recording over a program                                             DVD surface is not exactly flat, and is therefore not exactly
* access the Web to download subtitles and other extra features        perpendicular to the beam, it can lead to a problem known as disc
                                                                       tilt, in which the laser beam is distorted. All of these issues lead
                                                                       to a very involved manufacturing process.
                                                                Page 87
                                                                       1. The two discs are molded.
                                                                       2. The recording layer is added to one of the discs.
                                                                       3. The two discs are glued together.
                                                                       Blu-ray discs only do the injection-molding process on a single
                                                                       1.1-mm disc, which reduces cost. That savings balances out the
                                                                       cost of adding the protective layer, so the end price is no more
                                                                       than the price of a regular DVD.
                                                                       Blu-ray has a higher data transfer rate - 36 Mbps (megabits per
                                                                       second) - than today’s DVDs, which transfer at 10 Mbps. A Blu-
                                                                       ray disc can record 25 GB of material in just over an hour and a
                                                                            Blu-ray vs. Other New Disc Formats
                                                                       Will Blu-ray replace previous DVDs? Its manufacturers hope so.
                                                                       In the meantime, JVC has developed a Blu-ray/DVD combo disc
                                                                       with an approximate 33.5-GB capacity, allowing for the release of
                     Building a Blu-ray                                video in both formats on a single disc. But Blu-ray is not alone in
The Blu-ray disc overcomes DVD-reading issues by placing the           the marketplace. A few other formats are competing for a share of
data on top of a 1.1-mm-thick polycarbonate layer. Having the          the DVD market.
data on top prevents birefringence and therefore prevents                                         HD-DVD
readability problems. And, with the recording layer sitting closer
to the objective lens of the reading mechanism, the problem of         The other big player is HD-DVD, also called AOD (Advanced
disc tilt is virtually eliminated. Because the data is closer to the   Optical Disc), which was developed by electronics giants
surface, a hard coating is placed on the outside of the disc to        Toshiba and NEC. HD-DVD was actually in the works before
protect it from scratches and fingerprints.                            regular DVD, but it didn’t begin real development until 2003.

Note: Blu-ray discs are better armed than current DVDs. They           The advantage to HD-DVD is that it uses the same basic format
come equipped with a secure encryption system - a unique ID            as the traditional DVD and can therefore be manufactured with
that protects against video piracy and copyright infringement.         the same equipment, saving on costs. The disadvantage is that it
                                                                       can’t match the storage capacity of Blu-ray. A rewritable, single-
                                                                       layer HD-DVD can hold 20 GB of data; a double-layer disc can
                                                                       hold 30 GB (that’s compared to 27 GB and 50 GB for Blu-ray). The
                                                                       read-only versions hold slightly less data. Also, HD-DVD
                                                                       doesn’t offer the interactive capabilities of Blu-ray, although it
                                                                       will probably be less expensive than its competitor.
                                                                                          Other Competitors
                                                                       Blu-ray and HD-DVD are the two major competitors in the market,
                                                                       but there are other contenders, as well. Warner Bros. Pictures has
                                                                       developed its own system, called HD-DVD-9. This system uses a
                                                                       higher compression rate to put more information (about two
                                                                       hours of high-definition video) on a standard DVD. Taiwan has
                                                                       created the Forward Versatile Disc (FVD), an upgraded version of
                                                                       today’s DVDs that allows for more data storage capacity (5.4 GB
                                                                       on a single-sided disc and 9.8 GB on a double-sided disc). And
                                                                       China has introduced the Enhanced Video Disc (EVD), another
                                                                       high-definition video disc.
                                                                       There are also professional versions of the blue laser technology.
                                                                       Sony has developed XDCAM and ProData (Professional Disc for
                                                                       Data). The former is designed for use by broadcasters and AV
                                                                       studios. The latter is primarily for commercial data storage (for
                                                                       example, backing up servers).
The design of the Blu-ray discs saves on manufacturing costs.
Traditional DVDs are built by injection molding the two 0.6-mm
discs between which the recording layer is sandwiched. The
process must be done very carefully to prevent birefringence.
                                                              Page 88
     When Will Blu-ray Become Available?
                                                                         Good Boot Guide to Your Modem,
Blu-ray recorders are already available in Japan, where more
consumers have access to HDTV than in the United States.
                                                                                 Cable and DSL
Outside of Japan, once more TV sets come equipped with a high-
definition tuner and more films and television shows are pro-        In this Chapter, I’ll show you how a modem brings you Web
                                                                     pages. We’ll start with the original 300-baud modems and
                                                                     progress all the way through Cable and DSL.
                                                                     Let’s get started with a short recap of how the modem came to be.
                                                                                       The Origin of Modems

duced in high-definition (which is expected to happen by late
2005 or 2006), Blu-ray movies and TV shows on disc should
become widely available. But the format is already available for     The word “modem” is a contraction of the words modulator-
home recording, professional recording and data storage.             demodulator. A modem is typically used to send digital data over
                                                                     a phone line.
              Sony Blu-ray disc player/recorder
                                                                     The sending modem modulates the data into a signal that is
Another important factor is cost. Just as with most new technolo-    compatible with the phone line, and the receiving modem demodu-
gies, Blu-ray equipment will be pricey at first. In 2003, Sony       lates the signal back into digital data. Wireless modems convert
released its first Blu-ray recorder in Japan with a price tag of     digital data into radio signals and back.
around $3,000. The price is expected to drop as the format gains
popularity. Blu-ray discs may also be initially more expensive       Modems came into existence in the 1960s as a way to allow
than today’s DVDs, but once demand grows and they can be             terminals to connect to computers over the phone lines. A typical
mass-produced, manufacturers say the price will drop to within       arrangement is shown below:
10 percent of the price of current DVDs.
Even when the new video standard begins to replace current
technologies, consumers won’t have to throw away their DVDs,
but they will need to invest in a new player. The industry is
planning to market backward-compatible drives with both blue
and red lasers, which will be able to play traditional DVDs and
CDs as well as Blu-ray discs.
                           Formats                                   In a configuration like this, a dumb terminal at an off-site office or
                                                                     store could “dial in” to a large, central computer. The 1960s were
Unlike DVDs and CDs, which started with read-only formats and
                                                                     the age of time-shared computers, so a business would often buy
only later added recordable and re-writable formats, Blu-ray is
                                                                     computer time from a time-share facility and connect to it via a
initially designed in several different formats:
                                                                     300-bit-per-second (bps) modem.
BD-ROM (read-only) - for pre-recorded content
BD-R (recordable) - for PC data storage                              A dumb terminal is simply a keyboard and a screen. A very
BD-RW (rewritable) - for PC data storage                             common dumb terminal at the time was called the DEC VT-100,
BD-RE (rewritable) - for HDTV recording                              and it became a standard of the day (now memorialized in terminal
                                                                     emulators worldwide). The VT-100 could display 25 lines of 80
                 Did You Say 500 GB?                                 characters each. When the user typed a character on the terminal,
It seems that the future holds a whole lot more than 25 to 54 GB     the modem sent the ASCII code for the character to the computer.
on a single disc. According to T3: Pioneer goes beyond Blu-Ray,      The computer then sent the character back to the computer so it
Pioneer is developing an optical disc that will blow away the hard   would appear on the screen.
disc in most of our PCs in terms storage capacity, holding 500 GB    When personal computers started appearing in the late 1970s,
of data. How so? Pioneer’s lasers are ultraviolet, which have an     bulletin board systems (BBS) became the rage. A person would
even shorter wavelength than the blue.                               set up a computer with a modem or two and some BBS software,
                                                                     and other people would dial in to connect to the bulletin board.
                                                                Page 89
The users would run terminal emulators on their computers to           these techniques (see the links at the end of this article for more
emulate a dumb terminal.                                               information).
People got along at 300 bps for quite a while. The reason this         Here’s a look inside a typical 56K modem:
speed was tolerable was because 300 bps represents about 30
characters per second, which is a lot more characters per second
than a person can type or read. Once people started transferring
large programs and images to and from bulletin board systems,
however, 300 bps became intolerable. Modem speeds went
through a series of steps at approximately two-year intervals:
300 bps - 1960s through 1983 or so
1200 bps - Gained popularity in 1984 and 1985
2400 bps
9600 bps - First appeared in late 1990 and early 1991
19.2 kilobits per second (Kbps)
28.8 Kbps
33.6 Kbps
56 Kbps - Became the standard in 1998
ADSL, with theoretical maximum of up to 8 megabits per
second (Mbps) - Gained popularity in 1999
(I’ll discuss How DSL Works and How Cable Modems Work                  All of these high-speed modems incorporate a concept of gradual
further on in this Chapter.)                                           degradation, meaning they can test the phone line and fall back to
                      300-bps Modems                                   slower speeds if the line cannot handle the modem’s fastest
We’ll use 300-bps modems as a starting point because they are
extremely easy to understand. A 300-bps modem is a device that         The next step in the evolution of the modem was asymmetric
uses frequency shift keying (FSK) to transmit digital information      digital subscriber line (ADSL) modems. The word asymmetric is
over a telephone line. In frequency shift keying, a different tone     used because these modems send data faster in one direction
(frequency) is used for the different bits).                           than they do in another. An ADSL modem takes advantage of the
                                                                       fact that any normal home, apartment or office has a dedicated
When a terminal’s modem dials a computer’s modem, the                  copper wire running between it and phone company’s nearest
terminal’s modem is called the originate modem. It transmits a         mux or central office. This dedicated copper wire can carry far
1,070-hertz tone for a 0 and a 1,270-hertz tone for a 1. The           more data than the 3,000-hertz signal needed for your phone’s
computer’s modem is called the answer modem, and it transmits a        voice channel. If both the phone company’s central office and
2,025-hertz tone for a 0 and a 2,225-hertz tone for a 1. Because the   your house are equipped with an ADSL modem on your line, then
originate and answer modems transmit different tones, they can         the section of copper wire between your house and the phone
use the line simultaneously. This is known as full-duplex opera-       company can act as a purely digital high-speed transmission
tion. Modems that can transmit in only one direction at a time are     channel. The capacity is something like 1 million bits per second
known as half-duplex modems, and they are rare.                        (Mbps) between the home and the phone company (upstream)
Let’s say that two 300-bps modems are connected, and the user at       and 8 Mbps between the phone company and the home (down-
the terminal types the letter “a.” The ASCII code for this letter is   stream) under ideal conditions. The same line can transmit both a
97 decimal or 01100001 binary (see How Bits and Bytes Work for         phone conversation and the digital data.
details on binary). A device inside the terminal called a UART         The approach an ADSL modem takes is very simple in principle.
(universal asynchronous receiver/transmitter) converts the byte        The phone line’s bandwidth between 24,000 hertz and 1,100,000
into its bits and sends them out one at a time through the             hertz is divided into 4,000-hertz bands, and a virtual modem is
terminal’s RS-232 port (also known as a serial port). The terminal’s   assigned to each band. Each of these 249 virtual modems tests its
modem is connected to the RS-232 port, so it receives the bits one     band and does the best it can with the slice of bandwidth it is
at a time and its job is to send them over the phone line.             allocated. The aggregate of the 249 virtual modems is the total
                       Faster Modems                                   speed of the pipe.

In order to create faster modems, modem designers had to use                             Point-to-Point Protocol
techniques far more sophisticated than frequency-shift keying.         Today, no one uses dumb terminals or terminal emulators to
First they moved to phase-shift keying (PSK), and then quadra-         connect to an individual computer. Instead, we use our modems
ture amplitude modulation (QAM). These techniques allow an             to connect to an Internet service provider (ISP), and the ISP
incredible amount of information to be crammed into the 3,000          connects us into the Internet. The Internet lets us connect to any
hertz of bandwidth available on a normal voice-grade phone line.       machine in the world. Because of the relationship between your
56K modems, which actually connect at something like 48 Kbps           computer, the ISP and the Internet, it is no longer appropriate to
on anything but absolutely perfect lines, are about the limit of       send individual characters. Instead, your modem is routing TCP/
                                                                       IP packets between you and your ISP.
                                                                Page 90
The standard technique for routing these packets through your          Putting both upstream and downstream data on the cable
modem is called the Point-to-Point Protocol (PPP). The basic idea      television system requires two types of equipment: a cable modem
is simple - your computer’s TCP/IP stack forms its TCP/IP              on the customer end and a cable modem termination system
datagrams normally, but then the datagrams are handed to the           (CMTS) at the cable provider’s end. Between these two types of
modem for transmission. The ISP receives each datagram and             equipment, all the computer networking, security and management
routes it appropriately onto the Internet. The same process occurs     of Internet access over cable television is put into place.
to get data from the ISP to your computer.
                                                                                       Inside the Cable Modem
If you want to know more about modems, protocols, and espe-
cially if you wish to delve into things like PSK and QAM in more       Cable modems can be either internal or external to the computer.
detail, check out the links on the next page!                          In some cases, the cable modem can be part of a set-top cable box,
                                                                       requiring that only a keyboard and mouse be added for Internet
               How Cable Modems Work                                   access. In fact, if your cable system has upgraded to digital cable,
                                                                       the new set-top box the cable company provides will be capable
For millions of people, television brings news, entertainment and
                                                                       of connecting to the Internet, whether or not you receive Internet
educational programs into their homes. Many people get their TV
                                                                       access through your CATV connection. Regardless of their
signal from cable television (CATV) because cable TV provides a
                                                                       outward appearance, all cable modems contain certain key
clearer picture and more channels.
Many people who have cable TV can now get a high-speed                 A   tuner
connection to the Internet from their cable provider. Cable            A   demodulator
modems compete with technologies like asymmetrical digital             A   modulator
subscriber lines (ADSL). If you have ever wondered what the            A   media access control (MAC) device
differences between DSL and cable modems are, or if you have           A   microprocessor
ever wondered how a computer network can share a cable with
dozens of television channels, then read on. In this tutorial, we’ll
look at how a cable modem works and see how 100 cable televi-
sion channels and other stuff can flow over a single coaxial cable
into your home.
                         Extra Space
You might think that a television channel would take up quite a bit
of electrical “space,” or bandwidth, on a cable. In reality, each
television signal is given a 6-megahertz (MHz, millions of cycles
per second) channel on the cable. The coaxial cable used to carry
cable television can carry hundreds of megahertz of signals - all
the channels you could want to watch and more.                                                       Tuner
In a cable TV system, signals from the various channels are each       The tuner connects to the cable outlet, sometimes with the
given a 6-MHz slice of the cable’s available bandwidth and then        addition of a splitter that separates the Internet data channel from
sent down the cable to your house. In some systems, coaxial            normal CATV programming. Since the Internet data comes
cable is the only medium used for distributing signals. In other       through an otherwise unused cable channel, the tuner simply
systems, fiber-optic cable goes from the cable company to              receives the modulated digital signal and passes it to the demodu-
different neighborhoods or areas. Then the fiber is terminated and     lator.
the signals move onto coaxial cable for distribution to individual     In some cases, the tuner will contain a diplexer, which allows the
houses. When a cable company offers Internet access over the           tuner to make use of one set of frequencies (generally between 42
cable, Internet information can use the same cables because the        and 850 MHz) for downstream traffic, and another set of frequen-
cable modem system puts downstream data - data sent from the           cies (between 5 and 42 MHz) for the upstream data. Other
Internet to an individual computer - into a 6-MHz channel. On the      systems, most often those with more limited capacity for chan-
cable, the data looks just like a TV channel. So Internet down-        nels, will use the cable modem tuner for downstream data and a
stream data takes up the same amount of cable space as any             dial-up telephone modem for upstream traffic. In either case, after
single channel of programming. Upstream data - information sent        the tuner receives a signal, it is passed to the demodulator.
from an individual back to the Internet - requires even less of the
cable’s bandwidth, just 2 MHz, since the assumption is that most                                Demodulator
people download far more information than they upload.                 The most common demodulators have four functions. A quadra-
                                                                       ture amplitude modulation (QAM) demodulator takes a radio-
                                                                       frequency signal that has had information encoded in it by
                                                                       varying both the amplitude and phase of the wave, and turns it
                                                                       into a simple signal that can be processed by the analog-to-digital
                                                                       (A/D) converter. The A/D converter takes the signal, which varies
                                                                       in voltage, and turns it into a series of digital 1s and 0s. An error
                                                               Page 91
correction module then checks the received information against a
known standard, so that problems in transmission can be found
and fixed. In most cases, the network frames, or groups of data,
are in MPEG format, so an MPEG synchronizer is used to make
sure the data groups stay in line and in order.
In cable modems that use the cable system for upstream traffic, a
modulator is used to convert the digital computer network data
into radio-frequency signals for transmission. This component is
sometimes called a burst modulator, because of the irregular
nature of most traffic between a user and the Internet, and
consists of three parts:
* A section to insert information used for error correction on the
  receiving end
* A QAM modulator
* A digital-to-analog (D/A) converter                                  or not. On the upstream side, information is sent from the user to
             Media Access Control (MAC)                                the CMTS - other users don’t see that data at all. The narrower
                                                                       upstream bandwidth is divided into slices of time, measured in
The MAC sits between the upstream and downstream portions of           milliseconds, in which users can transmit one “burst” at a time to
the cable modem, and acts as the interface between the hardware        the Internet. The division by time works well for the very short
and software portions of the various network protocols. All            commands, queries and addresses that form the bulk of most
computer network devices have MACs, but in the case of a cable         users’ traffic back to the Internet.
modem the tasks are more complex than those of a normal network
interface card. For this reason, in most cases, some of the MAC        A CMTS will enable as many as 1,000 users to connect to the
functions will be assigned to a central processing unit (CPU) -        Internet through a single 6-MHz channel. Since a single channel is
either the CPU in the cable modem or the CPU of the user’s             capable of 30 to 40 megabits per second (Mbps) of total through-
system.                                                                put, this means that users may see far better performance than is
                                                                       available with standard dial-up modems. The single channel
                       Microprocessor                                  aspect, though, can also lead to one of the issues some users
                                                                       experience with cable modems.
The microprocessor’s job depends somewhat on whether the
cable modem is designed to be part of a larger computer system or      If you are one of the first users to connect to the Internet through
to provide Internet access with no additional computer support.        a particular cable channel, then you may have nearly the entire
In situations calling for an attached computer, the internal           bandwidth of the channel available for your use. As new users,
microprocessor still picks up much of the MAC function from the        especially heavy-access users, are connected to the channel, you
dedicated MAC module. In systems where the cable modem is the          will have to share that bandwidth, and may see your performance
sole unit required for Internet access, the microprocessor picks up    degrade as a result. It is possible that, in times of heavy usage
MAC slack and much more. In either case, Motorola’s PowerPC            with many connected users, performance will be far below the
processor is one of the common choices for system designers.           theoretical maximums. The good news is that this particular
                                                                       performance issue can be resolved by the cable company adding
          Cable Modem Termination System
                                                                       a new channel and splitting the base of users.
At the cable provider’s head-end, the CMTS provides many of
                                                                       Another benefit of the cable modem for Internet access is that,
the same functions provided by the DSLAM in a DSL system.
                                                                       unlike ADSL, its performance doesn’t depend on distance from
The CMTS takes the traffic coming in from a group of customers
                                                                       the central cable office. A digital CATV system is designed to
on a single channel and routes it to an Internet service provider
                                                                       provide digital signals at a particular quality to customer house-
(ISP) for connection to the Internet. At the head-end, the cable
                                                                       holds. On the upstream side, the burst modulator in cable modems
providers will have, or lease space for a third-party ISP to have,
                                                                       is programmed with the distance from the head-end, and provides
servers for accounting and logging, Dynamic Host Configuration
                                                                       the proper signal strength for accurate transmission.
Protocol (DHCP) for assigning and administering the IP addresses
of all the cable system’s users, and control servers for a protocol                         How DSL Works
called CableLabs Certified Cable Modems — formerly Data Over
Cable Service Interface Specifications (DOCSIS), the major             When you connect to the Internet, you might connect through a
standard used by U.S. cable systems in providing Internet access       regular modem, through a local-area network connection in your
to users.                                                              office, through a cable modem or through a digital subscriber line
                                                                       (DSL) connection. DSL is a very high-speed connection that uses
The downstream information flows to all connected users, just like     the same wires as a regular telephone line.
in an Ethernet network - it’s up to the individual network connec-
tion to decide whether a particular block of data is intended for it
                                                               Page 92
                                                                       ways that POTS makes the most of the telephone company’s
                                                                       wires and equipment is by limiting the frequencies that the
                                                                       switches, telephones and other equipment will carry. Human
                                                                       voices, speaking in normal conversational tones, can be carried in
                                                                       a frequency range of 0 to 3,400 Hertz (cycles per second — see
                                                                       How Telephones Work for a great demonstration of this). This
                                                                       range of frequencies is tiny. For example, compare this to the
                                                                       range of most stereo speakers, which cover from roughly 20 Hertz
                                                                       to 20,000 Hertz. And the wires themselves have the potential to
                                                                       handle frequencies up to several million Hertz in most cases. The
                                                                       use of such a small portion of the wire’s total bandwidth is
                                                                       historical — remember that the telephone system has been in
                                                                       place, using a pair of copper wires to each home, for about a
                                                                       century. By limiting the frequencies carried over the lines, the
                                                                       telephone system can pack lots of wires into a very small space
                                                                       without worrying about interference between lines. Modern
                                                                       equipment that sends digital rather than analog data can safely
                                                                       use much more of the telephone line’s capacity. DSL does just
                                                                       Most homes and small business users are connected to an
                                                                       asymmetric DSL (ADSL) line. ADSL divides up the available
                                                                       frequencies in a line on the assumption that most Internet users
         Here are some advantages of DSL                               look at, or download, much more information than they send, or
                                                                       upload. Under this assumption, if the connection speed from the
* You can leave your Internet connection open and still use the
                                                                       Internet to the user is three to four times faster than the connec-
  phone line for voice calls.
                                                                       tion from the user back to the Internet, then the user will see the
* The speed is much higher than a regular modem (1.5 Mbps vs.
                                                                       most benefit (most of the time).
  56 Kbps)
* DSL doesn’t necessarily require new wiring; it can use the                                  Voice and Data
  phone line you already have.
* The company that offers DSL will usually provide the modem           Precisely how much benefit you see will greatly depend on how
  as part of the installation.                                         far you are from the central office of the company providing the
                                                                       ADSL service. ADSL is a distance-sensitive technology: As the
              But there are disadvantages                              connection’s length increases, the signal quality decreases and
* A DSL connection works better when you are closer to the             the connection speed goes down. The limit for ADSL service is
 provider’s central office.                                            18,000 feet (5,460 meters), though for speed and quality of service
* The connection is faster for receiving data than it is for sending   reasons many ADSL providers place a lower limit on the distances
  data over the Internet.                                              for the service. At the extremes of the distance limits, ADSL
* The service is not available everywhere.                             customers may see speeds far below the promised maximums,
                                                                       while customers nearer the central office have faster connections
In this tutorial, I’ll explain how a DSL connection manages to         and may see extremely high speeds in the future. ADSL technol-
squeeze more information through a standard phone line - and lets      ogy can provide maximum downstream (Internet to customer)
you make regular telephone calls even when you’re online!              speeds of up to 8 megabits per second (Mbps) at a distance of
               Skinny Voice, Broad Band                                about 6,000 feet (1,820 meters), and upstream speeds of up to 640
                                                                       kilobits per second (Kbps). In practice, the best speeds widely
If you have read How Telephones Work, then you know that a             offered today are 1.5 Mbps downstream, with upstream speeds
standard telephone installation in the United States consists of a     varying between 64 and 640 Kbps.
pair of copper wires that the phone company installs in your
                                                                       You might wonder, if distance is a limitation for DSL, why it’s not
home. The copper wires have lots of room for carrying more than
                                                                       also a limitation for voice telephone calls. The answer lies in small
your phone conversations - they are capable of handling a much
                                                                       amplifiers called loading coils that the telephone company uses to
greater bandwidth, or range of frequencies, than that demanded
                                                                       boost voice signals. Unfortunately, these loading coils are
for voice. DSL exploits this “extra capacity” to carry information
                                                                       incompatible with ADSL signals, so a voice coil in the loop
on the wire without disturbing the line’s ability to carry conversa-
                                                                       between your telephone and the telephone company’s central
tions. The entire plan is based on matching particular frequencies
                                                                       office will disqualify you from receiving ADSL. Other factors that
to specific tasks.
                                                                       might disqualify you from receiving ADSL include:
To understand DSL, you first need to know a couple of things           * Bridge taps - These are extensions, between you and the
about a normal telephone line — the kind that telephone profes-          central office, that extend service to other customers. While
sionals call POTS, for Plain Old Telephone Service. One of the
                                                               Page 93
   you wouldn’t notice these bridge taps in normal phone service,      KHz wide. One way to think about it is to imagine that the phone
   they may take the total length of the circuit beyond the distance   company divides your copper line into 247 different 4-KHz lines
  limits of the service provider.                                      and then attaches a modem to each one. You get the equivalent of
* Fiber-optic cables - ADSL signals can’t pass through the             247 modems connected to your computer at once! Each channel is
  conversion from analog to digital and back to analog that            monitored and, if the quality is too impaired, the signal is shifted
  occurs if a portion of your telephone circuit comes through          to another channel. This system constantly shifts signals
  fiber-optic cables.                                                  between different channels, searching for the best channels for
* Distance - Even if you know where your central office is (don’t      transmission and reception. In addition, some of the lower
   be surprised if you don’t - the telephone companies don’t           channels (those starting at about 8 KHz), are used as bidirectional
  advertise their locations), looking at a map is no indication of     channels, for upstream and downstream information. Monitoring
   the distance a signal must travel between your house and the        and sorting out the information on the bidirectional channels, and
  office.                                                              keeping up with the quality of all 247 channels, makes DMT more
                                                                       complex to implement than CAP, but gives it more flexibility on
                  Other Types of DSL                                   lines of differing quality.
Very high bit-rate DSL (VDSL) - This is a fast connection, but
 works only over a short distance.
Symmetric DSL (SDSL) - This connection, used mainly by small
  businesses, doesn’t allow you to use the phone at the same
 time, but the speed of receiving and sending data is the same.
Rate-adaptive DSL (RADSL) - This is a variation of ADSL, but           CAP and DMT are similar in one way that you can see as a DSL
 the modem can adjust the speed of the connection depending            user. If you have ADSL installed, you were almost certainly given
 on the length and quality of the line.                                small filters to attach to the outlets that don’t provide the signal
                   Splitting the Signal                                to your ADSL modem. These filters are low-pass filters — simple
                                                                       filters that block all signals above a certain frequency. Since all
There are two competing and incompatible standards for ADSL.           voice conversations take place below 4 KHz, the low-pass (LP)
The official ANSI standard for ADSL is a system called discrete        filters are built to block everything above 4 KHz, preventing the
multitone, or DMT. According to equipment manufacturers, most          data signals from interfering with standard telephone calls.
of the ADSL equipment installed today uses DMT. An earlier and
more easily implemented standard was the carrierless amplitude/                               DSL Equipment
phase (CAP) system, which was used on many of the early                ADSL uses two pieces of equipment, one on the customer end
installations of ADSL.                                                 and one at the Internet service provider, telephone company or
                                                                       other provider of DSL services. At the customer’s location there
                                                                       is a DSL transceiver, which may also provide other services. The
                                                                       DSL service provider has a DSL Access Multiplexer (DSLAM) to
                                                                       receive customer connections.

