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
Getting To Know Your Computer
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?
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
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.
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.
Steps to produce a document Typeface - set of characters of similar design like:
* Create Century Gothic
* 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
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
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
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
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.
Print Preview shows you how it will look in print
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
* 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.
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
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
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
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
* 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,
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.
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
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
* 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
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
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
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.
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)
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
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
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.
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
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
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 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.
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
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!
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.
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
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,
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
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?”
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
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
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
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!!
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.
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
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
* 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,
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
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.
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
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.
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!!
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??
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.
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
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!
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,
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
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
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
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)
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
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
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.
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
Types of Digital Modems
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.
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
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
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.
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
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.
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
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
* 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:
* 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.
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.
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
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.
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
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.
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.
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!
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
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
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
Pentium II 1997 7,500,000 0.35 233 MHz 32 bits ~300
Pentium 3 1999 9,500,000 0.25 450 MHz 32 bits ~510
Pentium 4 2000 42,000,000 0.18 1.5 GHz 32 bits ~1700
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
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-
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.
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-
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
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
* 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.
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.
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
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
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.
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
* 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.
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.
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
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.
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
For Mouse and
Chipset Battery Storage Device Connectors
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
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.
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
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
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
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
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.
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 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.
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
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
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
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.
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.
* 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
* 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
* 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
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
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
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
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
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
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
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.
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
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
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.
* 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
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
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
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.
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
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
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
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 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.
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
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
* 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.
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
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.
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.
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.
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.
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 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
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
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.
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
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.
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.
Most mice in use today use the standard PS/2 type connector, as
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)
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
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-
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.
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
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
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.
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.
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
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.
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
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,
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
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
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
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”
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
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!
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 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.
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.
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.
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
allow for error correction — this information is really just a
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
* 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 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
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.
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
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.
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/
24-bit DAC required to play these audio discs.
Remote-control type DVD players may come with three types
* 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
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.
* 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.
* 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.
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.
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.
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.
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.
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
9600 bps - First appeared in late 1990 and early 1991
19.2 kilobits per second (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.
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.
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
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
* 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
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).
* 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
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
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
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.
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
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.
* 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
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
* 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
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
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 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
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.
over-molded thin package (OMTP). This allows everything to be
integrated into a single package without the need for soldering.
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.
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.
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.
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
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
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
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-
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.
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
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.
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
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
Memory * If there are two sounds playing simultaneously, we can only
hear the louder one.
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
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?
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
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.
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-
* Users run a piece of Gnutella software to connect to the
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
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.
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.
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.
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
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
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
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
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.
* 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
* 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
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!
Good Boot Guide to Your
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
* 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-
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
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.
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.
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
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.
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:
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.
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
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
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.
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.
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
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
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
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
* 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
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
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).
* 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.
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
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).
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.
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
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
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
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.
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
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.
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
* 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
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
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
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.
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.
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
* 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.
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
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-
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
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:
* 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
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,
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