hardware by qingyunliuliu


                 Or: How to Buy a Computer
        The first step in digitally developing labour organizations is, obviously, to ensure that they
have computer equipment. This equipment can be purchased by the union itself or by a funding
body. Either way, people in the union have to understand how a computer and its related equipment
is purchased. That's what this section is about : how to go to a computer store and buy a computer
without getting lost in all the jargon.

      A microcomputer consists of four major components. You will have to know about each of
them when you talk to the salespeople.



       Input/output devices


        We will look at each of these in turn. Don't worry if you don't understand all the stuff we'll
discuss here on the first reading. Read the document a second time. Ask questions in the computer
conference related to this module. Most people find it easier to print the document so they can read
it as hard copy (printed).

CPU - the Central Processing Unit

      The first question you will have to consider when buying a computer is what sort
microprocessor you want. "Microprocessor" is another name for the Central Processing Unit of the
computer, the CPU.

      When the microcomputer was first introduced the microprocessor was referred to by
numbers such as : 286, 386, 486. Today they are given names such as Pentium and Athlon.

       A Pentium 4 microprocessor (which is produced by a company called Intel) is equivalent to
the Athlon microprocessor (created by another company called AMD).

        What makes the difference between current microprocessors is the speed at which they
execute instructions. This speed is determined by an internal clock. How fast this clock pulsates
(tick-tock, tick-tock) is measured in hertz. You don't have to understand what a hertz is. All you
have to know is that a microprocessor working at 8MHz (8 MegaHertz) is much s lower than one
which operates at 3 GHz (3 GigaHertz). And, you get what you pay for : the faster the
microprocessor the more you'll have to pay. The difference between Mega (smaller or less ) and
Giga (bigger or more ) will be explained later in this document.


      The second component you will have to know about when talking to people about buying
computers is memory. Don't forget!
       Memory is divided into two main types : RAM and ROM. They both involve pieces of
hardware which are plugged into the computer's main box ( the system or base unit).

        RAM is Random Access Memory. It is the computer's main memory. The more of it you
have, the faster your programs will run. That's because the computer uses its RAM to hold data,
pieces of the operating system (such as Windows or Linux) and parts of the programs you are
working with. If the RAM gets filled up, the computer runs more slowly. If you run many
programs (multitasking) the RAM will get more full and things will start going very
s _ l_ o_ w_ l_ y.

       RAM is known as volatile memory. That means it is available only when the computer is
turned on. If you have data in RAM, and you turn off the computer, that data will be lost, forever.
Arrrrggghhhh!!! So make sure you save the data as you go along.

       One way of protecting a computer from electrical stoppages which cancel RAM is to plug
the computer into a battery- like thing called a UPS - an Uninterruptible Power Supply. The UPS
holds enough power to give you a chance to save your files and safely shut down the computer.

      ROM is Read Only Memory. It's the permanent memory which is not lost when the
computer is turned off. It us used for starting ("booting up") the computer. YOu do not have to
know what ROM is. All you have to know is that it exists.

         When people talk about the amount of memory a computer has they are referring to its

Memory Size

      More memory in a computer is better than less memory. Which means it's important to
measure the amount of RAM that is in, or can be put into, a computer.

        It all starts with bits and bytes. A bit is a 0 or a 1. A place in the memory either has an
electrical charge ( 1 ) or it doesn't ( 0) . A byte is a collection of bits - eight bits to be exact : for
example 10110010.

       Bytes are important because one byte represents one charactor: M, ?, 5, (including the
commas) are all represented by one byte of memory. Here's what a capital "A" looks like to a
computer: 01100101. Spaces also take up a byte of memory because they are treated like real

         The measurement system used to talk about computer stuff is metric. Here are the basic

         kilo           one thousand            KB
         mega           one million             MB
         giga           one billion             GB

      RAM is measured in megabytes (MBs). Most new computers have between 128MB and
256MB. But you can put more memory into a computer (by adding chips or cards inside the
       Let's say you have a computer with the minimum 128 MB of RAM; you are using Windows
98; and you are running a number of programs. Here is the memory space the programs could take:

       Windows                                takes 32 MB
       Microsoft Word or OpenOffice                 40 MB.
       Internet Explorer or Firefox                 20 MB.