CAP operates by dividing the signals on the telephone line into
three distinct bands: Voice conversations are carried in the 0 to 4
KHz (kilohertz) band, as they are in all POTS circuits. The
upstream channel (from the user back to the server) is carried in a
band between 25 and 160 KHz. The downstream channel (from the
server to the user) begins at 240 KHz and goes up to a point that
varies depending on a number of conditions (line length, line
noise, number of users in a particular telephone company switch)
but has a maximum of about 1.5 MHz (megahertz). This system,
with the three channels widely separated, minimizes the possibil-
ity of interference between the channels on one line, or between
the signals on different lines.

DMT also divides signals into separate channels, but doesn’t use
two fairly broad channels for upstream and downstream data.
Instead, DMT divides the data into 247 separate channels, each 4
                                                            Page 94
                    DSL Transceiver
                                                                           Good Boot Guide to Your USB
Most residential customers call their DSL transceiver a “DSL
modem.” The engineers at the telephone company or ISP call it an
ATU-R. Regardless of what it’s called, it’s the point where data                                        Just about any computer that
from the user’s computer or network is connected to the DSL line.                                       you buy today comes with one
The transceiver can connect to a customer’s equipment in several                                        or more Universal Serial Bus
ways, though most residential installation uses USB or 10 base-T                                        connectors on the back. These
Ethernet connections. While most of the ADSL transceivers sold                                          USB connectors let you attach
by ISPs and telephone companies are simply transceivers, the                                            everything from mice to
devices used by businesses may combine network routers,                                                 printers to your computer
network switches or other networking equipment in the same                                              quickly and easily. The
platform.                                                                                               operating system supports
                                                                    USB as well, so the installation of the device drivers is quick and
                           DSLAM                                    easy, too. Compared to other ways of connecting devices to your
                                                                    computer (including parallel ports, serial ports and special cards
The DSLAM at the access provider is the equipment that really
                                                                    that you install inside the computer’s case), USB devices are
allows DSL to happen. A DSLAM takes connections from many
                                                                    incredibly simple!
customers and aggregates them onto a single, high-capacity
connection to the Internet. DSLAMs are generally flexible and       In this Chapter, we’ll look at USB ports from both a user and a
able to support multiple types of DSL in a single central office,   technical standpoint. You will learn why the USB system is so
and different varieties of protocol and modulation - both CAP and   flexible and how it is able to support so many devices so easily -
DMT, for example - in the same type of DSL. In addition, the        it’s truly an amazing system!
                                                                                           What is USB?
DSLAM may provide additional functions including routing or
dynamic IP address assignment for the customers.
The DSLAM provides one of the main differences between user         Anyone who has been around computers for more that two or
service through ADSL and through cable modems. Because              three years knows the problem that the Universal Serial Bus is
cable-modem users generally share a network loop that runs          trying to solve - in the past, connecting devices to computers has
through a neighborhood, adding users means lowering perfor-         been a real headache!
mance in many instances. ADSL provides a dedicated connection       Printers connected to parallel printer ports, and most computers
from each user back to the DSLAM, meaning that users won’t see      only came with one. Things like Zip drives, which need a high-
a performance decrease as new users are added — until the total     speed connection into the computer, would use the parallel port
number of users begins to saturate the single, high-speed           as well, often with limited success and not much speed.
connection to the Internet. At that point, an upgrade by the
                                                                    Modems used the serial port, but so did some printers and a
service provider can provide additional performance for all the
                                                                    variety of odd things like Palm Pilots and digital cameras. Most
users connected to the DSLAM.
                                                                    computers have at most two serial ports, and they are very slow in
                        DSL Future                                  most cases.
ADSL is competing with technologies such as cable-modem             Devices that needed faster connections came with their own
access and satellite Internet access for high-speed connections     cards, which had to fit in a card slot inside the computer’s case.
from consumers to the Internet. According to IDC, a market-         Unfortunately, the number of card slots is limited and you needed
analysis firm based in Framingham, MA, approximately 330,000        a Ph.D. to install the software for some of the cards.
households in the United States were connected to the Internet      The goal of USB is to end all of these headaches. The Universal
via DSL in 1999, compared to 1,350,000 households with cable        Serial Bus gives you a single, standardized, easy-to-use way to
modems. By 2003, IDC estimates that the number of households        connect up to 127 devices to a computer. Each device can
with cable modems will have risen to 8,980,000, while DSL will      consume up to a maximum of 6 megabits per second (Mbps) of
have raced into the broadband lead with 9,300,000 households.       bandwidth, which is fast enough for the vast majority of periph-
Currently, ADSL is limited (by U.S. Federal Communications          eral devices that most people want to connect to their machines.
Commission regulations) to a maximum of 1.5 megabits per            Just about every peripheral made now comes in a USB version. A
second. Current technology can provide a theoretical maximum of     sample list of USB devices that you can buy today includes:
up to 7 megabits per second, and research promises even greater
                                                                    * Printers * Scanners * Mice * Joysticks * Flight yokes
performance in the future with protocols like G.Lite and VDSL.
                                                                    * Modems * Digital cameras * Webcams * Scientific data
                                                                    * acquisition devices * Speakers * Telephones * Video phones
          It’s your choice - Cable or DSL.
                                                                    * Storage devices such as Zip drives * Network connections.
  But in my opinion, there’s only one choice - Cable
                                                                    Connecting a USB device to a computer is simple - you find the
                                                                    USB connector on the back of your machine and plug the USB
                                                                    connector into it.
                                                               Page 95
                                                                       By using different connectors on the upstream and downstream
                                                                       end, it is impossible to ever get confused - if you connect any
                                                                       USB cable’s “B” connector into a device, you know that it will
                                                                       work. Similarly, you can plug any “A” connector into any “A”
                                                                       socket and know that it will work.
                                                                                        Running Out of Ports?
                                                                       Most computers that you buy today come with one or two USB
                                                                       sockets. With so many USB devices on the market today, you
                                                                       easily run out of sockets very quickly. For example, on the
                                                                       computer that I am typing on right now, I have a USB printer, a
                                                                       USB scanner, a USB Webcam and a USB network connection. My
                                                                       computer has only one USB connector on it, so the obvious
                                                                       question is, “How do you hook up all the devices?”
                                                                       The easy solution to the problem is to buy an inexpensive USB
                                                                       hub. The USB standard supports up to 127 devices, and USB
                                                                       hubs are a part of the standard.
The rectangular socket is a typical USB socket on the back
of the computer.

             A typical USB connector for a device
                    called an “A” connection
If it is a new device, the operating system auto-detects it and asks
for the driver disk. If the device has already been installed, the
computer activates it and starts talking to it. USB devices can be
connected and disconnected at any time.
Many USB devices come with their own built-in cable, and the
cable has an “A” connection on it. If not, then the device has a
socket on it that accepts a USB “B” connector.

                                                                         A typical USB four-port hub accepts 4 “A” connections.
                                                                       A hub typically has four new ports, but may have many more.
                                                                       You plug the hub into your computer, and then plug your devices
                                                                       (or other hubs) into the hub. By chaining hubs together, you can
                                                                       build up dozens of available USB ports on a single computer.
                                                                       Hubs can be powered or unpowered. As you will see on the next
                    A typical “B” connection                           page, the USB standard allows for devices to draw their power
                                                                       from their USB connection. Obviously, a high-power device like a
The USB standard uses “A” and “B” connectors to avoid                  printer or scanner will have its own power supply, but low-power
confusion:                                                             devices like mice and digital cameras get their power from the bus
* “A” connectors head “upstream” toward the computer.                  in order to simplify them. The power (up to 500 milliamps at 5
* “B” connectors head “downstream” and connect to individual           volts) comes from the computer. If you have lots of self-powered
  devices.                                                             devices (like printers and scanners), then your hub does not need
                                                                       to be powered — none of the devices connecting to the hub
                                                            Page 96
needs additional power, so the computer can handle it. If you       * Isochronous - A streaming device (such as speakers) uses the
have lots of unpowered devices like mice and cameras, you            isochronous mode. Data streams between the device and the
probably need a powered hub. The hub has its own transformer         host in real-time, and there is no error correction.
and it supplies power to the bus so that the devices do not
                                                                    The host can also send commands or query parameters with
overload the computer’s supply.                                     control packets.
                   Behind the Scenes                                As devices are enumerated, the host is keeping track of the total
The Universal Serial Bus has the following features:                bandwidth that all of the isochronous and interrupt devices are
                                                                    requesting. They can consume up to 90 percent of the 12 Mbps of
* The computer acts as the host.
                                                                    bandwidth that is available. After 90 percent is used up, the host
* Up to 127 devices can connect to the host, either directly or
                                                                    denies access to any other isochronous or interrupt devices.
  by way of USB hubs.
                                                                    Control packets and packets for bulk transfers use any bandwidth
* Individual USB cables can run as long as 5 meters; with hubs,
                                                                    left over (at least 10 percent).
  devices can be up to 30 meters (six cables’ worth) away from
  the host.                                                         The Universal Serial Bus divides the available bandwidth into
* The bus has a maximum data rate of 12 megabits per second.        frames, and the host controls the frames. Frames contain 1,500
* Any individual device can request up to 6 megabits per second     bytes, and a new frame starts every millisecond. During a frame,
  (obviously, you cannot really have more than one device           isochronous and interrupt devices get a slot so they are guaran-
  requesting 6 Mbps or you would exceed the 12-Mbps maxi-           teed the bandwidth they need. Bulk and control transfers use
  mum for the bus).                                                 whatever space is left. The technical links at the end of the article
* A USB cable has two wires for power (+5 volts and ground)         contain lots of detail if you would like to learn more.
  and a twisted pair of wires to carry the data.
                                                                                               The Future
* On the power wires, the computer can supply up to 500
 milliamps of power at 5 volts.                                     The USB 2.0 spec promises a speed increase by a factor of 10 or
* Low-power devices (such as mice) can draw their power             20, while maintaining backward compatibility with older devices
  directly from the bus. High-power devices (such as printers)      and using the same cables. This sort of speed will make it possible
  have their own power supplies and draw minimal power from         to connect almost anything to your computer via USB, including
  the bus. Hubs can have their own power supplies to provide        external hard drives and video cameras. The future looks bright!
  power to devices connected to the hub.
* USB devices are hot-swappable, meaning you can plug them
  into the bus and unplug them any time.                            You have probably heard the term FireWire if you have any
* Many USB devices can be put to sleep by the host computer         interest in digital video - or maybe you know it as Sony i.Link or
  when the computer enters a power-saving mode.                     as IEEE 1394, the offical name for the standard. FireWire is a way
The devices connected to a USB port rely on the USB cable to        to connect different pieces of equipment so they can easily and
carry power and data.                                               quickly share information.
                                                                    Originally created by Apple and standardized in 1995 as the
                                                                    specification IEEE 1394 High Performance Serial Bus, FireWire is
                                                                    very similar to Universal Serial Bus (USB). The designers of
                                                                    FireWire, which actually precedes the development of USB, had
                                                                    several particular goals in mind when they created the standard:
                                                                    * Fast transfer of data (up to 400 Mbps)
Inside a USB cable: There are two wires for power - +5              * Lots of devices on the bus
volts (red) and ground (brown) - and a twisted pair (yellow         * Ease of use
and blue) of wires to carry the data. The cable is also             * Hot pluggable
shielded.                                                           * Provide power through the cable
When the host powers up, it queries all of the devices connected    * Plug-and-play
to the bus and assigns each one an address. This process is         * Low cabling cost
called enumeration - devices are also enumerated when they          * Low implementation cost
connect to the bus. The host also finds out from each device what   So let’s learn exactly what FireWire is, how it is used and why you
type of data transfer it wishes to perform:                         want it.
* Interrupt - A device like a mouse or a keyboard, which will be
  sending very little data, would choose the interrupt mode.                              FireWire Basics
* Bulk - A device like a printer, which receives data in one big    When the host computer powers up, it queries all of the devices
  packet, uses the bulk transfer mode. A block of data is sent to   connected to the bus and assigns each one an address, a process
  the printer (in 64-byte chunks) and verified to make sure it is   called enumeration. FireWire is plug-and-play, so if a new
  correct.                                                          FireWire device is connected to a computer, the operating system
                                                               Page 97
auto-detects it and asks for the driver disk. If the device has                             Here’s a summary:
already been installed, the computer activates it and starts talking
to it. FireWire devices are hot pluggable, which means they can
be connected and disconnected at any time, even with the power
FireWire uses 64-bit fixed addressing, based on the IEEE 1212
standard. There are three parts to each packet of information sent
by a device over FireWire:
* A 10-bit bus ID that is used to determine which FireWire bus
  the data came from
* A 6-bit physical ID that identifies which device on the bus sent
  the data
* A 48-bit storage area that is capable of addressing 256
  terabytes of information for each node!
                                                                       As you can see, the two are remarkably alike. Implementing
The bus ID and physical ID together comprise the 16-bit node ID,
                                                                       FireWire costs a little more than USB, which led to the adoption of
which allows for 64,000 nodes on a system. Individual FireWire
                                                                       USB as the standard for connecting most peripherals that do not
cables can run as long as 4.5 meters. Data can be sent through up
                                                                       require a high-speed bus.
to 16 hops for a total maximum distance of 72 meters. Hops occur
when devices are daisy-chained together. Look at the example           USB 2.0, released in 2001 and becoming popular in 2002, is
below. The camcorder is connected to the external hard drive           designed to offer performance similar to FireWire. USB 2.0 has a
connected to Computer A. Computer A is connected to Computer           maximum data rate of 480 Mbps. Given that their speeds are now
B, which in turn is connected to Computer C. It takes four hops        roughly identical, the big difference remaining between FireWire
for Computer C to access the camera.                                   and USB 2.0 is that USB 2.0 is host-based, meaning that devices
                                                                       must connect to a computer in order to communicate. FireWire is
                                                                       peer-to-peer, meaning that two FireWire cameras can talk to each
                                                                       other without going through a computer.
                                                                       Of course, FireWire has an answer to USB 2.0 in its upcoming
                                                                       IEEE 1394b, which will up the ante with transfer speeds starting at
                                                                       800 Mbps and predicted to reach an unbelievable 3.2 gigabits per
FireWire devices can be powered or unpowered. FireWire allows          second when the current copper FireWire cables are replaced with
devices to draw their power from their connection. Two power           fiber optics.
conductors in the cable can supply power (8 to 40 volts, 1.5 amps
                                                                                                Digital Video
maximum) from the computer to an unpowered device. Obviously,
a high-power device like an external hard drive will have its own      FireWire really shines when it comes to digital video applications.
power supply, but low-power devices like digital still cameras can     Most digital video cameras or camcorders now have a FireWire
get their power from the bus in order to simplify them. Two            plug. When you attach a camcorder to a computer using FireWire,
twisted pair sets carry the data in a FireWire cable.                  the connection is amazing!
                                                                       An important element of FireWire is the support of isochronous
                                                                       devices. In isochronous mode, data streams between the device
                                                                       and the host in real-time with guaranteed bandwidth and no error
                                                                       correction. Essentially, this means that a device like a digital
                                                                       camcorder can request that the host computer allocate enough
                                                                       bandwidth for the camcorder to send uncompressed video in real-
                    FireWire vs. USB                                   time to the computer. When the computer/camera FireWire
                                                                       connection enters isochronous mode, the camera can send the
The key difference between FireWire and USB is that FireWire is        video in a steady flow to the computer without anything disrupt-
intended for devices working with a lot more data — things like        ing the process.
camcorders, DVD players and digital audio equipment. FireWire
and USB share a number of characteristics and differ in some           You can easily edit and create custom video projects using fast
important ways.                                                        hard drives, a digital camcorder and a computer. With the right
                                                                       software, the computer and the camera communicate, and the
                                                                       computer can download all of the video automatically and with
                                                                       perfect digital clarity. Since the content is digital from start to
                                                                       finish, there is no loss of quality as you work on successive
                                                               Page 98
                                                                      through the floating gate. If the flow through the gate is greater
            Good Boot Guide to Your                                   than 50 percent of the charge, it has a value of 1. When the
                 Flash Memory                                         charge passing through drops below the 50-percent threshold,
                                                                      the value changes to 0. A blank EEPROM has all of the gates
                                                                      fully open, giving each cell a value of 1.
                                                                      The electrons in the cells of a Flash-memory chip can be returned
                                                                      to normal (“1”) by the application of an electric field, a higher-
                                                                      voltage charge. Flash memory uses in-circuit wiring to apply the
                                                                      electric field either to the entire chip or to predetermined sections
                                                                      known as blocks. This erases the targeted area of the chip, which
                                                                      can then be rewritten. Flash memory works much faster than
                                                                      traditional EEPROMs because instead of erasing one byte at a
Electronic memory comes in a variety of forms to serve a variety      time, it erases a block or the entire chip, and then rewrites it.
of purposes. Flash memory is used for easy and fast information
                                                                      You may think that your car radio has Flash memory, since you
storage in such devices as digital cameras and home video game
                                                                      are able to program the presets and the radio remembers them.
consoles. It is used more as a hard drive than as RAM. In fact,
                                                                      But it is actually using Flash RAM. The difference is that Flash
Flash memory is considered a solid state storage device. Solid
                                                                      RAM has to have some power to maintain its contents, while
state means that there are no moving parts - everything is
                                                                      Flash memory will maintain its data without any external source
electronic instead of mechanical.
                                                                      of power. Even though you have turned the power off, the car
Here are a few examples of Flash memory:                              radio is pulling a tiny amount of current to preserve the data in
* Your computer’s BIOS chip                                           the Flash RAM. That is why the radio will lose its presets if your
* CompactFlash (most often found in digital cameras)                  car battery dies or the wires are disconnected.
* SmartMedia (most often found in digital cameras)                              Removable Flash Memory Cards
* Memory Stick (most often found in digital cameras)
* PCMCIA Type I and Type II memory cards (used as solid-state         While your computer’s BIOS chip is the most common form of
  disks in laptops)                                                   Flash memory, removable solid-state storage devices are becom-
* Memory cards for video game consoles                                ing increasingly popular. SmartMedia and CompactFlash cards
                                                                      are both well-known, especially as “electronic film” for digital
In this Chapter, we’ll find out how Flash memory works and look
                                                                      cameras. Other removable Flash memory products include Sony’s
at some of the forms it takes and types of devices that use it.
                                                                      Memory Stick, PCMCIA memory cards, and memory cards for
                         Flash Basics                                 video game systems such as Nintendo’s N64, Sega’s Dreamcast
                                                                      and Sony’s PlayStation. We will focus on SmartMedia and
We discussed the underlying technology of Flash memory in             CompactFlash, but the essential idea is the same for all of these
How ROM Works, but here’s a quick review:                             products. Every one of them is simply a form of Flash memory.
Flash memory is a type of EEPROM chip. It has a grid of columns
and rows with a cell that has two transistors at each intersection    There are several reasons to use Flash memory instead of a hard
The two transistors are separated from each other by a thin oxide     * Flash memory is noiseless * * It allows faster access
layer. One of the transistors is known as a floating gate, and the    * It is smaller in size * It is lighter * It has no moving parts.
other one is the control gate. The floating gate’s only link to the
row, or wordline, is through the control gate. As long as this link   So why don’t we just use Flash memory for everything? Because
is in place, the cell has a value of 1. To change the value to a 0    the cost per megabyte for a hard disk is drastically cheaper, and
requires a curious process called Fowler-Nordheim tunneling.          the capacity is substantially more.

                           Tunneling                                                           SmartMedia
Tunneling is used to alter the placement of electrons in the          The solid-state floppy-disk card (SSFDC), better known as
floating gate. An electrical charge, usually 10 to 13 volts, is       SmartMedia, was originally developed by Toshiba.
applied to the floating gate. The charge comes from the column,       SmartMedia cards are available in capacities ranging from 2 MB
or bitline, enters the floating gate and drains to a ground.          to 128 MB. The card itself is quite small, approximately 45 mm
This charge causes the floating-gate transistor to act like an        long, 37 mm wide and less than 1 mm thick. This is amazing when
electron gun. The excited electrons are pushed through and            you consider what is packed into such a tiny package!
trapped on other side of the thin oxide layer, giving it a negative   As shown below, SmartMedia cards are elegant in their simplicity.
charge. These negatively charged electrons act as a barrier           A plane electrode is connected to the Flash-memory chip by
between the control gate and the floating gate. A special device      bonding wires. The Flash-memory chip, plane electrode and
called a cell sensor monitors the level of the charge passing         bonding wires are embedded in a resin using a technique called
                                                                 Page 99
                                                                         As shown below, CompactFlash cards are 43 mm wide and 36 mm
                                                                         long, and come in two thicknesses: Type I cards are 3.3 mm thick,
                                                                         and Type II cards are 5.5 mm thick.

                        SmartMedia card
over-molded thin package (OMTP). This allows everything to be
integrated into a single package without the need for soldering.
                                                                                               CompactFlash card
                                                                         CompactFlash cards support dual voltage and will operate at
                                                                         either 3.3 volts or 5 volts.
                                                                         The increased thickness of the card allows for greater storage
                                                                         capacity than SmartMedia cards. CompactFlash sizes range from
                                                                         8 MB to 6GB. The onboard controller can increase performance,
                                                                         particularly on devices that have slow processors. The case and
                                                                         controller chip add size, weight and complexity to the
                                                                         CompactFlash card when compared to the SmartMedia card.
                                                                                            Memory Standards
                                                                         Both SmartMedia and CompactFlash, as well as PCMCIA Type I
                                                                         and Type II memory cards, adhere to standards developed by the
                                                                         Personal Computer Memory Card International Association
                                                                         (PCMCIA). Because of these standards, it is easy to use
The OMTP module is glued to a base card to create the actual             CompactFlash and SmartMedia products in a variety of devices.
card. Power and data is carried by the electrode to the Flash-           You can also buy adapters that allow you to access these cards
memory chip when the card is inserted into a device. A notched           through a standard floppy drive, USB port or PCMCIA card slot
corner indicates the power requirements of the SmartMedia card.          (like the one you find on a laptop computer). Sony’s Memory
Looking at the card with the electrode facing up, if the notch is        Stick is available in a large array of products offered by Sony, and
on the left side, the card needs 5 volts. If the notch is on the right   is now showing up in products from other manufacturers as well.
side, it requires 3.3 volts.
                                                                         Although standards are flourishing, there are many Flash-
SmartMedia cards erase, write and read memory in small blocks            memory products that are completely proprietary in nature, such
(256- or 512-byte increments). This approach means that they are         as the memory cards in video game systems. But it is good to
capable of fast, reliable performance while allowing you to              know that as electronic components become increasingly
specify which data you wish to keep. They are small, lightweight         interchangeable and learn to communicate with each other (by
and easy to use. They are less rugged than other forms of                way of technologies such as Bluetooth), standardized removable
removable solid-state storage, so you should be very careful             memory will allow you to keep your world close at hand.
when handling and storing them.
CompactFlash cards were developed by Sandisk in 1994, and
they are different from SmartMedia cards in two important ways:
* They are thicker.
* They utilize a controller chip.
CompactFlash consists of a small circuit board with Flash-
memory chips and a dedicated controller chip, all encased in a
rugged shell that is several times thicker than a SmartMedia card.
                                                                 Page 100
                                                                          Let’s break that down: 1.4 million bits per second equals 176,000
   Good Boot Guide to Your MP3 Files                                      bytes per second. If an average song is three minutes long, then
                                                                          the average song on a CD consumes about 32 million bytes of
The MP3 movement is one of the most amazing phenomena that                space. That’s a lot of space for one song, and it’s especially large
the music industry has ever seen. Unlike other movements — for            when you consider that over a 56K modem, it would take close to
example, the introduction of the cassette tape or the CD — the            two hours to download that one song.
MP3 movement started not with the industry itself but with a              The MP3 format is a compression system for music. The MP3
huge audience of music lovers on the Internet. The MP3 format             format helps reduce the number of bytes in a song without
for digital music has had, and will continue to have, a huge              hurting the quality of the song’s sound. The goal of the MP3
impact on how people collect, listen to and distribute music.             format is to compress a CD-quality song by a factor of 10 to 14
                                                                          without noticably affecting the CD-quality sound. With MP3, a
                                                                          32-megabyte (MB) song on a CD compresses down to about 3
                                                                          MB. This lets you download a song in minutes rather than hours,
                                                                          and store hundreds of songs on your computer’s hard disk
                                                                          without taking up that much space.

                                                                          Is it possible to compress a song without hurting its quality? We
                                                                          use compression algorithms for images all the time. For example, a
                                                                          GIF file is a compressed image. So is a JPG file. We create Zip files
                                                                          to compress text. So we are familiar with compression algorithms
If you have ever wondered how MP3 files work, or if you have              for images and words and we know they work. To make a good
heard about MP3 files and wondered how to use them yourself,              compression algorithm for sound, a technique called perceptual
then this article is for you! In this article, you will learn about the   noise shaping is used. It is “perceptual” partly because the MP3
MP3 file format and how you can start downloading, listening to           format uses characteristics of the human ear to design the
and saving MP3 files onto CDs!                                            compression algorithm. For example:
                      The MP3 Format                                      * There are certain sounds that the human ear cannot hear.
                                                                          * There are certain sounds that the human ear hears much better
If you have read How CDs Work, then you know something                      than others.
about how CDs store music. A CD stores a song as digital                  * If there are two sounds playing simultaneously, we hear the
information. The data on a CD uses an uncompressed, high-                   louder one but cannot hear the softer one.
resolution format. Here’s what happens when a CD is created:
                                                                          Using facts like these, certain parts of a song can be eliminated
* Music is sampled 44,100 times per second. The samples are 2             without significantly hurting the quality of the song for the
  bytes (16 bits) long.                                                   listener. Compressing the rest of the song with well-known
* Separate samples are taken for the left and right speakers in a         compression techniques shrinks the song considerably — by a
  stereo system.                                                          factor of 10 at least. (If you would like to learn more about the
So a CD stores a huge number of bits for each second of music:            specific compression algorithms, see the links at the end this
                                                                          article.) When you are done creating an MP3 file, what you have
44,100 samples/second * 16 bits/sample * 2 channels                       is a “near CD quality” song. The MP3 version of the song does
= 1,411,200 bits per second                                               not sound exactly the same as the original CD song because
                                                                          some of it has been removed, but it’s very close.
                                                               Page 101
From this description, you can see that MP3 is nothing magical.         is a computer with a sound card and speakers and an Internet
It is simply a file format that compresses a song into a smaller size   connection - things you probably already have!
so it is easier to move around on the Internet and store.
                                                                        Let’s look at many of the different things you can do with MP3
                           The Name                                     files and the software that makes it possible.
MPEG is the acronym for Moving Picture Experts Group. This                             Downloading and Listening
group has developed compression systems used for video data.
                                                                        If you would like to download and then listen to MP3 files on
For example, DVD movies, HDTV broadcasts and DSS satellite
                                                                        your computer, then you need:
systems use MPEG compression to fit video and movie data into
smaller spaces. The MPEG compression system includes a                  * A computer
subsystem to compress sound, called MPEG audio Layer-3. We              * A sound card and speakers for the computer (If your computer
know it by its abbreviation, MP3.                                         has speakers, it has a sound card.)
                                                                        * An Internet connection (If you are browsing the Web to read
                 Using the MP3 Format                                     this article, then you have an Internet connection and it is
                                                                          working fine.)
Knowing about the MP3 format isn’t half as interesting as using         * An MP3 player (a software application you can download from
it. The MP3 movement - consisting of the MP3 format and the               the Web in 10 minutes)
Web’s ability to advertise and distribute MP3 files - has done
                                                                        If you have recently purchased a new computer, chances are it
several things for music:
                                                                        already has software that can play MP3 files installed on its hard
* It has made it easy for anyone to distribute music at nearly no       disk. The easiest way to find out if you already have an MP3
  cost (or for free).                                                   player installed is to download an MP3 file and try to double-
* It has made it easy for anyone to find music and access it            click on it. If it plays, you are set. If not, you need to download a
   instantly.                                                           player, which is very easy to do.
* It has taught people a great deal about manipulating sound on
  a computer.                                                           There are literally thousands of sites on the Web where you can
                                                                        download MP3 files. (Click here to do a search for MP3 download
                                                                        sites.) Go to one of these sites, find a song and download it to
                                                                        your hard disk (most MP3 sites let you either listen to the song
                                                                        as a streaming file or download it — you want to download).
                                                                        Most songs range between 2 and 4 MB, so it will take 10 to 15
                                                                        minutes unless you have a high-speed Internet connection. Once
                                                                        the song has finished downloading, try to double-click on the file
                                                                        and see what happens. If your computer plays it, then you are
Technology has made it easier to download and play your
favorite music.
That third one was accidental but important. A big part of the
MP3 movement is the fact that it has brought an incredible array
of powerful tools to desktop computers and given people a
reason to learn how they work. Because of these tools, it is now
extremely easy for you to:
* Download an MP3 file from a Web site and play it
* Rip a song from a music CD and play it directly or encode it as
  an MP3 file
* Record a song yourself, convert it to an MP3 file and make it
  available to the world
* Convert MP3 files into CD files and create your own audio CDs
  from MP3 files on the Web
* Rip songs off of various music CDs and recombine them into
  your own custom CDs
* Store hundreds of MP3 files on data CDs
* Load MP3 files into tiny portable players and listen to them
  wherever you go
To do all of these amazing things, all you need is a computer with
a sound card and speakers, an Internet connection, a CD-R drive
to create CDs and an MP3 player. If you simply want to down-
load MP3 files from the Web and listen to them, then all you need
                                                              Page 102
If you find that you cannot play it, then you need to download
an MP3 player. There are dozens of players available, and most of       Good Boot Guide to Your MP3 Player
them are free or shareware (shareware is extremely inexpensive).
One of the most popular is WinAmp, which you can download
                                                                       With the MP3 format taking the prize for convenience and
from www.winamp.com. For a complete list of all of the top digital
                                                                       compression when it comes to music, MP3 players are now a
music downloads, check out this page from CNet.com. Once you
                                                                       portable-entertainment staple. They let you carry hours of music
download and install a player, double-click on the MP3 file that
                                                                       everywhere you go.
you downloaded and it will play.

You are now ready to begin collecting MP3 files and saving them
on your computer. Many people have hundreds of songs they
have collected, and they create jukebox-like playlists so that their
computer can play them all day long!
              Taking the Files With You
Many people who start collecting MP3 files find that they want
to listen to them in all kinds of places. Small, portable MP3
players answer this need. These players are like portable cassette
players except that they are smaller.                                                   Apple iPod 30GB MP3 player
These players plug into your computer’s parallel, FireWire or          In this article, you will learn about the technology of MP3
USB port to transfer the data, and a software application lets you     players, the different ways you can use this device, and the
transfer your MP3s into the player by simply dragging the files.       various functions you can find on MP3 player models so you’ll
Creating Your Own                                                      know what to look for if you’re in the market to buy one.

If you have a CD collection and would like to convert songs from                           The MP3 Format
your CDs into MP3 files, you can use ripper and encoder                                           MP3 Fact
software to do just that. A ripper copies the song’s file from the
CD onto your hard disk. The encoder compresses the song into           A German company, Fraunhofer Gesellschaft, originally devel-
the MP3 format. By encoding songs, you can play them on your           oped the algorithm used in MP3 in 1987. They patented the
computer or take them with you on your MP3 player.                     technology in Germany in 1989, and in the United States in 1996.

                  Writing MP3s to CDs                                  The MP3 format has completely rewritten the rules of music
                                                                       distribution. And with the growing popularity of MP3 players, it
If you have a writable CD drive in your computer, there are two        is moving beyond the computer.
ways to save your MP3 files on a CD:
                                                                       MPEG is the acronym for Moving Picture Experts Group. This
You can write the MP3 files themselves onto a data CD in order         group has developed compression systems used for video data.
to save them and clear some space on your hard disk. You can           For example, DVD movies, HDTV broadcasts and DSS satellite
then listen to the files on any computer. Some car stereos and         systems use MPEG compression to fit video and movie data into
DVD players now let you play data-encoded MP3s, too.                   smaller spaces. The MPEG compression system includes a
You can convert (decode) your MP3 files into full-size CD tracks       subsystem to compress sound, called MPEG Audio Layer-3. We
and then save them to an audio CD. This allows you to listen to        know it by its abbreviation, MP3.
your MP3 files on any CD player.                                       The MP3 format is a compression system for music. This format
WinAmp has a plug-in that creates full-size WAV files from MP3         helps to reduce the number of bytes in a song, without hurting
files, and some of the encoders will also decode. Once you have        the quality of the song’s sound. The goal of the MP3 format is to
the full-size CD tracks, then the software that comes with your        compress a CD-quality song by a factor of 10 to 14, without
CD-R drive will let you create an audio CD easily.                     losing the CD sound quality. A 32-megabyte (MB) song on a CD
                                                                       compresses down to about 3 MB on MP3. This lets you down-
                                                            Page 103
load a song in minutes rather than hours, and you can store 10 to                               MP3 Fact
20 songs on an MP3 player using a relatively small amount of
                                                                     MP3 format was originally intended to be used for HDTV
For more information on MP3 files and file sizes, see:
                                                                                    Parts of an MP3 Player
* How MP3 Files Work - details on the compression process
* How Analog and Digital Recording Works - details on turning        Let’s take a look at the components that make up a typical MP3
  sound into bytes                                                   player:
* How CDs Work                                                       * Data port * Memory * Microprocessor * Display * Amplifier
In the next section, you’ll learn how to combine the MP3 format      * Digital signal processor (DSP) * Playback controls
with the MP3 player.                                                 * Audio port * Power supply

           Taking Your MP3 Files with You                            The player plugs into your computer’s USB port, FireWire port or
                                                                     parallel port to transfer data. USB-based players transfer data
Many people who start collecting MP3 files find that they want       many times faster than those that use the parallel port. The MP3
to listen to them in all kinds of places. Small, portable MP3        files are saved in the player’s memory.
players answer this demand. These players are like portable
                                                                     Memory types include:
cassette or CD players, except that they are smaller and they use
solid state memory instead of a physical medium like a tape or a     * Internal Flash memory * CompactFlash cards * Memory Stick
CD. All of the players currently on the market include a software    * SmartMedia cards * Internal microdrive
application that lets you transfer your MP3 files into the player.   With the exception of the last one, these are all types of solid
Most of them also include utilities for copying music from CDs or    state memory. The advantage to solid state memory is that there
Web sites, and the ability to create custom playlists.               are no moving parts; and no moving parts means better reliability
                                                                     and no skips in the music.
                                                                     The inside of a Rio MP3 player. You can see the LCD panel,
                                                                     several large chips (the microprocessor, DSP chip and I/O
                                                                     controller), the amplifier and the buttons.