         That leaves you only 36MB for data or other programs. That's not much. The more memory
that is being used, the slower your computer will operate. The solution is to add more memory (or
buy more when you first purchase the computer). You should have at least 256MB in a new

Input devices

        Input devices are pieces of hardware which are used to put data into a computer. They
include keyboards, a mouse, microphones, digital cameras, bar codes a nd scanners. Bar codes are
those thin black marks you see on supermarket products. A bar code readers translate the marks
into data such as product prices.

       A scanner is a piece of equipment which can be used to put text, pictures and grapics into
the computer. Text that is scanned is a picture of text on the page. It can't be edited. But if you use
OCR (optical character recognition) software you can edit the text just as would a word processing

Output devices

       Output devices are things like monitors, printers, and speakers.

       There are two types of monitors in use today : Cathode Ray Tubes (CRT) and Liquid Crystal
Display (LCD). CRTs contain electronic guns which shoot electrons at phospher dots painted on the
back of the screen. The dots light up in different combinations (such as letters) when they are hit
with the electrons. LCDs have liquids in them which reflect light differently when electric voltages
are applied.

    Monitors are measured diagonally from the top left corner of the screen to the bottom right.
Common sizes are 15 ", 17" , 19" and 21". Bigger costs more.

        Printers can be divided two types: impact (which means "to hit") and non- impact. Impact
printers have ribbons which have ink on them that is pressed to the paper by a de vice inside the
printer. A dot matrix printer, for example, has a square of little pins which extend in different
combinations to hit the ribbon and create characters or pictures.

        Non-impact printers include laser printers and ink-jet printers. Laser printers work like
photocopiers: fine powder is attracted to paper in different combinations by electric charges. Ink-jet
printers spray fast-drying ink on to the paper.

Storage devices

        Even though RAM is known as primary or main storage you can't keep data in RAM for
long. Eventually the computer will shut down and everything in RAM will be lost. The data has to
be put into more permanent storage such as disks. Disks are a sort of secondary storage.
Hard disks

        Hard disks are the things on which most computer data is stored. They are usually built into
the computer box ( the system unit). The computer takes part of programs from the hard disk and
puts them into RAM so they can be used quickly. Hard disks are much slower to access (use) than

       Some programs, such as Windows, create temporary files on hard disks while the programs
are running and delete them when the program is closed.

Floppy disks

       Long ago computers used to store data on big 8" squares of magnetic tape sandwiched
between light cardboard. They were so soft that they could flop around; so they were called

       Today floppy disks are encased in 3.5" squares of hard plastic. You can still see the tape if
you move the metal door (which is what the computer does when it wants to read the data on the

        Floppy disks are still used a lot these days becasue they are portable and great for moving
data from one computer to another. They hold about one and a half megabytes of data (1.44 MB)

Compact Disks (CDs)

      One and half megabytes (1.44) is not very much space. You couldn't, for instance, put a
program like OpenOffice on it. So people use CDs because they can hold much more. A typical
CD can hold 700 MB - that almost 500 floppy disks!

       It used to be that CDs were called CD-ROMS because, after they were given the first data,
they could not be used to add more data. They were Read Only.

       Today, there are CDs which can be written on to many times. They're called rewritable

       CDs are much faster than floppy disks. The speed you see written on a CD refers to how fast
they can be used for recording music.

Digital Versatle Disks (DVDs)

        DVDs are just CDs which can hold much more data. Some store as much as 17 GB of data.
That's a lot of space; enough to hold a whole movie. You need a special hard drive to read a DVD
because DVDs are read by two little lasers in the the computer. Ordinary CDs can be read with just
one laser.

Disk Costs
       The cheapest disk is the floppy. They come in boxes of ten. CDs are more expensive than
floppies. DVDs are a little more expensive than CDs.

       Hard disks are the most more expensive, but they are becoming much less expensive
becauses they are being designed to hold more data. They are priced according to how many
gigabytes of space they can hold.

Formatting disks

       Most disks come already formatted, which means "to get a disk ready for use".

         The formatting procedure established a series of blocks into which data can be writtten. The
first track of blocks on a disk is like a directory of the disk. This directory is called the FAT (file
allocation table). It tells the computer what blocks are free and can be used to store data. If the FAT
is corrupted (broken) the disk cannot be used.

       If you format a disk all the data on that disk will be deleted.

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