The MP3 player is a wonderful example of a new use of existing
technologies. None of the components in a typical MP3 player is
radical, or even new, technology. By simply combining these
components in a new way, and writing some code to control it all,
manufacturers have created an entirely new line of consumer
The job of the MP3 player is pretty straightforward. When you
play a song, the player must:
1. Pull the song from memory byte by byte
2. Decompress the MP3 encoding
3. Run the decompressed bytes through a digital-to-analog
4. Amplify the analog signal so you can hear it
The main difference between a portable CD player and an MP3
player is that the CD contains the bytes instead of memory, and
on a CD the bytes are already decompressed so no decompres-
sion is needed.
                       Multiple Formats
Most MP3 players now play other formats as well, including           The microprocessor is the brains of the player. It monitors user
WMA, WAV, MIDI, AAC, Ogg Vorbis and Audible (an audio-               input through the playback controls, displays information about
book sound format). To learn more about these and other audio        the current song on the LCD panel and sends directions to the
formats, see The MP3 and Internet Audio Handbook: Digital            DSP chip that tells it exactly how to process the audio.
Audio Formats and CDBurner.ca: Compare Digital Audio For-
mats!.                                                               The DSP pulls the song data from memory, applies any special
                                                                     effects, or EQ, and streams it to the amplifier. The DSP runs a
                                                         Page 104
decompression algorithm that undoes the compression of the      What Can You Do with an MP3 Player?
MP3 file and then a digital-to-analog converter turns the bytes
back into waves                                                       With a portable MP3 player, a personal computer, and the
                                                                      appropriate software, you can do the following:
The amplifier boosts the strength of the signal and sends it to the   * Obtain free or low-cost music from the Web
audio port, where a pair of headphones or ear buds are con-           * Create your own mix of music (download MP3 files from
nected.                                                                 Web, convert tracks from CDs)
                                                                      * Listen to near-CD quality music wherever you go
                                                                      * Listen to more music (up to 10 hours’ worth)
                                                                      The easiest way to obtain songs in MP3 format is to find them on
                                                                      the Web. See How MP3 Files Work for details on downloading
                                                                      and listening to MP3 files.
                                                                      In the next section, we’ll talk about the process of ripping songs
                                                                      from your CDs and downloading them into the player.
                                                                               Converting and Downloading Files
                                                                      If you have a CD collection, and would like to convert songs
                                                                      from your CDs into MP3 files, you can use ripper and encoder
                       Playing MP3 files                              software. A ripper copies a song’s file from the CD onto your
                                                                      hard disk. The encoder compresses the song into the MP3
                                                                      format. By encoding songs, you can play them on your computer
All of the portable MP3 players are battery-powered. Most use         or take them with you on your MP3 player. The ripper and
one or two AA batteries and last for approximately 10 to 12 hours     encoder software may come with your MP3 player.
on a single charge. Many of the players also have AC adapters
                                                                      The specific instructions will vary with the individual software
so they can be plugged into a normal electrical outlet, and some
                                                                      programs, but the following steps will definitely take place:
even offer DC adapters for use in a car.
                                                                      * Place the CD from which you want to convert songs into your
MP3 players that contain tiny hard disk drives can store 10 to 150      drive.
times more than Flash memory devices can.                             * Select the track(s) that you want to convert to MP3 format.
                 MP3 Player Functions                                 * Convert the selected track(s).
                                                                      * Copy the new MP3 files on to your computer’s hard disk.
                           MP3 Fact
                                                                      Now you are ready to download these MP3 files into your
MP3 is actually part of the video format MPEG-2. There is no          portable MP3 player.
MPEG-3. The key features of the planned MPEG-3 format were
integrated into MPEG-2. The next generation will be MPEG-4.              Downloading MP3 Files to an MP3 Player
The MP3 format is a compression system for digital music that         Once you have MP3 files on your computer, you can use the
helps reduce the size of a digitized song without hurting the         software that came with your MP3 player to download the files
sound quality. Digital music is converted to MP3 format and           into your MP3 player. Again, the specific instructions will vary
made available for individual use, usually on the Web. You can        depending upon your software program and player, but you will:
download MP3 files from the Internet using your computer and          * Create a playlist from your MP3 files.
special software, either commercial or freeware. You can also         * Plug the player into your computer’s parallel or USB port
convert digital music from a CD into MP3 format using your              (depending on the features of your player).
computer and commercial or free software.                             * Transfer the MP3 files according to the instructions.
You can play MP3 files in three different ways:                       The process only takes a few minutes!
* You can play them directly on a personal computer                                     Using an MP3 Player
* You can decompress an MP3 file and record it onto a CD
* You can play MP3 files on a portable MP3 player. (Note: here        Once you have downloaded the MP3 files into your portable
  we are referring to “MP3 player” as the device, rather than the     MP3 player, you are ready to take your music anywhere. Most
  software used to play the MP3 file on a desktop or laptop           MP3 players are small (3 in x 5 in / 7.5 cm x 11.5 cm, or less),
  computer.)                                                          lightweight, and solid-state. Because most players are solid-state,
                                                                      there are no moving parts to break down or skip, so the sound
The advantage of MP3 players is that they are small, lightweight
                                                                      quality is uninterrupted regardless of your physical activity. MP3
and rugged. They are a great way to carry your MP3 files with
                                                                      players are equipped with various types of headphones or
                                                                Page 105
Portable MP3 players can play music longer than a portable CD                                       FAQ
player. The length of play for a CD player is about 74 minutes, the
length of one CD. However, the length of play for an MP3 player                               What is MP3?
depends upon its memory capacity, which can be upgraded on
                                                                      The MP3 format is a compression system for music. The MP3
some models. A standard MP3 player can play for about half an
                                                                      format helps to reduce the number of bytes in a song without
hour (32 MB) to a few weeks (40 GB)! Some models can be
                                                                      hurting the sound quality. The goal of the MP3 format is to
upgraded with additional memory devices.
                                                                      compress a CD-quality song by a factor of 10 to 14, without
Next, we’ll talk about some other features you can find in MP3        losing the CD quality of the sound. A 32-megabyte song on a CD
players.                                                              compresses down to 3 megabytes or so on MP3. This lets you
                                                                      download a song in minutes rather than hours, and store
                           Features                                   hundreds of songs on your computer’s hard disk without taking
When you’re picking out your MP3 player, you should pay               up that much space.
attention to the following features (in addition to the usual         Is the sound quality of MP3 better than a CD?
considerations like size, weight, durability, price, etc.):
                                                                      No. Because MP3 is a compression format, it throws away some
* Type of connection (USB, FireWire or parallel)
                                                                      of the information from a CD format. MP3 format uses character-
* Memory amount
                                                                      istics of the human ear to design the compression algorithm. For
* Memory type
* Operating system support - Make sure the player supports the
  operating system you have on your computer, or else you             * There are certain sounds that the human ear cannot hear.
  won’t be able to do much with it.                                   * There are certain sounds that the human ear hears much better
                                                                        than others.
                           Memory                                     * If there are two sounds playing simultaneously, we can only
                                                                        hear the louder one.
                           MP3 Fact
                                                                      Using such facts about the human ear, certain parts of a song can
An average CD song, three minutes long, takes up 32 MB of
                                                                      be eliminated without significantly hurting the quality of the
space. A three-minute MP3 song takes up about 1.6 MB, which
                                                                      song for the listener. Compressing the rest of the song using
means that approximately 20 MP3 songs can fit into the same
                                                                      well-known compression techniques shrinks the song consider-
space as one CD song.
                                                                      ably - by a factor of 10 at least. When you are done creating an
                                                                      MP3 file, what you have is “near-CD” quality. The MP3 version
The MP3 files are saved in the player’s memory. Most models are
                                                                      of the song will not sound exactly the same as the original CD,
equipped with anywhere from 32 megabytes (MB) to 60
                                                                      because some of the song has been removed, but it will be very
gigabytes (GB). Memory can be upgraded in some models. The
type of memory in MP3 players is either totally internal, totally
removable, or some combination of the two (optional on some                         Where can I find MP3 files
models). Memory types include:                                                         for my MP3 player?
* Internal Flash memory * CompactFlash cards * Memory Stick
                                                                      All that you need to do is type “MP3” into any search engine
* SmartMedia cards * Internal microdrive
                                                                      and you will find that there are literally thousands of sites on the
With the exception of the last one, these are all types of solid      Web where you can download MP3 files. Click here to do a
state memory. The advantage to solid state memory is that there       search.
are no moving parts, and no moving parts means no skips in the
                                                                      Some music sites and MP3 players are now partnering up to offer
music and better reliability.
                                                                      player-specific synchronization services. For instance, the Apple
The advantage of the MP3 players equipped with a microdrive is        iPod is tied in with Apple’s online music store, iTunes, and
a huge song capacity. A microdrive is basically a miniature hard      Samsung’s (the Napster Player) is partnered up with Napster.com.
disk, like you find in a desktop or laptop computer. A hard disk
                                                                                   Can I record music from CDs
can have anywhere from 300 megabytes to 60 gigabytes of space
- enough to hold weeks of music!                                                       for my MP3 Player?

         USB, FireWire and Parallel Port                              Yes, if you have a CD collection and would like to convert songs
                                                                      from your CDs into MP3 files, you can use ripper and encoder
If your computer is equipped with USB ports, then you definitely      software to convert your favorite songs. A ripper copies the
want to buy a USB player. A high-speed USB connection is the          song’s file from the CD onto your hard disk. The encoder
fastest option. Here is the transfer-speed breakdown:                 compresses the song into the MP3 format. By encoding songs
* USB 2.0 (high-speed USB): up to 480 Mbps                            you can play them on your computer or take them with you on
* FireWire: up to 400 Mbps                                            your MP3 player. The ripper and encoder software may come
* USB 1.0: up to 12 Mbps                                              with your MP3 player.
* Parallel (standard): up to 115 KBps
                                                                Page 106
To convert your CD songs into MP3 format, you will need:                 Given that it was distributing an illegal product, the original
* a computer                                                             Napster’s key weakness lay in its architecture - the way that the
* a CD-ROM, DVD-ROM, CD-R, or CD-RW drive (internal or                   creators designed the system. When the courts decided that
 external)                                                               Napster was promoting copyright infringement, it was very easy
* ripper/encoder software                                                for a court order to shut the site down.
The specific instructions will vary with the individual software         The fact that Napster promoted copyright violations did not
programs, but the following steps will definitely take place:            matter to its users. Most of them have turned to a new file-
* Place the CD from which you want to convert songs into your            sharing architecture known as Gnutella. In this article, you will
  drive.                                                                 learn about the differences between Gnutella and the old Napster
* Select the track(s) that you want to convert to MP3 format.            that allow Gnutella to survive today despite a hostile legal
* Convert the selected track(s).                                         environment.
* Copy the new MP3 files onto your computer’s hard disk.                                       The New Napster
Now, you are ready to download these files into your portable            Napster was relaunched by new parent company Roxio in 2003. It
MP3 player.                                                              is now a legal, pay-for-music site — no copyright infringement in
                  Can I record music                                     Napster version 2.
             from my MP3 player to a CD?
                                                                                         Napster’s Architecture
Yes, if you have a writable CD drive in your computer, you can
convert (decode) your MP3 files into full-size CD tracks, and then       On the Web as it is normally implemented, there are Web servers
save them to an audio CD. This allows you to listen to your              that hold information and process requests for that information
favorite MP3 files on any CD player.                                     (see How Web Servers Work for details). Web browsers allow
                                                                         individual users to connect to the servers and view the informa-
WinAmp has a plug-in that will create full-size WAV files from an        tion. Big sites with lots of traffic may have to buy and support
MP3 file, and some of the encoders will also decode. Once you            hundreds of machines to support all of the requests from users.
have the full-size CD tracks, the software that comes with your
CD-R drive will let you create an audio CD easily.
                                                                         Napster pioneered the concept of peer-to-peer file sharing.
                         Is MP3 legal?
                                                                         With the old version of Napster (Napster relaunched itself in 2003
Yes, MP3 is merely a data compression format. However, what              as a legal, pay-for-music site), individual people stored files that
you do with that format can be legal or illegal. The distribution of     they wanted to share (typically MP3 music files) on their hard
music in MP3 format over the Internet has prompted much legal            disks and shared them directly with other people. Users ran a
debate and action over copyright law. In fact, the Recording             piece of Napster software that made this sharing possible. Each
Industry Association of America won a suit against the original          user machine became a mini server.
Napster over illegal distributions of MP3 files. (Napster is now
back online as a legal pay-for-music service.)
                  What is sampling rate?
Sampling rate refers to how often samples are taken from the
original music signal. The higher the sampling rate, the better the
sound quality, or fidelity; however, the higher the sampling rate,
the more storage space is needed for the file.

     Good Boot Guide to File Sharing
At its peak, Napster was perhaps the most popular Web site ever
created. In less than a year, it went from zero to 60 million visitors
per month. Then it was shut down by a court order because of
copyright violations, and wouldn’t relaunch until 2003 as a legal
music-download site.
The original Napster became so popular so quickly because it
offered a unique product — free music that you could obtain
nearly effortlessly from a gigantic database. You no longer had to
go to the music store to get music. You no longer had to pay for
it. You no longer had to worry about cueing up a CD and finding
a cassette to record it onto. And nearly every song in the
universe was available.
                                                              Page 107
If you logged into the old Napster to download a song, here’s          * There are many different client applications available to access
what happened:                                                          the Gnutella network.
1. You started the Napster software on your machine. Your              Because of both of these features, it would be difficult for a
  machine became a small server able to make files available to        simple court order to shut Gnutella down. The court would have
    other Napster users.                                               to find a way to block all Gnutella network traffic at the ISP and
2. Your machine connected to Napster’s central servers. It told        the backbone levels of the Internet to stop people from sharing.
   the central servers which files were available on your machine.
   So the Napster central servers had a complete list of every                               Gnutella Clients
    shared song available on every hard disk connected to Napster
                                                                       The original Napster had one piece of “client software” - the
   at that time.
                                                                       software that users ran on their machines to access the Napster
3. You typed in a query for a song. Let’s say you were looking for
                                                                       servers. Gnutella has dozens of clients available. Some of the
   the song “Roxanne” by The Police. Napster’s central servers
                                                                       popular Gnutella clients include:
   listed all of the machines storing that song.
4. You picked a version of the song from the list.                     * BearShare * Gnucleus * LimeWire * Morpheus * WinMX
5. Your machine connected to the user’s machine that had that          * XoloX
   song, and downloaded the song directly from that machine.                   How a Gnutella client finds a song
The creator of Napster had a couple of reasons for this approach:      Given that there is no central server to store the names and
* Napster eventually grew to have billions of songs available.         locations of all the available files, how does the Gnutella software
  There is no way a central server could have had enough disk          on your machine find a song on someone else’s machine? The
  space to hold all the songs, or enough bandwidth to handle all       process goes something like this:
   the requests.                                                       * You type in the name of the song or file you want to find.
* Napster was trying to take advantage of a loophole in copy           * Your machine knows of at least one other Gnutella machine
  right law that allows friends to share music with friends. The         somewhere on the network. It knows this because you’ve told
  legal concept behind Napster was, “All of these people are             it the location of the machine by typing in the IP address, or
  sharing the songs on their hard disks with their friends.” The         because the software has an IP address for a Gnutella host pre-
  courts did not agree with that logic, but it gave Napster enough       programmed in. Your machine sends the song name you typed
  time to prove the concept and grow to massive size.                    in to the Gnutella machine(s) it knows about.
This approach worked great and made fantastic use of the               * These machines search to see if the requested file is on the
Internet’s architecture. By spreading the load for file download-        local hard disk. If so, they send back the file name (and machine
ing across millions of machines, Napster accomplished what               IP address) to the requester.
would have been impossible any other way.                              * At the same time, all of these machines send out the same
                                                                          request to the machines they are connected to, and the process
The central database for song titles was Napster’s Achilles’ heel.       repeats.
When the court ordered Napster to stop the music, the absence          * A request has a TTL (time to live) limit placed on it. A request
of a central database killed the entire original Napster network.        might go out six or seven levels deep before it stops propagat-
With the original Napster gone, what you had at that point was           ing. If each machine on the Gnutella network knows of just four
something like 100 million people around the world hungry to             others, that means that your request might reach 8,000 or so
share more and more files. It was only a matter of time before           other machines on the Gnutella network if it propagates seven
another system came along to fill the gap.                               levels deep.

                Gnutella’s Architecture                                It is an extremely simple and clever way of distributing a query to
                                                                       thousands of machines very quickly.
Currently, the most popular system for sharing files is another
peer-to-peer network called Gnutella, or the Gnutella network.
There are two main similarities between Gnutella and the old
* Users place the files they want to share on their hard disks and
  make them available to everyone else for downloading in peer-
  to-peer fashion.
* Users run a piece of Gnutella software to connect to the
 Gnutella network.
There are also two big differences between Gnutella and the old
* There is no central database that knows all of the files available
  on the Gnutella network. Instead, all of the machines on the
  network tell each other about available files using a distributed
  query approach.
                                                                Page 108
This approach has one big advantage - Gnutella works all the                         XoloX Example: Downloading
time. As long as you can get to at least one other machine
running Gnutella software, you are able to query the network. No         To download a file, you simply double-click it in the search
court order is going to shut this system down, because there is          window. This sends the file name to the Transfer window. Once a
no one machine that controls everything. However, Gnutella has           filename is in the transfer window, your copy of XoloX will
at least three disadvantages:                                            connect to the peer machine to download the file. One nice thing
                                                                         about XoloX/Gnutella is that if multiple machines have the file
* There is no guarantee that the file you want is on any of the
                                                                         available, your client can connect to several of them simulta-
  8,000 machines you can reach.
                                                                         neously to download the file very quickly. In the figure below,
* Queries for files can take some time to get a complete response.
                                                                         you can see that Filename1.avi in particular is taking advantage
  It might be a minute or more before all of the responses, seven
                                                                         of this capability to download the file at a rate of 69.2 kilobytes
  levels deep, come in.
                                                                         per second. XoloX is estimating 43 minutes to complete the
* Your machine is part of this network. It is answering requests
                                                                         download of over 100 megabytes.
   and passing them along, and in the process routing back
  responses as well. You give up some amount of your band-
  width to handle requests from all the other users.
Apparently, these disadvantages are minor, because people have
                                                                         When you pick a file for downloading, it is fairly common for
downloaded hundreds of millions of copies of Gnutella clients.
                                                                         nothing to happen. That is, XoloX cannot connect to the
               XoloX Example: Searching                                  machine that has the file, or the machine holding the file is
                                                                         already busy helping other people. You can solve this problem
XoloX is a typical, fairly simple program for connecting into the        either by waiting (eventually a busy machine can get unbusy), by
Gnutella network. It does not have some of the bells and whistles        choosing files with high scores (increasing the likelihood of
of the more sophisticated clients, but it does work, it is a small       finding an unbusy machine), or by deleting a file that is going
file to download (only 600 kilobytes or so), it has no “spyware”         nowhere from the transfer window and replacing it with an
or bundled pop-up advertising mixed in with it, and it is very easy      identical file from the search window.
to install and use. Its simplicity makes it useful to demonstrate
how a typical Gnutella client works.                                     Once you have the files on your machine, you can find them in a
                                                                         XoloX directory and in the Files window of XoloX. You can share
                                                                         all the files you’ve downloaded with other people if you like. You
                                                                         do this by first specifying the directories and file types you want
                                                                         to share in the Preferences dialog:

There are three big things you can do with XoloX: search for
files, transfer files to your machine and look at your downloaded
files. There are three buttons at the top of the XoloX window that
let you toggle between these three activities.
The figure above shows a typical screenshot during a search. All
you do is type in the name (or keywords) of the file you are
looking for. You can also select the file type: audio, video, etc., or
“All Types.” Your XoloX client sends out a message containing
your search string, and over the course of 30 to 60 seconds a
search window fills with results from the thousands of other
machines that are processing your query.
One thing you will notice in the search window is a score. The
score represents the number of machines currently online that
have the same file available. By choosing a file with a high score,
you increase your odds of actually getting the file you want.
                                                                 Page 109
You can also control how much outgoing bandwidth you allow              But the other function of a surge protector power strip -
XoloX to consume when people download files from you:                   protecting the electronics in your computer from surges in
                                                                        power - is far more important. So let’s take a look at
                                                                        surge protectors, also called surge suppressors, to find out
                                                                        what they do, when you need them, and how well they
                                                                        work. We’ll also find out what levels of protection are
                                                                        available and see why you might not have all the protection
                                                                        you need, even if you do use a quality surge protector.

                                                                                                 Surge Basics
                                                                        The main job of a surge protector system is to protect electronic
                                                                        devices from “surges.” So if you’re wondering what a surge
                                                                        protector does, the first question is, “What are surges?” And
                                                                        then, “Why do electronics need to be protected from them?”
                                                                        A power surge, or transient voltage, is an increase in voltage
                                                                        significantly above the designated level in a flow of electricity. In
                                                                        normal household and office wiring in the United States, the
                                                                        standard voltage is 120 volts. If the voltage rises above 120 volts,
                                                                        there is a problem, and a surge protector helps to prevent that
                                                                        problem from destroying your computer.
                                                                        To understand the problem, it is helpful to understand something
                                                                        about voltage. Voltage is a measure of a difference in electric
                                                                        potential energy. Electric current travels from point to point
                                                                        because there is a greater electric potential energy on one end of
This can keep people from chewing up all your upstream band-            the wire than there is on the other end. This is the same sort of
width.                                                                  principle that makes water under pressure flow out of a hose —
                     Is Gnutella Legal?                                 higher pressure on one end of the hose pushes water toward an
                                                                        area of lower pressure. You can think of voltage as a measure of
Gnutella itself is legal. There is no law against sharing public        electrical pressure.
domain files. It’s when people use Gnutella to distribute copy-
                                                                        As we’ll see later on, various factors can cause a brief increase in
righted music and films that its use becomes illegal. This is the
problem that got Napster in trouble. The music industry is
officially upset about Gnutella, but there is currently no easy way     * When the increase lasts three nanoseconds (billionths of a
to control it.                                                            second) or more, it’s called a surge.
                                                                        * When it only lasts for one or two nanoseconds, it’s called a
Attacking the Gnutella architecture is one way to disrupt file-           spike.
sharing activities. There are currently two approaches being
                                                                        If the surge or spike is high enough, it can inflict some heavy
                                                                        damage on a machine. The effect is very similar to applying too
1. Overloading the Gnutella network with a flood of bogus search        much water pressure to a hose. If there is too much water pres-
   packets.                                                             sure, a hose will burst. Approximately the same thing happens
2. Filling Gnutella servers with corrupted files.                       when too much electrical pressure runs through a wire — the wire
Gnutella’s many developers have adapted to problems in the              “bursts.” Actually, it heats up like the filament in a light bulb and
past, so it is probable that new software can work around these         burns, but it’s the same idea. Even if increased voltage doesn’t
threats and keep the files flowing.                                     immediately break your machine, it may put extra strain on the
                                                                        components, wearing them down over time. In the next section,
The debate at the moment is how much financial damage file-
                                                                        we’ll look at what surge protectors do to prevent this from
sharing actually causes. Is a shared file a theft, or is it a form of
free advertising and exposure just like airtime on the radio is?
                                                                                      The Process of Protection
            Good Boot Guide to Your                                     A standard surge protector passes the electrical current along
                Surge Protector                                         from the outlet to a number of electrical and electronic devices
                                                                        plugged into the power strip. If the voltage from the outlet surges
When you put together a computer system, one piece of standard          or spikes - rises above the accepted level - the surge protector
equipment you should buy particularly if you live in SWF is a           diverts the extra electricity into the outlet’s grounding wire.
surge protector. Most designs serve one immediately obvious             In the most common type of surge protector, a component called a
function - they let you plug multiple components into one power         metal oxide varistor, or MOV, diverts the extra voltage. As you
outlet. With all of the different components that make up a             can see in the diagram below, an MOV forms a connection
computer system, this is definitely a useful device.                    between the hot power line and the grounding line.
                                                               Page 110
An MOV has three parts: a piece of metal oxide material in the          When the voltage is at a certain level, the makeup of the gas is
middle, joined to the power and grounding line by two semicon-          such that it is a poor conductor. When the voltage surges above
ductors.                                                                that level, the electrical power is strong enough to ionize the gas,
                                                                        making it a very effective conductor. It passes on current to the
                                                                        ground line until the voltage reaches normal levels, and then
                                                                        becomes a poor conductor again.
                                                                        Both of these methods have a parallel circuit design — the extra
                                                                        voltage is fed away from the standard path to another circuit. A
                                                                        few surge protector products suppress surges with a series circuit
                                                                        design — the extra electricity isn’t shunted to another line, but
                                                                        instead is slowed on its way through the hot line. Basically, these
                                                                        suppressors detect when there is high voltage and then store the
                                                                        electricity, releasing it gradually. The companies that make this
                                                                        type of protector argue that the method offers better protection
                                                                        because it reacts more quickly and doesn’t dump electricity in the
                                                                        ground line, possibly disrupting the building’s electrical system.
                                                                        As a backup, some surge protectors also have a built-in fuse. A
                                                                        fuse is a resistor that can easily conduct current as long as the
                                                                        current is below a certain level. If the current increases above the
                                                                        acceptable level, the heat caused by the resistance burns the fuse,
                                                                        thereby cutting off the circuit. If the MOV doesn’t stop the power
                                                                        surge, the extra current will burn the fuse, saving the connected
                                                                        machine. This fuse only works once, as it is destroyed in the

These semiconductors have a variable resistance that is depen-
dent on voltage. When voltage is below a certain level, the
electrons in the semiconductors flow in such a way as to create a
very high resistance. When the voltage exceeds that level, the
electrons behave differently, creating a much lower resistance.
When the voltage is correct, an MOV does nothing. When
voltage is too high, an MOV can conduct a lot of current to
eliminate the extra voltage.                                                Inside a surge protector with line-conditioning chokes
As soon as the extra current is diverted into the MOV and to            Some surge protectors have a line-conditioning system for
ground, the voltage in the hot line returns to a normal level, so the   filtering out “line noise,” smaller fluctuations in electrical current.
MOV’s resistance shoots up again. In this way, the MOV only             Basic surge protectors with line-conditioning use a fairly simple
diverts the surge current, while allowing the standard current to       system. On its way to the power strip outlet, the hot wire passes
continue powering whatever machines are connected to the surge          through a toroidal choke coil. The choke is a just ring of magnetic
protector. Metaphorically speaking, the MOV acts as a pressure-         material, wrapped with wire - a basic electromagnet. The ups and
sensitive valve that only opens when there is too much pressure.        downs of the passing current in the hot wire charge the electro-
                      Other Systems                                     magnet, causing it to emit electromagnetic forces that smooth out
                                                                        the small increases and decreases in current. This “conditioned”
Another common surge protection device is a gas discharge               current is more stable, and so easier on your computer (or other
arrestor, or gas tube. These tubes do the same job as an MOV -          electronic device).
they divert the extra current from the hot line to the ground line.
They do this by using an inert gas as the conductor between the                                 Surge Sources
two lines.                                                              Power surges occur when something boosts the electrical charge
                                                                        at some point in the power lines. This causes an increase in the
                                                              Page 111
electrical potential energy, which can increase the current flowing      the life of your computer, and it could very easily wipe out all
to your wall outlet. A number of different things can cause this to      of your saved data or destroy your system. Computers are very
happen.                                                                  expensive items, and the data they hold is often irreplaceable,
                                                                         so it’s only good economic sense to invest in a quality surge
The most familiar source is probably lightning, though it’s
actually one of the least common causes. When lightning strikes
                                                                       * It’s a good idea to use surge protectors for other high-end
near a power line, whether it’s underground, in a building or
                                                                         electronic equipment, such as entertainment center components.
running along poles, the electrical energy can boost electrical
                                                                         A surge protector will generally extend the life of these devices,
pressure by millions of volts. This causes an extremely large
                                                                         and there’s always a chance that a big power surge will causes
power surge that will overpower almost any surge protector. In a
                                                                         severe damage.
lightning storm, you should never rely on your surge protector to
save your computer. The best protection is to unplug your                                                       One problem with surge
computer.                                                                                                       protectors is that the
                                                                                                                MOVs can burn out with
A more common cause of power surges is the operation of high-
                                                                                                                one good surge. This is
power electrical devices, such as elevators, air conditioners and
                                                                                                                why it’s good to get a
refrigerators. These high-powered pieces of equipment require a
                                                                                                                protector with an
lot of energy to switch on and turn off components like compres-
                                                                                                                indicator light that tells
sors and motors. This switching creates sudden, brief demands
                                                                                                                you whether or not it’s
for power, which upset the steady voltage flow in the electrical
                                                                                                                functioning properly.
system. While these surges are nowhere near the intensity of a
lightning surge, they can be severe enough to damage compo-
nents, immediately or gradually, and they occur regularly in most
building’s electrical systems.
Other sources of power surges include faulty wiring, problems
                                                                       Even if you connect surge protectors to all of your outlets, your
with the utility company’s equipment, and downed power lines.
                                                                       equipment might be exposed to damaging surges from other
The system of transformers and lines that brings electricity from a
                                                                       sources. Telephone and cable lines can also conduct high voltage
power generator to the outlets in our homes or offices is extraordi-
                                                                       - for full protection, you should also guard against surges from
narily complex. There are dozens of possible points of failure, and
                                                                       your telephone or cable lines. Any lines carrying signals into your
many potential errors that can cause an uneven power flow. In
                                                                       home can also carry a power surge, due to lightning or a number
today’s system of electricity distribution, power surges are an
                                                                       of other factors. If your computer is connected to the phone lines
unavoidable occurrence. In the next section, we’ll see what this
                                                                       via a modem, you should get a surge protector that has a phone-
could mean to you.
                                                                       line input jack. If you have a coaxial cable line hooked up to
              Protecting Your Equipment                                expensive equipment, consider a cable surge protector. Surges on
                                                                       these lines can do just as much damage as surges over power
In the last section, we saw that power surges are a regular            lines.
occurrence, unavoidable with our current system of providing
electricity to homes and offices. This raises an interesting                         Levels of Surge Protection
question: If power surges are an inherent part of our electrical
                                                                       All surge protectors are not created equal. In fact, there is a
system, why didn’t we need surge protectors in our homes 50
                                                                       tremendous range in both performance and price of protection
years ago?
The answer is that a lot of the components in sophisticated
                                                                       * At one end, you have your basic $5 surge protector power strip,
modern electronic devices (such as computers, microwaves, DVD
                                                                        which will offer very little protection.
players) are much smaller and more delicate than components in
                                                                       * On the other end you have systems costing hundreds of
older machines, and are therefore more sensitive to current
                                                                         thousands of dollars, which will protect against pretty much
increases. Microprocessors, which are an integral part of all
                                                                         everything short of lightning striking nearby.
computers as well as many home appliances, are particularly
sensitive to surges. They only function properly when they             Most systems have limitations of some sort; picking out a
receive stable current at the right voltage.                           protector system that suits you is a matter of balancing the cost
                                                                       of the system with the cost of losing data or electronic equipment.
So whether or not you should get a surge protector depends on
                                                                       As with insurance, you find the level of coverage you’re comfort-
what sort of device you’re hooking up to the power supply.
                                                                       able with.
* There’s no reason to hook up a light bulb to a surge protector
                                                                       To protect your equipment from surges, you need individual
  because the worst that is likely to happen due to a power surge
                                                                       surge protectors for each outlet. These power strips range a great
  is that your light bulb will burn out.
                                                                       deal in quality and capacity (as we’ll see in the next section).
* You should definitely use a surge protector with your computer.
                                                                       There are three basic levels of power strip surge protectors:
  It is filled with voltage-sensitive components that a power surge
  could damage very easily. At the least, this damage will shorten
                                                                Page 112
* Basic power strip - These are basic extension cord units with          Many UL-listed products are also of inferior quality, of course,
 five or six outlets. Generally, these models provide only basic         but you’re at least guaranteed that they have some surge
  protection.                                                            protection capabilities and meet a marginal safety standard. Be
* Better power strip - For $15 to $25 you can get a power strip          sure that the product is listed as a transient voltage surge
  surge protector with better ratings and extra features, such as a      suppressor. This means that it meets the criteria for UL 1449, UL’s
  protection indicator light and individual switches for each            minimum performance standard for surge suppressors. There are a
  outlet.                                                                lot of power strips listed by UL that have no surge protection
* Surge station - These large surge protectors fit under your            components at all. They are listed only for their performance as
  computer or on the floor. They offer superior voltage protection       extension cords.
  and advanced line conditioning. Most models also have an
                                                                         On a listed surge protector, you should find a couple of ratings.
  input for a phone line, to protect your modem from power
                                                                         Look for:
  surges, and may feature built-in circuit breakers. You can get
                                                                         * Clamping voltage - This tells you what voltage will cause the
  one of these units for as little $30, or you can spend upward of
                                                                           MOVs to conduct electricity to the ground line. A lower
 $100 for a more advanced model.
                                                                           clamping voltage indicates better protection. There are three
* Uninterruptable Power Supply (UPS) - Some units combine
                                                                          levels of protection in the UL rating - 330 V, 400 V and 500 V.
  surge protection with a continuous UPS. The basic design of a
                                                                          Generally, a clamping voltage more than 400 V is too high.
  continuous UPS is to convert AC power to DC power and store
                                                                         * Energy absorption/dissipation - This rating, given in joules,
  it on a battery. The UPS then converts the battery’s DC power
                                                                           tells you how much energy the surge protector can absorb
  back to AC power and runs it to the AC outlets for your
                                                                           before it fails. A higher number indicates greater protection.
  electronics. If the power goes out, your computer will continue
                                                                           Look for a protector that is at least rated at 200 to 400 joules.
  to run, feeding off the stored battery power. This will give you a
                                                                          For better protection, look for a rating of 600 joules or more.
  few minutes to save your work and shut down your computer.
                                                                         * Response time - Surge protectors don’t kick in immediately;
  The conversion process also gets rid of most of the line noise
                                                                           there is a very slight delay as they respond to the power surge.
  coming from the AC outlet. These units tend to cost $150 or
                                                                           A longer response time tells you that your computer (or other
                                                                           equipment) will be exposed to the surge for a greater amount of
An ordinary UPS will give you a high level of protection, but you          time. Look for a surge protector that responds in less than one
should still use a surge protector. A UPS will stop most surges            nanosecond.
from reaching your computer, but it will probably suffer severe
                                                                         You should also look for a protector with an indicator light that
damage itself. It’s a good idea to use a basic surge protector, if
                                                                         tells you if the protection components are functioning. All MOVs
just to save your UPS.
                                                                         will burn out after repeated power surges, but the protector will
Once you’ve decided what level of surge protection you need, it’s        still function as a power strip. Without an indicator light, you
time to shop around for a good unit. In the next section, we’ll find     have no way of knowing if your protector is still functioning
out what you should look for when considering different models.          properly.

        Picking the Right Surge Protector                                Better surge protectors may come with some sort of guarantee of
                                                                         their performance. If you’re shopping for more expensive units,
Shopping for a surge protector is tricky business because there          look for a protector that comes with a guarantee on your com-
are a lot of nearly worthless products on the market. Research into      puter. If the unit fails to protect your computer from a power
a particular model is the best way to ensure good results, but you       surge, the company will actually replace your computer. This isn’t
can get a good idea of a product’s performance level by looking          total insurance, of course - you’ll still lose all the data on your
for a few signs of quality.                                              hard drive, which could cost you plenty - but it is a good indica-
First of all, look at price. As a general rule, don’t expect much from   tion of the manufacturer’s confidence in their product.
any surge protector that costs less than $10. These units typically      No surge protector is 100 percent effective, and even top of the
use simple, inexpensive MOVs with fairly limited capacities, and         line equipment may have some serious problems. Electronics
won’t protect your system from bigger surges or spikes.                  experts are actually somewhat divided over the best way to deal
Of course, high price doesn’t promise quality. To find out what          with power surges, and different manufacturers claim other
the unit is capable of, you need to check out its Underwriters           technologies are inherently faulty. If you’re interested in learning
Laboratories (UL) ratings. UL is an independent, not-for-profit          more about these issues, and finding out all the ways surge
company that tests electric and electronic products for safety. If a     protection technology can fail, check out some of the sites listed
protector doesn’t have a UL listing, it’s probably junk; there’s a       in the links section on the next page. Surprisingly, surge protec-
good chance it doesn’t have any protection components at all. If         tors are an extremely controversial piece of technology, and they
it does use MOVs, they may be of inferior quality. Cheaper MOVs          have sparked a great deal of debate on the Web.
can easily overheat, setting the entire surge protector on fire. This
is actually a fairly common occurrence!
                                                                Page 113

            Good Boot Guide to Your
               Home Networking
If you own multiple PCs, you have probably thought about how
great it would be if your computers could talk to each other. With
your computers connected, you could:
* Share a single printer between computers
* Share a single Internet connection among all the
  computers in your home
* Access shared files such as photographs, MP3s,
  spreadsheets and documents on any computer in the
                                                                            House Wiring Used - Existing Phone Wiring
* Play games that allow multiple users at different
* Send the output of a device like a DVD player or
  Webcam to your other computer(s)
In this article, we’ll look at all of the different methods you can
use to create a home network. Be sure to read the companion
articles about power-line networking, wireless networking and
phone-line networking. This specialized information, including
our own experiences with different networking solutions, can
help you decide which method is right for your home.
At the moment, wireless networking appears to be the easiest
and one of the least expensive options. You can buy an 802.11b            House Wiring Used - Existing Electrical Wiring
or 802.11g access point, connect it to your cable modem or DSL
modem in a few minutes, and have all your computers talking on
a network very quickly. See How WiFi Works for details.
                     Ways to Connect
You can connect your home computers in a variety of ways:
* “Officially” wire your house with data cables by hiding all the
  network cable in the walls (especially easy if you are building a
  new home)
* Run cables across the floor between computers in the same
* Install some form of wireless networking (see How WiFi
  Works for details)                                                                  House Wiring Used - None
* Link your computers through your power lines (see How
 Power-line Networking Works for details)
* Link your computers through your phone lines
* Walk diskettes and CD-Rs back and forth (which is inexpensive
  but gets to be a drag)

                                                                          House Wiring Used - Dedicated CAT-5 Wiring
                                                                      Each of these methods has advantages and disadvantages, and
                                                                      in this article we’ll discuss them in detail. But all of these
                                                                      methods (except physically carrying diskettes) require you to
                                                                      configure your computers to share printers, files and an Internet
                      House Wiring Used                               connection and to set up some level of security. This configura-
                                                               Page 114
tion process is common to any form of networking, so that’s            Each computer in your home network needs to have a different
where we’ll start. We’ll discuss how to set up sharing with            name, and they all need to be in the same workgroup.
Windows 98 and Windows XP, since they are the most common
versions of the Windows operating system used at home. The
procedure is different if you’re using another version of Win-
dows, but the basic information is still useful. For those of you
using Linux, UNIX or other operating systems, you may prefer to
skip the networking basics and go straight to Building a Network.
Once we establish a basic understanding of the configuration
process, we’ll discuss phone-line networking, power-line
networking, Ethernet networking and wireless networking in
detail. By the time you finish this series, you’ll be able to choose
the network technology that suits your needs and configure the
whole thing!
                    Networking Basics
To install a network in your home, there are three steps:
1. Choose the technology you will use for the network. The main
    technologies to choose between are standard Ethernet, phone-
   line-based, power-line-based and wireless.
2. Buy and install the hardware.
3. Configure the system and get everything talking together
Step 3 is extremely important. It is also very educational - if you
understand the configuration process, you understand every-
thing a home network is capable of doing for you.
                     Easy Networking
There are several “home-networking kits” available, and they
often include an installation CD that makes configuration very
easy. Windows XP comes with a “Network Setup Wizard” that              Here’s how you can name your PC and create a workgroup:
helps with network configuration. There are also contractors who
                                                                       1. In Windows XP, click the Start button (bottom left hand
will set up a network in your home for a fee. The software or
                                                                          corner) and select the Control Panel.
contractor will take you through each step of naming the
                                                                       2. If not already in the “Classic view”, select the Classic view
computer, sharing files, sharing printers and sharing an Internet
                                                                          option (upper left corner of the window - you can switch
                                                                          between the classic view and the category view).
However, if you have problems, or if your kit does not include a       3. Click on the “System” icon.
configuration program, you’ll need to know how to set your             4. Select the “Computer Name” tab.
network up manually. You also need to understand a manual              5. You will see that the computer has a “Full Computer Name”
setup if you plan to do-it-yourself. To assist you with setting up        and a “Workgroup”. Click the “Change” button to change
your network, we’ll discuss the following tasks, which apply no           them.
matter which networking technology you choose:                         6. In the first box, enter the name you wish to give the computer.
* Naming the PC * Sharing files * Sharing printers                        You can name it anything, but each computer in your home
* Security * Sharing an Internet connection                               must have a its own unique name.
Once you understand these tasks, you’ll understand just what           7. In the second box, enter the name you plan to use for the
your new network can do!                                                  workgroup - make sure all of the computers have the same
                                                                         workgroup name. You may want to write it down to make sure
                        Naming the PC                                     that you enter the exact same workgroup name on each
Once you have the hardware installed (discussed later in this             computer in your home network.
article), you are ready to configure your network. The first           1. In Windows 98/ME, move the mouse pointer over the
configuration step is naming the PCs in the network.Before your           Network Neighborhood icon on the desktop and click the right
computer can become part of a network, it has to have a name              mouse button once.
and a workgroup.                                                       2. Select Properties from the menu. The Network Properties
                                                                         window will pop up, listing information about the network
                                                                          adapter(s) and protocols installed on that computer.
                                                                 Page 115
3. When the window opens, click the Identification tab. You will
   see three boxes (as shown above).
4. In the first box, enter the name you wish to give the computer.
   You can name it anything, but each computer in your home
   must have a its own unique name.
5. In the second box, enter the name you plan to use for the
   workgroup - make sure all of the computers have the same
  workgroup name. You may want to write it down to make sure
   that you enter the exact same workgroup name on each
   computer in your network.
Now that we’ve got names and a workgroup, let’s move on to
file sharing.

          Networking Basics: File Sharing
One of the most common activities on any computer network is
“file sharing.” Windows makes sharing files incredibly easy, and
once you set it up, any computer on the network can share files
with any other.
                          Windows XP
Sharing a folder is extremely easy in Windows XP. Simply open
the Windows Explorer (Click the Start button, click on All
Programs, choose Accessories and click on the Windows
Explorer icon). Find the folder you wish to share. Right click on
the folder, and in the menu that appears select “Sharing and
Security...” Click on the Sharing tab. Click on “Share this folder
on the network” and give the folder a unique name.
When you share a folder, you have an option to make the folder
(and all the files in it) read-only. If it is read-only, people can look
at the files in the folder but they cannot change any of the files. If     4. Click Microsoft in that left pane. This will bring up a list of
not, then they can modify files in the folder, delete files, rename           Microsoft’s software clients in the right pane.
files and add new files. A check box lets you specify if the folder        5. Choose Client for Microsoft Networks from the list and
is read-only or not.                                                         click OK. Windows will copy all of the necessary files and
                                                                              may prompt you for the Win98 CD. If so, insert the CD and
To access a shared folder, open the Windows Explorer, Choose                  continue.
“My Network Places” in the list on the left, find the shared folder
that you wish to access and open it.                                       Once the software is installed, you should be back to the original
                                                                           Network window. Now let’s enable file sharing:
                           Windows 98
                                                                           1. Click the button labeled File and Print Sharing...
To use file sharing in Windows 98, first check that File and Printer       2. You will see two options, one for sharing files and the other
Sharing is enabled. You do this by running the mouse pointer                  for sharing printers. Click the box next to each option to
over the Network Neighborhood icon on the desktop and                         enable it.
clicking the right mouse button once. Select Properties from the           3. Once it is enabled, you will see a checkmark in the box. Click
menu. In the large white box, the item “Client for Microsoft                   OK to close the sharing-options window.
Networks” should be visible.                                               4. Click the Access Control tab near the top of the Network
Sometimes the software required to make a computer a client of a              window. For easier control of who can access which files,
particular type of network isn’t loaded. When a computer is a                 click the box beside Share-level Access Control.
“client” of a network, that computer can communicate and share             5. Click OK to close the Network window.
information with other computers that are clients of the network.          You must now select which folders you want to share. Sharing
When you first set up networking on a Windows 98/ME com-                   your entire hard drive is not recommended. It is too easy for
puter, the set-up process normally adds the “Client for Microsoft          someone to accidentally delete an important system file if the
Networks” software. Occasionally it doesn’t. If that’s the case:           whole disk is shared. Instead, create folders that will be used
1. Click Add in the Network Properties window.                             specifically to share files.
2. Choose Client from the list of choices in the window that pops
                                                                           You may want one folder for the entire family and another one
                                                                           limited to you and your spouse. Once you have identified the
3. Click Add. You will see a list of different companies or
                                                                           folder(s), move the pointer over the folder and click the right
   vendors on the left pane (side) of the window.
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mouse button to get the pop-up menu. Select the Sharing... menu
item. A window will open with several options. The default choice
for sharing is Not Shared. Change this to Shared As and type in a
name for the shared folder. The “Shared As” name does not have
to be the same as the name of the folder, but it makes it easier to
remember if it is.

                                                                          Once shared folders are set up, accessing them is simple. Double-
                                                                          click Network Neighborhood with the left mouse button to open
                                                                          up a window showing all computers in the local area network
                                                                          (LAN). Double-click the computer you wish to access. A window
                                                                          will open with a list of shared resources. Double-click the desired
                                                                          folder and a prompt will appear, asking for the password. Type in
                                                                          the password you designated for that folder, and you’re con-
                                                                          nected to that folder!
                                                                                       Networking Basics: Printers
                                                                                                   Windows XP
                                                                          Sharing a printer is extremely easy in Windows XP.
                                                                          1. In Windows XP, click the Start button (bottom left hand
                                                                             corner) and select the Control Panel.
                                                                          2. If not already in the “Classic view”, select the Classic view
   Networking Basics: File Sharing Security                                  option (upper left corner of the window - you can switch
                                                                             between the classic view and the category view).
In Windows 98 you have the option of “Share Level Access                  3. Click on the “Printers” icon.
Control”, meaning that you can password-protect shared folders.           4. Right click on the printer that you wish to share.
If you activated Share-level Access Control, you need to select           5. Click the Sharing... option.
the level of access and supply a password. Read-only access               6. Click on the sharing option and give the printer a name on the
means that anyone accessing this folder over the network can                 network.
only look at or retrieve files. They cannot put new files in the          To access a shared folder, you also use the “Printers” icon in the
folder or delete or modify existing files. Full access is just that:      control panel. Click on the “Add a Printer option. Click “Next” in
the ability to read, write, delete and create files in this folder. You   the Wizard that appears. Indicate that you wish to search for
can also choose to allow either type of access depending on               printers on the network. Then browser for the printer on the
which password is provided.                                               network and select it. You will then be able to print on the
Restricting access to certain files is crucial for most businesses        network printer as though it is connected to your own machine.
and can certainly be important to you at home. For example, you                                    Windows 98
may have documents or images that you would not want your
children to be able to see or change. Or perhaps you have                 To share a printer, first make sure you have completed the steps
important financial information that you wish to keep private.            outlined above to activate File and Printer Sharing. Then:
Whatever the reason, it is useful to be able to restrict access to        1. Click the Start button, move to Settings and select Printers. A
information on each computer through the use of share-level                 window will open listing all of the printers on the local system.
password protection. Also, you can implement the user log-on              2. Move over the icon for the printer you wish to share and click
feature by creating individual user accounts in the Users                    the right mouse button to bring up the menu. Select Sharing...
window, which is in the Control Panel.                                    3. The Properties window will pop up with the Sharing tab
                                                                             section open. Click the Shared As option and type in a name
                                                                Page 117
   for the printer. You may also elect to require a password to                                  Windows XP
   access the printer.                                                  1. In Windows XP, click the Start button (bottom left hand
4. Click OK to close the window. This printer is now shared.               corner) and select the Control Panel.
                                                                        2. If not already in the “Classic view”, select the Classic view
                                                                           option (upper left corner of the window - you can switch
                                                                           between the classic view and the category view).
                                                                        3. Click on the “Network Connections” icon.
                                                                        4. Right click on the icon under the “LAN or High Speed
                                                                           Networking” option. Select Properties from the menu that
                                                                        5. You will see that the computer has a “Full Computer Name”
                                                                           and a “Workgroup”. Click the “Change” button to change
                                                                        6. Select the “Advanced” tab.
                                                                        7. Click on the “Allow other network users to connect...” option.
                                                                        8. Follow the directions in the dialog that appears.
                                                                                                 Windows 98

To access the printer from another computer:
1. Go to that computer and open the Printers window.
2. Double-click the Add a Printer wizard.
3. Choose the Network Printer option and click Next.                    By default, the ICS components are not installed on your
4. The wizard will display a list of all shared printers on the         computer. You only run ICS on the computer that is actually
   LAN. Choose the printer you wish to access and click Next            connected to the Internet:
  again. The wizard will then install the appropriate driver if it is
   available, or else request that you put in a disk or CD with the     1. Go to the Control Panel and double-click Add/Remove
  driver software.                                                        Programs.
                                                                        2. Select the Windows Setup tab and open the Internet Tools
Once the wizard finishes installing the software, the printer will         option.
appear to your system just like a local printer.                        3. Enable the Internet Connection Sharing component by clicking
             Networking Basics: Internet                                   on the box next to it and then clicking on OK.
                                                                        4. Once the ICS components are installed, the ICS wizard will
Microsoft recognized the growing popularity of home networks              pop up. Follow the prompts and keep clicking Next. If your
and first implemented Internet Connection Sharing (ICS) in                 Internet connection is not already configured on this computer,
Windows 98. This feature (much improved) is also available in              the wizard will open the Internet Connection Wizard (don’t get
Windows XP.                                                                 these two wizards confused!) so that you can set up an
ICS lets you connect one computer to the Internet by whatever              Internet connection. Simply follow the prompts. When you’re
means (modem, DSL, ISDN or cable) and share that connection                done, you’ll be returned to the ICS wizard.
with any other Windows 98/ME computer on the network.                   5. The ICS wizard will gather some information and prompt you
Though simple in theory, the first implementation of ICS proved            to insert a 3.5-inch diskette. This diskette will then be used to
problematic for many users. Windows 98 v.2 improved ICS, and               configure the other Windows 98/ME computers on your
Windows XP makes it even simpler.                                          network for Internet access.
                                                                Page 118
While file and printer sharing are still relatively easy on either
operating system, Internet-connection sharing using only
software can be a good deal trickier. In most cases, if you are
sharing a high-speed connection with several computers in your
home (and especially if you are doing it wirelessly) it is easier to
purchase a wireless hub/router and let it do the connection
sharing for you. Lynksys’ or Netgear’s wireless hubs/routers are
inexpensive, very easy to set up and also have the added benefit
of providing a hardware firewall to protect your network.
             Networking Basics: Routers
For less than $100, it is now possible to buy a router, a firewall, an
Ethernet hub and a wireless hub in one small package. A good
example is the Linksys Wireless-B Broadband Router. It is a
cable/DSL router with a built-in, four-port, 10/100-megabits per
second (Mbps) Ethernet hub and support for up to 8 megabytes
(MB) of bi-directional throughput (sends data both ways) at a            potential hackers. If an incoming packet of information is flagged
time. Computers in your home network connect to this little box          by the filters, it is not allowed through.
with a wireless card or with a network cable, and it in turn is          You should note that some spam is going to get through your
connected to either a cable or DSL modem. You configure the box          firewall as long as you accept e-mail. And, while some firewalls
using a Web-based interface that you reach through the browser           offer virus protection, it is worth the investment to install anti-
on your computer. However, you can simply plug it in and in 95%          virus software on each computer.
of the cases it will start working without any configuration at all.
Much of the work required to get information from one computer
to another is done by routers — they’re the crucial devices that
let information flow between, rather than within, networks.
Routers are specialized computers that send your messages, and
those of every other Internet user, speeding to their destinations
along thousands of pathways. When information needs to travel
between networks, routers determine how to get it there. A router
has two separate but related jobs:
* It ensures that information doesn’t go where it’s not needed.
  This is crucial for keeping large volumes of data from clogging        The level of security you establish will determine how many
   the connections of “innocent bystanders.”                             threats can be stopped by your firewall. You can restrict traffic
* It makes sure that information makes it to the intended                that travels through the firewall so that only certain types of
  destination(s).                                                        information, such as e-mail, can get through. The highest level of
                                                                         security would be to simply block everything. Obviously, that
In performing these two jobs, a router is extremely useful in            defeats the purpose of having an Internet connection. But a
dealing with two separate computer networks. It joins the two            common rule of thumb is to start out blocking everything, and
networks, your home network and the Internet in this case,               then begin to select what types of traffic you will allow. This is a
passing information from one to the other. It also protects the          good rule for businesses that have an experienced network
networks from one another, preventing the traffic on one from            administrator who understands what the needs are and knows
unnecessarily spilling over to the other. Regardless of how many         exactly what traffic to allow through. For most of us, it is prob-
networks are attached, the basic operation and function of the           ably better to work with the defaults provided by the firewall
router remains the same. Since the Internet is one huge network          developer unless there is a specific reason to change them.
made up of tens of thousands of smaller networks, routers are an
absolute necessity. For more information, see How Routers Work.          Windows XP provides a software firewall as part of the operating
See Figure Column 2.                                                     system. You can activate it from the same dialog you use to
                                                                         activate Internet Connection Sharing (see above).
            Networking Basics: Firewalls
                                                                         Hardware firewalls are incredibly secure and not very expensive.
Whether you are one of the growing number of computer users              One of the best things about a firewall from a security standpoint
with fast, always-on Internet access or you’re still using a dial-up     is that it stops anyone on the outside from logging onto a
connection, you may want to consider implementing a firewall. A          computer in your private network.
firewall is simply a program or hardware device that filters the
information coming through the Internet connection into your
private network or computer system. You use a firewall to protect
your home network and family from offensive Web sites and
                                                               Page 119
                    Building a Network
You’ve learned how to make your computer recognize other
computers in its network and begin sharing printers, files and an
Internet connection. We’ll now look closely at four types of
home computer networks - how each works, what each costs and
what the pros and cons are. The options we will discuss are:
* Ethernet networking * Phone-line networking * Power-line
  networking * Wireless networking * Ethernet Networking
Ethernet is easily the most popular networking system available
today. It is also one of the widest ranging systems. The equip-
ment needed for an Ethernet-based network can be as simple as
two network interface cards (NIC) and a cable, or as complex as
multiple routers, bridges and hubs. It is this versatility that makes
it so useful to businesses. We will focus on the basics for              To connect more than two computers using Ethernet, you
creating a home network.                                                                will need a hub like this.

                        Pros and Cons
                                                                        connect four computers, an 8-port hub can connect up to eight
Ethernet has many advantages:                                           computers and so on. Most hubs are stackable. A stackable hub
* It is the fastest home-networking technology (100 Mbps).              has a special port that can connect it to another hub to increase
* It can be inexpensive if the computers are close to one another.      the capacity of your network. So if you start with a four-port hub
* It is extremely reliable.                                             but eventually have five computers, you can buy another four-
* It is easy to maintain after it is set up.                            port hub and connect it to the one you already have, increasing
* The number of devices that can be connected is virtually              the potential number of computers on your network. A cable/DSL
 unlimited.                                                             router usually has a four-port Ethernet hub built in.
* There is a great deal of technical support and information            To connect the computers, you will need Unshielded Twisted Pair
 available.                                                             (UTP) Category 5 cable. This type of cabling is designed to
And a few disadvantages:                                                handle the 100-Mbps speed needed by Ethernet. The RJ-45
* If you have more than two computers, you’ll need additional           connector at the end of the cable looks very similar to the RJ-11
  equipment.                                                            connector on a phone cord but is slightly bigger (and not
* It can be expensive if wiring and jacks need to be installed.         compatible). You can buy Cat 5 cables in predetermined lengths
* Set-up and configuration can be difficult.                            with the connectors already attached. If you plan to install the
* The technical jargon and the number of options can be                 Cat 5 cabling in the walls of your house, you can buy the cable in
  confusing.                                                            rolls, cut it to length and connect the cable to special RJ-45 wall
                                                                        boxes. Unless you have done this type of installation before, you
           What You Need for Ethernet                                   will probably want to hire a professional.
Ethernet is available in two speeds: 10 Mbps and 100 Mbps.              Because of the large number of possible configurations in an
Most NICs are capable of operating at either speed, but you             Ethernet network, you most likely will not have any type of
should check to be sure before purchasing. Get cards capable of         automated installation software. This means that you will have to
the 100-Mbps data rate — the difference in cost is minimal. A 100-      manually configure all the options as we discussed at the
Mbps card costs about $15 to $40, and a 10/100-Mbps card costs          beginning of this article. If you have problems, the best source of
about $25 to $50.                                                       information is probably the manufacturer of whichever NIC cards
                                                                        you decide to use. For more information, see How Ethernet
There are two different ways to connect Ethernet cards: coax and
Cat 5 cabling. Coax was once the more popular of the two, but
today just about everyone uses Cat 5 because it is easier to            If you don’t mind running the cables along the floor, you can
configure. Cat 5 has a cable that looks a lot like a telephone cable.   install an Ethernet network for two computers in your home for
You run one cable to each computer, and each cable connects to          $100 or less. That includes the cost of two Ethernet cards, a small
a hub at the other end. A basic hub for a home network is a small       hub and two cables. Each additional computer will cost about $30
box that typically costs from $25 to $50 (depending on its speed        to $40 to connect using inexpensive network cards.
and how many connections it can support).
                                                                        Note: If you want to connect just two computers, you can avoid
To connect more than two computers using Ethernet, you will             the hub and use a crossover Cat 5 cable. With a crossover cable,
need a hub like this.                                                   you directly connect one NIC card to the other without a hub.
                                                                        This only works for two computers — to connect more than two
The hub takes the signal from each computer and sends it to all
                                                                        you need a hub.
of the other computers in your home. Hubs come in several sizes,
noted by the number of ports available — a four-port hub can
                                                             Page 120
                                                                     In 1984, Apple Computer introduced its Apple IIc model (click
    Good Boot Guide to Your Laptops                                  here for picture). The Apple IIc was a notebook-sized computer,
                                                                     but not a true laptop. It had a 65C02 microprocessor,128 kilobytes
Maybe you have been thinking about buying a computer, and it         of memory, an internal 5.25-inch floppy drive, two serial ports, a
has occurred to you that you might want to buy a laptop version.     mouse port, modem card, external power supply, and a folding
After all, today’s laptops have just as much computing power as      handle. The computer itself weighed about 10 to 12 lb (about 5
desktops, without taking up as much space. You can take a            kg), but the monitor was heavier. The Apple IIc had a 9-inch
laptop on the road with you to do your computing or make             monochrome monitor or an optional LCD panel. The combination
presentations. Perhaps you prefer comfortably working on your        computer/ LCD panel made it a genuinely portable computer,
couch in front of the TV instead of sitting at a desk. Maybe a       although you would have to set it up once you reached your
laptop is for you. In this edition of How Stuff Works, we will       destination. The Apple IIc was aimed at the home and educa-
examine how these portable computers do the same work as             tional markets, and was highly successful for about five years.
larger computers, but in much smaller packages.                      Later, in 1986, IBM introduced its IBM PC Convertible. (click here
                                                                     for a picture.) Unlike the Apple IIc, the PC Convertible was a true
                                                                     laptop computer. Like the Gavilan computer, the PC Convertible
                                                                     used an 8088 microprocessor, but it had 256 kilobytes of memory,
                                                                     two 3.5-inch (8.9-cm) floppy drives, an LCD, parallel and serial
                                                                     printer ports and a space for an internal modem. It came with its
                                                                     own applications software (basic word processing, appointment
                                                                     calendar, telephone/address book, calculator), weighed 12 lbs (5.4
                                                                     kg) and sold for $3,500. The PC Convertible was a success, and
                                                                     ushered in the laptop era. A bit later, Toshiba was successful with
                                                                     an IBM laptop clone.
                                                                     Since these early models, many manufacturers have introduced
                                                                     and improved laptop computers over the years. Today’s laptops
                                                                     are much more sophisticated, lighter and closer to Kay’s original
                                                                               Anatomy of a Laptop Computer
                                                                     To illustrate the parts of a laptop computer, we will show you the
                                                                     inside of a Toshiba Satellite Pro laptop.
                                                                                                                Toshiba Satellite Pro
                                                                                                                laptop computer
                     A Brief History
Alan Kay of the Xerox Palo Alto Research Center originated the
idea of a portable computer in the 1970s. Kay envisioned a
notebook-sized, portable computer called the Dynabook that
everyone could own, and that could handle all of the user’s
informational needs. Kay also envisioned the Dynabook with
wireless network capabilities. Arguably, the first laptop computer                                               The major parts of
was designed in 1979 by William Moggridge of Grid Systems
Corp. It had 340 kilobytes of bubble memory, a die-cast magne-
sium case and a folding electroluminescent graphics display
screen (click here for a picture). In 1983, Gavilan Computer
produced a laptop computer with the following features:
* 64 kilobytes (expandable to 128 kilobytes) of random access
  memory (RAM)
* Gavilan operating system (also ran MS-DOS)
* 8088 microprocessor
* touchpad mouse
* portable printer
* weighed 9 lb (4 kg) alone or 14 lb (6.4 kg) with printer
The Gavilan computer had a floppy drive that was not compatible
with other computers, and it primarily used its own operating
system. The company failed.
                                                                                    the Toshiba Satellite Pro laptop
                                                             Page 121
Like all computers, laptops have a central brain called a micropro-   for laptop use. A typical laptop processor has features that
cessor, which performs all of the operations of the computer.         reduce power consumption and heat. For example, laptop
                                                                      processors often run at a lower voltage and often have multiple
The microprocessor:
                                                                      sleep or slow-down modes that significantly increase battery life.
* has a set of internal instructions stored in memory, and can        Typical laptop microprocessors include Motorola’s PowerPC
 access memory for its own use while working.                         family (used in Apple Macintosh computers), Intel’s Pentium and
* can receive instructions or data from you through a keyboard        Celeron families (used in PCs) and AMD’s K5 and K6 families
  in combination with another device (mouse, touchpad,                (used in PCs).
 trackball, trackstick).
* can receive and store data through several data storage
 devices (hard drive, floppy drive, Zip drive, CD/DVD drive).
* can display data to you on computer monitors (cathode ray
 monitors, LCD displays).
* can send data to printers, modems, networks and wireless
   networks through various input/output ports.
* is powered by AC power and/or batteries.

                                                                      Close-up of the Toshiba’s Intel 486 DX4 microprocessor.
                                                                      This microprocessor is no longer used in laptop computers.

                                                                                          Operating Systems
                                                                      The operating system is the set of pre-programmed instructions
                                                                      that tell the microprocessor what to do. Operating systems on
                                                                      laptops include Windows 98/2000/NT (Microsoft) and Mac OS,
                                                                      depending upon the type of computer (PC vs. Mac), and Linux
                                                                      (Linux is not an option for most consumers, but some third-party
                                                                      developers are writing applications for this operating system on
                                                                      Laptops have memory , both RAM and ROM, just like desktops.
                                                                      The laptop’s ROM chip contains the BIOS just as it does in a
                                                                      desktop computer. (See How Bios Works for details.) RAM
Schematic diagram showing the various parts of a laptop               stores the application software and data files while the computer
computer.                                                             is on. RAM differs on a laptop in that it uses a different form
                                                                      factor — that is, the size and shape of the modules that carry the
         How Laptops Are Like Desktops                                RAM. Manufacturers have to build laptops to be portable
                                                                      (smaller) and to withstand more jostling (durable) than a desktop
For the most part, laptops have the same major parts as desktops:     would ever get, so the memory modules have to be different.
* microprocessor * operating system * solid-state memory              While some laptops use a standard Small Outline Dual Inline
* disk drives * input/output ports * sound cards and speakers         Memory Module (SODIMM), others use the manufacturer’s
                      Microprocessors                                 proprietary memory modules. Most laptops should have at least
                                                                      64 MB of RAM to have sufficient memory to run operating
Like standard desktops, laptops are powered by microproces-           systems and applications software. Also, some laptops allow you
sors. The microprocessor is the brain of the laptop and coordi-       to upgrade the memory of your computer and come equipped
nates all of the computer’s functions according to programmed         with convenient access panels to plug in additional memory
instructions (that is, the operating system software). The DX-4       chips.
processor shown in the photo below is no longer used, but it is
typical of modern laptop microprocessors in that it is customized
                                                            Page 122

Access panel to the memory chips on the laptop’s

                                                                                Close-up of Toshiba’s CD-ROM drive.
                                                                    In addition to hard drives, most laptops have some type of
                                                                    removable disk storage system, such as floppy disks, Zip disks,
                                                                    compact discs (CD) and DVDs. There are three options for disk
                                                                    drives in laptops:
                                                                    * Some laptops have more than one bay built into the case for
                                                                      disk drives (such as floppy drive and CD-ROM drive).
                                                                    * Some laptops have one bay that you can swap or interchange
                                                                      various drives. You just pull one drive out and put another in:
       Disk DrivesClose -up of Toshiba’s memory chip                  * “cold-swappable” drive - You must turn the computer off,
                                                                        change drives, then reboot the computer.
                         Disk Drives                                  * “hot-swappable” drive - You can change the drives without
                                                                        turning the computer off. This feature saves you the time
Like desktops, laptops have various disk drive storage devices.
                                                                        involved in restarting the computer.
All laptops have an internal hard disk drive, usually 6 to 20
                                                                    * Some laptops have no internal drives. All drives are external
gigabytes (GB). The hard disk drive stores operating systems,
                                                                      and connected to the computer by cables. This feature allows
application programs and data files. Although the hard disk drive
                                                                      the laptop to be very small and thin.
works the same in a laptop as it does in a desktop, laptops
generally have less disk space than desktops and you will have                         Input/Output Ports
fewer choices for hard disk drives in laptops. The smaller hard
disk space is one of the chief limitations of laptops.              Computers need to talk to other devices (such as printers,
                                                                    modems and networks). Computers send and receive information
                                                                    through various input/output ports, which can include serial
                                                                    ports, parallel ports and Universal Serial Bus (USB) ports.

                                                                    The back panel of the Toshiba Satellite Pro laptop com-
                                                                    puter, showing the various input/output ports.
                                                                    In addition to ports, some laptops have expansion slots for
                                                                    PCMCIA standard adapter cards (Type I and Type II) or “PC “
                                                                    cards. These cards can be used to upgrade your laptop by
                                                                    adding memory, a modem, a network connection or a peripheral
              Close-up of Toshiba’s hard drive.                     device (for example, a CD-ROM drive).
                                                           Page 123

                                                                        The Toshiba Satellite Pro’s rechargeable battery.

                                                                    The battery life varies depending on the type of rechargeable
                                                                    battery (lithium batteries tend to hold their charge longer) and
The Toshiba Satellite Pro has a PC card for modem/                  how you use your computer (frequent use of disk drives con-
Ethernet connections.                                               sumes a lot of battery power). In addition to the main battery,
                                                                    laptops have other batteries to run clocks and backup CMOS
              Sound Cards and Speakers                              RAM.
Like desktops, most laptops are equipped with sound cards and
speakers so they can play music from CDs. However, the quality
of the speakers built into most laptops does not match that of
speakers for desktops, because space is a major limitation in a
laptop case. The Toshiba laptop that we dissected has a sound
card and jacks so you could hook up a microphone or head-
phones; it also has a small speaker for sound.

                                                                           The Toshiba Satellite Pro’s backup batteries.
                                                                    Many laptop computer models have power management software
                                                                    to extend the battery life, or conserve battery power when the
                                                                    battery is low. You may notice that as your battery gets low, your
                                                                    laptop runs slower. This effect is typically the result of internal
                                                                    power management software, and indicates that you should plug
                                                                    in the computer’s AC adapter, or quit and re-charge your battery.
      Sound card of the Toshiba Satellite Pro laptop.
                                                                    All laptops have some type of LCD display screen. Laptop LCD
       How Laptops Differ from Desktops                             displays can be:
                                                                    * 12 to 15 inches
Laptops differ from desktops in the following features:             * black-and-white (16 grayscale) or color (65,536 colors)
* power supply * displays * input devices                           * passive or active matrix - active matrix displays have sharper
* docking connections                                                 images and are easier to read
                                                                    * reflective or backlit - backlit screens are good for low-level
                        Power Supply                                  room lighting conditions
Like desktops, laptops can be plugged into the wall to receive AC
power from the electric power grid through an AC adapter. But
what makes the laptop unique is that it is portable; so, laptops
are also powered by batteries. All laptops use some type of
rechargeable battery (lithium, nickel-cadmium, nickel-metal

                                                                               Front view of the Toshiba’s LCD panel.
                                                              Page 124

Back view of the Toshiba’s LCD panel, showing the fluo-
rescent tube that provides the light and the screen that
diffuses the light evenly over the surface.                            Close-up of a touchpad from another laptop computer.

Modern laptop computers have 800 x 600 pixel resolution, which                          Docking Connections
makes for a clear screen; anything less than this resolution
should be avoided.                                                   Some people find that it is difficult or uncomfortable to use a
                                                                     laptop at their desk. The screen may be too small to see ad-
                         Input Device                                equately. The keyboard may be slightly smaller than a standard
For a desktop computer, you typically use a keyboard and mouse       keyboard. The touch pad may not be as comfortable to use as a
to enter data. However, because using a mouse takes up room,         mouse. Perhaps they want to have access to more than one type
other devices are built into laptops to take its place. Laptops      of disk drive. To make the laptop more convenient for desktop
come with one of three input devices:                                use, the docking station was invented. The docking station has
                                                                     several peripheral devices (full-size computer monitor, full-size
* trackball - rotating the ball allows you to move the cursor on
                                                                     keyboard, mouse, disk drives, printer) connected to it. You just
  the LCD screen
                                                                     plug your laptop into the station to use it as a desktop computer;
* trackpoint - pushing your finger over the point allows you to
                                                                     in other words, you make one connection to your laptop instead
   move the cursor
                                                                     of many. Most laptops have a docking connection.
* touchpad - moving your finger across the pad allows you to
   move the cursor
All of these devices have buttons that act like the right and left
buttons on a mouse. Also, most laptops have a port that allows
you to hook up a mouse to your laptop if you wish.

                                                                     Close-up view of the docking connection on the back of the
                                                                     Toshiba Satellite Pro.

                                                                     Features that affect the performance of the computer include:
                                                                     * microprocessor * operating system * RAM * disk drives
                                                                     * display * battery * input/output ports * fax/modem
                                                                     * sound cards and speakers

                                                                     Like standard desktops, laptops are powered by microproces-
                                                                     sors. The microprocessor is the brain of the laptop and coordi-
                                                                     nates all of the computer’s functions according to programmed
Close-up of the Toshiba’s keyboard, showing the trackpoint           instructions (i.e. the operating system software). For Apple
device.                                                              Macintosh users, the choice of microprocessor is limited.
                                                                     Powerbooks and iBooks are equipped with special processors
                                                                     designed for use with Apple Laptops only. For PC users, there is
                                                            Page 125
a wider variety. You can choose from Intel’s Pentium and Celeron    * Some laptops have more than one bay built into the case for
families or AMD’s K5 and K6 families. Powerful Pentium micro-         disk drives (such as a floppy drive or a CD-ROM drive).
processors tend to be found in high-end laptops, whereas            * Some laptops have one bay that you can swap or interchange
Celeron and AMD chips tend to be found in lower-end models.           various drives. You just pull one drive out and put another in:
The choice between these chips depends upon your needs for            * “cold-swappable” drive - You must turn the computer off,
speed versus cost. Click here for a discussion of the differences       change drives, and then reboot the computer.
between Pentium and Celeron chips.                                    * “hot-swappable” drive - You can change the drives without
                                                                        turning the computer off. This feature saves you the time
                    Operating Systems                                   involved in restarting the computer.
The operating system is the set of pre-programmed instructions      * Some laptops have no internal drives. All drives are external
that tells the microprocessor what to do.                             and connected to the computer by cables. This feature allows
                                                                      the laptop to be very small and thin.
You may also want to consider that the latest operating system
may not be the best one for your laptop. Operating systems vary                                 Displays
in their use of power management, security encryptions (in case
                                                                    All laptops have some type of LCD display screen. Laptop LCD
your laptop is stolen) and cost. See the Links section for
                                                                    displays can be:
information regarding the best operating system for your
notebook computer.                                                  * from 12 to 17 inches
                                                                    * passive or active matrix - active matrix displays have sharper
                             RAM                                      images and are easier to read
With all of the options out there, you may be wondering how         * reflective or backlit - backlit screens are good for low-level
much memory you need in your laptop. You should probably buy        room lighting conditions
a laptop with a minimum of 64 MB RAM. Also, check to see how        Large screen sizes, active matrix and backlighting make a better
much VRAM you have, because this will be important in running       display, but also increase the price of the computer. A 13- to 14-
graphics (minimum = 2 MB VRAM). Some laptops allow you to           inch, active matrix, color screen is worth the investment, though,
upgrade memory, and may have an easy access panel that              especially if you plan to search the Internet often or make
provides for convenient switching of memory chips. In other         multimedia presentations using your laptop.
upgradeable laptops, you have to open the case to get under the
keyboard to add memory, or send it to a repair technician.                                     Batteries
                                                                    To make laptops portable, they are powered by batteries. All
                                                                    laptops use some type of rechargeable battery (lithium, nickel-
                                                                    cadmium, nickel-metal hydride). The battery life varies, depend-
                                                                    ing upon the type of rechargeable battery (lithium batteries tend
                                                                    to hold their charge longer and have no memory effect) and how
                                                                    you use your computer (frequent use of disk drives consume a
                                                                    lot of battery power). A battery should have a minimum life of 2
                                                                    hours; of course, 4 hours is even better.
                                                                    Many laptop computer models have power management software
                                                                    to extend the battery life, or conserve battery power when the
                                                                    battery is low; power management software may be built into the
                                                                    operating system. You may notice that as your battery gets low,
                                                                    your laptop runs slower. This effect is typically the result of
                                                                    internal power management software, and indicates that you
In this Toshiba laptop, there is a convenient access panel          should plug in the computer’s AC adapter, or quit and re-charge
underneath that you can access to add memory.                       your battery. Laptops can be plugged into the wall to re-charge
                         Disk Drives                                the battery, or can be connected directly to AC power through an
                                                                    AC adapter.
Like desktops, laptops have various disk drive storage devices.
All laptops have an internal hard disk drive, usually 6 to 20 GB.   Laptop computer batteries can cost from $50 - $250 depending
You will have fewer choices in hard disk drives in a laptop than    upon the type of battery and computer. If you travel frequently,
you would in a desktop model, but 10 GB is a reasonable storage     especially if you travel long distances, then you may want to
capacity.                                                           consider buying an extra battery.

In addition to hard drives, most laptops have some type of                              Input/Output Ports
removable disk storage system, such as floppy disks, Zip disks,     Computers need to talk to other devices (e.g. printers, modems,
compact disks (CD) and digital video disks (DVD). There are         networks). Computers send and receive information through
three options for disk drives in laptops:                           various input/output ports which can include serial ports, parallel
                                                                    ports ethernet ports and Universal Serial Bus (USB) ports. At
                                                               Page 126
minimum, you should have a printer port, which is usually a            All of these devices have buttons that act like the right and left
parallel port, and one or two USB ports.                               buttons on a mouse.
In addition to ports, some laptops have expansion slots for
PCMCIA standard adapter cards (Type I and Type II) or “PC “
cards. These cards can be used to upgrade your laptop by
adding memory, a modem, a network connection, wireless
capabilities or a peripheral device. A PC card slot will help extend
the life of your laptop by allowing you to upgrade rather than
replace your laptop in the future.
You may want to look for a docking station port on your com-
puter. The docking station was invented to make the laptop more
convenient for desktop use. The docking station has several
peripheral devices (full-size computer monitor, full-size keyboard,
mouse, disk drives, printer) connected to it. You just plug your
laptop into the station, and you’re ready to use it as a desktop
computer; in other words, you make one connection to your
laptop instead of many. Most laptops have a docking connec-
                          Fax/Modem                                                 Some laptops have a touchpad input.
If you have to communicate with your company or customers              The type of device you want is purely a matter of preference.
while on the road, access e-mail, fax documents or access the          Some people prefer the feel of a trackball over a touch pad. If you
Internet, you will need a modem. Look for a laptop with an             can, try out various input devices to see what feels right to you.
internal fax/modem with a minimum of 56 kps, or an internal            Remember, most laptops have a port that allows you to hook up a
wireless card. This will allow you to send and receive information     mouse to your laptop; but again, that will be another device to
by just hooking up to a phone connection. If your laptop does          carry around if you want to use it on the go.
not have an internal fax/modem, you may be able to add one
through a PC card slot.                                                                            Keyboard
                                                                       Because space is a premium for laptops, their keyboards tend to
               Sound Cards and Speakers
                                                                       be smaller than desktop keyboards. Although you won’t find an
Like desktops, most laptops are equipped with sound cards and          ergonomic keyboard, like the Microsoft natural keyboard, on a
speakers so they can play music from CDs. However, the quality         laptop, most laptop keyboards have some ergonomic features,
of the speakers built into most laptops does not match that of         such as being located at the back half of the unit to provide wrist
speakers for desktops, because space is a major limitation in a        support. The arrow keys will most likely be in different places to
laptop case. If your laptop has no sound equipment, you can add        conserve space, and you may not have a numeric keypad. If you
it through a PC card slot. If sound quality is important to you,       can, try out several laptops to see if the keyboards feel comfort-
you can upgrade it by using external speakers.                         able; this is especially important for touch typists.
                         Convenience                                                          Size and Weight
Now that we have addressed features for performance, let’s             The size of the laptop is an important feature, seeing as the key
consider features for convenience:                                     advantage of a laptop is its portability. Consider the length, width
* type of input device * keyboard * size * weight * case               and thickness, and make sure it will fit in whatever you plan to
* feel * software * carrying case * Input Device                       carry it around in, if you have something in mind. If you can,
                                                                       when you are shopping for your laptop, pick it up and carry it as
For a desktop computer, you typically use a keyboard and mouse         you would a notebook. Does it feel comfortable?
to enter data. However, because using a mouse takes up room,
other devices are built into laptops to take its place. Laptops        Like size, weight is an important feature. Laptops vary in weight
come with one of three input devices that allow you to move the        from 4 to 10 lb (2 to 5 kg). If you will be traveling frequently, you
cursor on the LCD screen:                                              will probably want a light laptop (under 5 lb or 2 kg). Again, pick
* trackball - rotating the ball allows you to move the cursor on       up the laptop that you are interested in. Can you carry it easily?
   the LCD screen (usually built-in, but add-on ones that clip to                                      Case
   the side of your laptop are available)
* trackpoint - pushing your finger over the point moves the            Because you’ll be carrying the laptop, there’s a chance that
   cursor                                                              you’ll eventually drop it. Find out what material the manufacturer
* touchpad - moving your finger across the pad moves the               uses for the case. For example, the IBM Thinkpad has a titanium
   cursor                                                              composite cover. This is a hard criteria to test out (the store
                                                                       won’t be happy if you drop every laptop you’re interested in),
                                                                       but it would still be useful to know.
                                                             Page 127
                              Feel                                    best operating system for a laptop. See the Links section for
                                                                      information regarding the best operating system for your
Again, check out several models of laptops before you buy. Does
                                                                      notebook computer.
the keyboard feel comfortable in combination with the input
device? Is the screen large enough to see easily? We have talked      Make sure you have at least 64 MB of RAM.
about individual features separately, but it is important to check    Look for easily upgradeable memory. Does your laptop have
them out together to assess the overall feel of the model. Comfort    an easy access panel to get at the memory chips? Do you have to
is key in a laptop.                                                   open the case to get under the keyboard to add memory? Do you
                           Software                                   have to send it to a repair technician?

Keep in mind what you intend to use your laptop for when              Know your battery life! Your battery is essential to the
you’re shopping. Many laptops have software packages pre-             portability of your laptop. Batteries will die. You will need a
installed or included in the box. Most tend to be word processing     minimum of two hours of battery life; of course, four hours is
software, like Microsoft Word, or integrated software such as         even better. The battery life varies depending on what type of
Microsoft Works or ClarisWorks. Check to see if the included          rechargeable battery you use (lithium batteries tend to hold their
software matches your needs; otherwise, you may have to spend         charge longer and have no memory effect) and how you use your
several hundred dollars extra to get the appropriate software.        computer (frequent use of disk drives consume lots of battery
Also, does the computer have sufficient memory and micropro-          power). Also, look at the battery gauge in your software fre-
cessor speed to run the software you plan to use?                     quently so that you are not in the middle of some important
                                                                      project when your battery dies.
                        Carrying Case
                                                                      Count the input/output ports. Computers send and receive
Although carrying cases are not standard with laptop computers,       information through various input/output ports, which can
consider spending the extra money to purchase a good one. Look        include serial ports, parallel ports and Universal Serial Bus (USB)
for a carrying case that has the following features:                  ports. At minimum, you should have a printer port, which is
* lightweight                                                         usually a parallel port, and one or two USB ports.
* rests comfortably on your shoulder (padded shoulder strap)
                                                                      One or two PC slots will help extend the life of your laptop by
* waterproof or water-resistant (after all, you may have to walk in
                                                                      allowing you to upgrade rather than replace your laptop in the
  the rain)
* has enough space for your computer and accessories (disk
  drives, disks, AC adapter)                                          Look for an internal fax/modem! If you have to communicate
* has a padded compartment to protect the laptop should you           with your company or customers while on the road, access e-
  drop the carrying case                                              mail, fax documents or access the Internet, then you will need a
                                                                      modem. Look for a laptop with an internal fax/modem (minimum
                                                                      56 kps), because lugging a modem around with you is far from
Laptop computers vary in price from about $1,000 to $4,000 or         ideal. Adding a wireless card will allow you to accsess the
more, depending on the various features. Low-end laptops range        Internet with a wireless connection.
from $1,200 to $1,600. Many retailers are offering $30 to $400 in
                                                                      Test out the input device. Laptops use either a trackball,
rebates if you contract with a particular Internet service provider
                                                                      trackpoint or touch-pad to move the cursor across the screen. All
(ISP). If you do not have a current ISP, this might be a reasonable
                                                                      of these devices have buttons that act like the right and left
way to reduce the cost of your laptop. Note that the contracts
                                                                      buttons on a mouse. The type of device you choose is totally a
usually lock you into one particular provider for two to three
                                                                      matter of personal preference. Some people prefer the feel of a
                                                                      trackball to a touch pad. If you can, try out the various input
                          Look Out!                                   devices to see what feels right for you. Remember, most laptops
                                                                      have a port that allows you to hook up a mouse to your laptop, if
When buying a laptop computer, there are several things you           you wish, but that will be another device to carry around if you
should keep in mind to avoid buying one that won’t meet all your      want to use it on the go.
needs. Here are some of the most important things to think about:
                                                                      Check the feel of the keyboard. Laptop keyboards tend to
Make sure the microprocessor meets your needs. If you                 be smaller than desktop keyboards. If you can, try out several
will be doing lots of graphics or programming, you will probably      laptops and see if the keyboards feel comfortable to you; this is
need the speed of the most powerful processor available at the        especially important for touch typists.
time. If you will use your laptop for basic word-processing, Web
browsing or office management, then the AMD or Celeron                Look at the software. Keep in mind what you intend to use
microprocessors will be fine.                                         your laptop for when you buy it. Many laptops have software
                                                                      packages pre-installed or included in the box. Most tend to be
The latest operating system may not be the best for your              word processing software (Microsoft Word) or integrated
laptop. Operating systems vary in their use of power manage-
                                                                      software (such as Microsoft Works or ClarisWorks). Check to see
ment, security encryptions (in case your laptop is stolen) and        if the included software matches your needs; otherwise, you may
cost. The best operating system for a desktop may not be the
                                                              Page 128
have to spend several hundred dollars extra to get the appropri-       screen easier to see, but these technologies will also increase the
ate software. Also, does the computer have sufficient memory           price of the computer. A 13- to 14-inch, active matrix, color screen
and microprocessor speed to run the software you intend to use?        is worth the investment, especially if you plan to search the
                                                                       Internet often or make multimedia presentations.
Check the warranty. Read the fine print. A good warranty will
cover parts and labor for three years. Also, toll-free, around-the-    What type of input/output ports should my laptop have?
clock technical support is great. Some warranties may have a 24-       Computers send and receive information through various input/
hour replacement/repair policy (good when you are away from            output ports, which can include serial ports, parallel ports and
home). If these features are not in your warranty, consider a          Universal Serial Bus (USB) ports. At minimum, you should have a
supplemental extended service contract.                                printer port, which is usually a parallel port, and one or two USB
                                                                       What is a PC card slot? In addition to ports, some laptops
What is the best microprocessor? If you do lots of graphics
                                                                       have expansion slots for PCMIA standard adapter cards (Type I
(computer-aided drafting, engineering design) or programming,
                                                                       and Type II) or “PC “ cards. These cards can be used to upgrade
then you will probably need the speed of a Pentium III or G4
                                                                       your laptop by adding memory, a modem, a network connection
microprocessors. On the other hand, if you will use your laptop
                                                                       or a peripheral device (such as a CD-ROM drive). One or two PC
for basic word-processing, Web browsing or office management,
                                                                       slots will help extend the life of your laptop by allowing you to
then the AMD or Celeron microprocessors will be fine.
                                                                       upgrade rather than replace your laptop in the future.
How much memory do I need? You should have at least 64
                                                                       What is a docking station?
MB of RAM. Check to see whether your memory is upgradeable.
If so, then your laptop should have an easy access panel to get        If you will use your laptop as a desktop as well, you may want to
at the memory chips.                                                   look for a docking station. With the docking station, you can
                                                                       connect several peripheral devices (full-size computer monitor,
How long will my battery last? You should look for a laptop
                                                                       full-size keyboard, mouse, disk drives, printer) permanently. You
with a lithium battery, because lithium batteries tend to hold their
                                                                       just plug your laptop into the station, and you’re ready to use it
charge longer than nickel-cadmium or nickel-metal hydride
                                                                       as a desktop computer; in other words, you make one connection
batteries, and have no memory effect. Whatever battery you
                                                                       to your laptop instead of many. Most laptops have a docking
choose, you will need a minimum of two hours of battery life; but
of course, four hours is even better. The battery life varies
depending on what type of rechargeable battery you have and            Which type of input device is the best? Laptops use either a
how you use your computer (frequent use of disk drives con-            trackball, trackpoint or touchpad technology to move the cursor
sumes a lot of battery power).                                         across the screen. All of these devices have buttons that act like
                                                                       the right and left buttons on a mouse. The type of device you
How much space should my hard drive have? All laptops
                                                                       choose in a matter of personal your preference. Some people
have an internal hard disk drive, usually 6 to 20 GB (10 GB is a
                                                                       prefer the feel of a trackball to a touch pad. If you can, try various
reasonable storage capacity).
                                                                       input devices out to see what feels right for you. Remember, most
What other drives should I have in my laptop? You should               laptops have a port that allows you to hook up a mouse to your
have at least a standard floppy drive; you may want a higher           laptop, if you wish, but that will be another device to carry
capacity Zip drive as well. Also, if you want to be able to play       around if you want to use it on the go.
music or movies on your laptop, you’ll need a CD-ROM or DVD-
                                                                       Do I need to buy a carrying case? A carrying case provides
ROM drive.
                                                                       a single place to store your laptop and its accessories. If you
What is a swappable drive? To make the laptop smaller and              travel frequently, you will definitely need one. Look for a carrying
lighter, many models have “swappable” or interchangeable               case that has the following features:
drives. With a swappable drive, there is only space in the case for    * lightweight
one drive (floppy drive, Zip drive or CD/DVD drive). If you want       * fits comfortably on your shoulder (padded shoulder strap)
to change from one type of disk drive to another, you just pull        * waterproof or water-resistant (After all, you may have to walk
one out of the bay and put the other one in. In some laptops with        in the rain.)
swappable drives, you must turn the computer off first, change         * has enough space for your computer and accessories (disk
the drive and then reboot the computer. Other laptop models may          drives, disks, AC adapter)
have a “hot swappable” drive, in which you can interchange the         * has a padded compartment to protect the laptop should you
drives without turning the computer off; this feature saves you          drop the carrying case
the time involved in restarting the computer. While swappable
                                                                       Should I buy an extended warranty? Read the fine print of
drives allow you to use several types of drives in your laptop,
remember that you will have to carry those extra drives with you       your warranty. A good warranty will cover parts and labor for
if you want to use them on the go.                                     three years. Also, toll-free, around-the-clock technical support is
                                                                       great. Some warranties have a 24-hour replacement/repair policy
What type of screen should I get? Large LCD screen sizes,              (good when you are away from home). If these features are not in
active matrix displays and backlighting will make your laptop’s        your warranty, consider a supplemental extended service
                                                           Page 129

       Good Boot Guide to Your PDA

You have been carrying around your big notebook/organizer that
has your address book, daily planner, to-do lists, memo pads,
calendar, project lists and expense reports - everything that you
need to keep your life organized. It’s bulky, heavy and stuffed
full, but if you don’t have it, you’re lost. But as you jot down
appointments on your calendar or look up phone numbers in
your address book, you see other people everywhere - in
business meetings, at the airport, around the supermarket -
scribbling things on a device that is about the size of a small
calculator or maybe the size of a paperback book. They have
traded their calendars and address books for a personal digital
assistant, or PDA, a remarkable, tiny, fully functional computer
that you can hold in one hand. And unlike that paper organizer, a
PDA can hold your downloaded e-mail and play music.
                                                                                 The parts that can make up a PDA
PDAs are the one of the fastest selling consumer devices in
                                                                    PDAs fall into two major categories: hand-held computers and
history. More than 9 million hand-held computers have been
                                                                    palm-sized computers. The major differences between the two are
sold, the vast majority of them from one company, Palm Comput-
                                                                    size, display and mode of data entry. Compared to palm-sized
ing. But other companies are breaking into the market. Competi-
                                                                    computers, hand-held computers tend to be larger and heavier.
tion means that you have more features to choose and decisions
                                                                    They have larger liquid crystal displays (LCD) and use a minia-
to make if you are thinking about buying a PDA. In this article,
                                                                    ture keyboard, usually in combination with touch-screen
we will examine how these devices receive information, process
                                                                    technology, for data entry. Palm-sized computers are smaller and
information, and communicate with other computers and PDAs.
                                                                    lighter. They have smaller LCDs and rely on stylus/touch-screen
                        PDA Basics                                  technology and handwriting recognition programs for data entry.

The idea of making a small hand-held computer for storing                                   PDA Parts
addresses and phone numbers, taking notes and keeping track of
                                                                    Regardless of the type of PDA, they all share the same major
daily appointments originated in the 1990s, although small
computer organizers were available in the 1980s. One of the first
                                                                    * microprocessor * operating system * solid-state memory
PDAs that was commercially available was Apple Computer’s
                                                                    * batteries * LCD display * input device * input/output
Newton Message Pad. The Newton was too big, expensive and           ports * buttons in combination with touch-screen or
complicated, and its handwriting recognition program was poor.      keyboard * desktop PC software
Other companies attempted to make a PDA with little success.
In 1996, the original Palm Pilot was introduced, and it was a hit
with consumers. It was small and light enough to fit in a shirt     Like standard desktop and laptop computers, PDAs are powered
pocket, ran for weeks on AAA batteries, was easy to use and         by microprocessors. The microprocessor is the brain of the PDA
could store thousands of contacts, appointments and notes.          and coordinates all of the PDA’s functions according to pro-
Today, you can buy Palm-like devices from major PC hardware         grammed instructions. Unlike desk and laptop PCs, PDAs use
manufacturers (Hewlett-Packard, IBM, Compaq, Sony). Though          smaller, cheaper microprocessors, such as the Motorola
originally intended to be simple digital calendars, PDAs have       Dragonball, Multiprocessor without Interlocked Pipeline Stages
evolved into machines for crunching numbers, playing games or       (MIPS), or Hitachi’s SH7709a. Although these microprocessors
music and downloading information from the Internet. All have       tend to be slower than their PC counterparts (16-75 MHz,
one thing in common: They’re designed to complement a desktop       compared with up to 1,000 MHz in PCs), they are adequate for the
or laptop computer, not replace one.                                tasks that PDAs perform. The benefits of small size and price
                                                                    outweigh the cost of slow speeds.
                                                               Page 130
                                                                      A PDA doesn’t have a hard drive. It stores basic programs
                                                                      (address book, calendar, memo pad and operating system) in a
                                                                      read-only memory (ROM) chip, which remains intact even when
                                                                      the machine shuts down. Your data and any programs you add
                                                                      later are stored in the device’s RAM. This approach has several
                                                                      advantages over standard PCs. When you turn on the PDA, all
                                                                      your programs are instantly available. You don’t have to wait for
                                                                      applications to load. When you make changes to a file, they’re
                                                                      stored automatically, so you don’t need a Save command. And
                                                                      when you turn the device off, the data is still safe, because the
                                                                      PDA continues to draw a small amount of power from the
                                                                      All PDAs use solid-state memory; some use Static RAM and
                                                                      some use Flash memory. Some are even incorporating removable
                                                                      forms of memory. PDAs usually come with 2 MB minimum of
    Motorola Dragonball microprocessor in a Palm M100                 memory. One megabyte of memory can store up to 4,000 ad-
                                                                      dresses and 100 e-mail messages. However, many application
                     Operating Systems                                programs take up memory space, so more advanced models
The operating system contains the pre-programmed instructions         usually have more memory (5 to 32 MB). Also, PocketPC takes
that tell the microprocessor what to do. The operating systems        more memory space so PDAs with this operating system usually
used by PDAs are not as complex as those used by PCs. They            have 16 or 32 MB. In some PDA models, the amount of memory is
generally have fewer instructions and take up less memory. For        upgradeable.
example, the Palm operating system fits in less than 100K of                                     Batteries
memory, which is less than 1 percent the size of Windows 98 or
                                                                      PDAs are powered by batteries. Some models use alkaline (AAA)
the Mac OS. PDAs typically have one of two types of operating
                                                                      batteries, while others use rechargeable batteries (lithium, nickel-
systems, Palm OS (3Com) or PocketPC (formerly called Windows
                                                                      cadmium or nickel-metal hydride). The battery life depends on
CE, Microsoft). Palm OS takes up less memory and runs faster,
                                                                      what kind of PDA you have and what you use it for. Here are
and most users say it is easier to use. PocketPC easily supports
                                                                      some of the things that can drain batteries:
color displays, graphics, miniaturized Windows packages (Word,
Excel), and other devices (such as built-in MP3 players or MPEG       * Operating system - PocketPC requires more power by virtue of
movie players). PocketPC takes up more memory and is slower,            its increased memory requirements.
and users say it is more complicated. As of this writing, Palm OS     * More memory
dominates the market, but PocketPC is challenging. Other              * Color LCD display
companies are developing software for both operating systems.         * Voice recording
                                                                      * MP3 player
Here is an inside view of a PDA. The circuit board folds away
from the screen. In the middle of the single-layer circuit board is   Battery life can vary from two hours to two months depending
the microprocessor, and to the left and above are the memory          upon the PDA model and its features. Most PDAs have power
chips.                                                                management systems in place to extend the battery life. Even if
                                                                      the batteries are so low that you can no longer turn the machine
                                                                      on (it will give you plenty of warning before this happens),
                                                                      there’s usually enough power to keep the RAM refreshed. If the
                                                                      batteries do run completely out of juice or if you take them out of
                                                                      the machine, you’ll have about a minute to replace them before
                                                                      the transistors inside the device lose their charge. At this point,
                                                                      most PDAs lose all their data, which makes backing up a PDA on
                                                                      a desktop or a laptop extremely important. PDAs also come with
                                                                      AC adapters to run off household electric current.
                                                                                               LCD Display
                                                                      PDAs have some type of LCD display screen. Unlike the LCD
                                                                      screens for desktop or laptop computers, which are used solely
                                                                      as output devices, PDAs use their screens for output and input.
                                                                      The LCD screens of PDAs are smaller than laptop screens, but
                                                                      vary in size. Hand-held computers generally have larger screens
                                                                      than palm-sized computers. PDA displays have the following
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* LCD, enhanced LCD, or color super-twist nematic (CSTN)                a touch screen that lets you launch programs by tapping on the
  types (See How LCDs Work for details.)                                screen with a pen-like stylus or enter your data by writing on it.
* pixel resolutions (160 x 160, 240 x 320)
                                                                        Think of the Palm’s screen as a multilayer sandwich. On top is a
* black-and-white (16 grayscale) or color (65,536 colors)
                                                                        thin plastic or glass sheet with a resistive coating on its bottom.
* passive or active matrix - active matrix displays have sharper
                                                                        The plastic or glass floats on a thin layer of nonconductive oil,
  images and are easier to read
                                                                        which rests on a layer of glass coated with a similar resistive
* reflective or backlit - backlit screens are good for reading in low
                                                                        finish. Thin bars of silver ink line the horizontal and vertical
                                                                        edges of the glass. Direct current is applied alternately to each
                                                                        pair of bars, creating a voltage field between them.
                                                                        When you touch the stylus to the screen, the plastic pushes
                                                                        down through the gel to meet the glass (called a “touchdown”).
                                                                        This causes a change in the voltage field, which is recorded by
                                                                        the touch screen’s driver software. By sending current first
                                                                        through the vertical bars and then the horizontal ones, the touch
                                                                        screen obtains the X and Y coordinates of the touchdown point.
                                                                        The driver scans the touch screen thousands of times each
                                                                        second and sends this data to any application that needs it. In
                                                                        this way, the PDA knows when you’re tapping an on-screen icon
                                                                        to launch a program or gliding it across the screen to enter data.
                                                                        Now let’s look at how the handwriting recognition works. Using a
                                                                        plastic stylus, you draw characters on the device’s touch screen.
                                                                        Software inside the PDA converts the characters to letters and
                                                                        numbers. However, these machines don’t really recognize
                                                                        handwriting. Instead, you must print letters and numbers one at a
                                                                        time. On Palm devices, the software that recognizes these letters
                                                                        is called Graffiti. Graffiti requires that each letter to be recorded in
                                                                        one uninterrupted motion, and you must use a specialized
                                                                        alphabet. For example, to write the letter “A,” you draw an
                                                                        upside-down V. The letter “F” looks like an inverted L. To make
                                                                        punctuation marks, you tap once on the screen and draw a dot
                                                                        (for a period), a vertical line (for an exclamation point), and so on.
                                                                        To help Graffiti make more accurate guesses, you must draw
                                                                        letters on one part of the screen and numbers in another part.
                                                                        The disadvantage of handwriting recognition software is that
                                                                        you have to learn a new way to write, it’s slower than normal
                                                                        handwriting and the device’s character recognition is rarely
                                                                        letter-perfect. On the other hand, it’s surprisingly easy to learn
                                                                        and it works. Some PDAs let you enter data anywhere on screen
                                                                        and employ different recognition software (for example, Jot) that
Here are the parts of the PDA - the case, the LCD                       doesn’t require a special alphabet (but still works better if you
screen and the circuit board. This model comes in basic                 draw your letters a particular way).
black, but you can buy interchangeable covers in various
colors.                                                                 If you can’t get the hang of PDA handwriting, you can use an
                                                                        onscreen keyboard. It looks just like a regular keyboard, except
                         Input Device                                   you tap on the letters with the stylus. An accessory to some
PDAs vary in how you can input data and commands. Hand-held             palm-sized computers is a collapsible keyboard that plugs into
computers typically use a miniature keyboard in combination             your PDA, which is more practical than handwriting if you use
with a touch screen. Palm-sized computers use a stylus and              the device to send e-mail.
touch screen exclusively in combination with a handwriting              Eventually, most PDAs will incorporate voice recognition
recognition program. Each model also has a few buttons to bring         technology, where you speak into a built-in microphone while
up screens or applications. Let’s take a closer look at how a           software converts your voice waves into data.
stylus/touch screen works.
                                                                                           Input/Output Devices
The tiny, four-inch screen on a palm-sized computer serves as an
output and an input device. It displays information with an LCD,        Because PDAs are designed to work in tandem with your
similar to that you’d find on a laptop. But on top of the LCD sits      desktop or laptop, they need to work with the same information
                                                                        in both places. If you make an appointment on your desktop
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computer, you need to transfer it to your PDA; if you jot down a     hand-writing recognition software. This involves learning some
phone number on your PDA, you should upload it later to your         shorthand alphabet, such as Palm’s Graffiti, which can take some
PC. You also need to be able to save everything on the PDA to a      time to master fully.
desktop computer in case the batteries go dead in the PDA. So,
any PDA must be able to communicate with a PC. The communi-
                                                                                          Operating System
cation between PDA and PC is referred to as data synchroniza-        This is one of the most important decisions to make! It is
tion or syncing. This is typically done through a serial or USB      the PDA equivalent to “Should I buy an Apple Macintosh or
port on the PDA. Some PDAs have a cradle that they sit in while      IBM PC/PC clone?” The operating system used by PDAs are one
hooked up to the PC.                                                 of two types, Palm OS (3Com) or PocketPC (formerly called
                                                                     Windows CE, Microsoft). Palm OS takes up less memory, runs
In addition to communicating through a cable, many PDAs have
                                                                     faster, and is easier to use. PocketPC easily supports color
an infrared communications port that uses infrared (IR) light to
                                                                     displays, graphics, standard Windows packages (Word, Excel),
beam information to a PC or another PDA. Some PDAs also offer
                                                                     and other devices (e.g., built-in MP3 players, MPEG movie
wireless methods to transfer data to and from a PC/PC network
                                                                     players); however, PocketPC takes up more memory, is slower,
through a wireless e-mail /Internet service provider like those
                                                                     and more complicated to use. However, if it is important to be
available on new models of cell phones. Finally, some PDAs offer
                                                                     able to exchange files with Windows packages, then PocketPC
telephone modem accessories to transfer files to and from a PC/
                                                                     might be a better choice. As of this writing, Palm OS dominates
PC network.
                                                                     the market because its operating system is specifically tailored to
             Desktop/Laptop PC Software                              the basic uses of a PDA. However, PocketPC is challenging Palm
                                                                     OS, and third-party software developers exist for both operating
To sync your data to or from your PDA, you install a synchroni-
zation utility (HotSync for Palm OS, ActiveSync for PocketPC) on
your computer’s hard drive to connect the PDA to your PC                                          Display
(cable, IR, wireless, modem). You’ll also need to have versions of
                                                                     All PDAs have LCD displays. PDA displays have the following
your hand-held’s address book, calendar and other important
applications installed on your desk or laptop, or use a personal
information manager (PIM) like Lotus Organizer or Microsoft          * Color vs. monochrome - Most PDAs are black-white (16 gray
Outlook that supports syncing. The PDA assigns each record a           scales), but some have colors (65,536). PDAs with color
unique ID number and notes the date it was created. (A record is        screens need more memory and tend to be more expensive.
one appointment, one contact, one memo, etc.) When you press         * Pixel resolution - PDAs have various pixel resolutions
a button on the PDA or its cradle, the sync software compares          (160x160, 240x320). The higher the resolution, the clearer the
the record on the PDA to the one stored on your PC and accepts          display.
the most recent one.                                                 * Passive or active matrix - active matrix displays have
                                                                        sharper images and are easier to read, but tend to be more
The beauty of synchronization is you always have a copy of             expensive
your data, which can be a lifesaver if your PDA is broken or         * Reflective or backlit - backlit screens are good for low level
stolen or simply runs out of power.                                     room lighting conditions
                          Features                                   * Size - Hand-held PDAs tend to have larger screens. Most
                                                                       palm-sized PDAs have four-inch (10 cm) square screens.
Personal digital assistants (PDAs) are one of the fastest selling    * Writing area - Some PDAs only allow you to write in special
consumer devices in history. That popularity means that there are       areas of the screen, while others allow you to write anywhere
many models to choose from. You should first ask yourself
“What do I need my PDA for?” and “How much can I afford to                                       Memory
spend on a PDA?” The answers to these questions will help you        All PDAs use solid-state memory, usually Flash memory; some
find the right model.                                                are even incorporating removable forms of memory. PDAs
                              Size                                   usually come with 2 MB minimum of memory. One megabyte of
                                                                     memory can store up to 4000 addresses and 100 e-mail messages.
Do you want a PDA that you can carry in your briefcase or in         However, many application programs take up memory space, so
your pocket? PDAs come in hand-held or palm-sized models. The        higher models of PDAs usually have more memory (5 to 32 MB).
hand-held computers tend to be larger than the palm-sized. Most,     Also, PocketPC takes more memory space, so PDAs with this
but not all, palm-sized PDAs can fit into a shirt pocket. Also,      operating system usually have 16 or 32 MB. In some PDA
PDAs vary in their weight from 4 to 8 ounces (113 to 227 grams).     models, the amount of memory is upgradeable.
                   Type of Data Entry                                                        Power Supply
Which type of data entry do you prefer? Most hand-held PDAs          PDAs are powered by batteries. Some models use alkaline (AAA)
use a miniature keyboard for data entry. Often the keyboards are     batteries, while others use rechargeable batteries (lithium, nickel-
too small for easy or comfortable typing. In contrast, palm-sized    cadmium, nickel-metal hydride). The battery life depends upon
PDAs use a stylus/touch-screen technology in combination with        the following:
                                                              Page 133
* operating system - PocketPC requires more power by virtue of       receiving IR sensor!). Some PDAs also offer wireless methods to
  its increased memory requirements                                  transfer data to and from a PC/PC network through a wireless e-
* amount of memory                                                   mail Internet service provider like those available on new models
* color LCD displays                                                 of cell phones. Finally, some PDAs offer telephone modem
* special features (voice recording, MP3 player, wireless connec-    accessories to transfer files to and from a PC/PC network. Check
   tions)                                                            the model to see if any of these features are standard or require
                                                                     extra devices.
Therefore, battery life can vary from two hours to two month,s
depending upon the PDA model and its features. Most PDAs                                  Special Features
have power management systems in place to extend the battery
                                                                     Some PDAs have special features such as:
life. Even if the batteries are so low you can no longer turn the
machine back on (it will give you plenty of warning before this      * E-mail * Word processing * MP3 music files * Video games
happens), there’s usually enough power to keep the RAM               * MPEG movie files * Wireless Internet * Video games
refreshed. If the batteries do run completely out of juice, or you   * GPS receiver
take them out of the machine, you’ll have about a minute to                                    Software
replace them before the transistors inside the device lose their
charge. PDAs also come with AC adapters to run off household         All PDAs come with some kind of personal information manage-
electric current. In some models, an AC adapter is not included,     ment (PIM) software for the following tasks:
but rather is sold separately.                                       * store contact information (names, addresses, phone numbers,
                                                                     e-mail addresses)
                       Communication                                 * make task or to-do lists
Because PDAs are designed to work in tandem with your                * take notes
desktop or laptop, they need to work with the same information       * write memos
in both places. If you make an appointment on your PC, you need      * keep track of appointments (date book, calendar)
to transfer it to your PDA; if you jot down a phone number on        * remind you of appointments (clock, alarm functions)
your PDA you’ll want to upload it later to your PC. So, any PDA      * plan projects
must be able to communicate with a PC. The communication             * do calculations
between PDA and PC is referred to as “data synchronization” or       * keep track of expenses
“syncing.” This is typically done through a serial or USB port on    However, not all of these functions are included in every
the PDA. Some PDAs have a “cradle” that they sit in while            package, so check this before you buy. Also, make sure that your
hooked up to the PC. This feature is typically standard on all       PC has similar software so that you can easily exchange informa-
PDAs with the only choice being serial or USB port.                  tion between your PDA and PC. Sometimes, PC PIM software is
In addition to communicating through a cable, many PDAs have         included with the PDA software. Additional specialty software
an infra-red communications port that uses infra-red (IR) light to   may also be available, including maps, video games, and photo
beam information to another PDA or PC (the PC must have a            editing software.

                                 Here’s Wishing You a Good Boot

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