**** COMPUTERS EXPLAINED ****************************************** PAGE ***

A computer is a machine that processes information, or data according
to a set of instructions called a program, like a program of things
to do.  The info and instructions are stored in the computer's memory
until they are needed, and then are carried out by the machines central
processing unit, or CPU.

Hardware are the extra pieces of equipment that you add on to the computer
and the things that make up the computer, like the keyboard and screen.

Software are all the programs which tell the computer what to do.  This
includes programs which are built in to the system, as well as programs you
type in.  Or games loaded in etc.

Peripheral is any extra piece of equipment which you can connect to the
computer.  For example, you can use a cassette recorder or a disk drive to
store programs and information on cassettes and disks.  Other examples of
peripherals are a printer, for printing programs or information on paper,
and aplotter for printing pictures.

Cassettes.  Most cassettes used for storing programs and data are ordinary
audio cassettes - the same kind as you use to record music or voices.  You
can also buy special data cassettes from computer retailers.  These are
spcially designed for recording computer data and programs and have a much
stronger magnetic field and are much more reliable.
A cassette contains a length of magnetic tape on which computer signals are
recorded as areas of varying magnetism.  If you listen to a cassette on
which a program is recorded, you hear the signals as a series of high
pitched bleeps.

More peripherals are:

Digital Tracer
Also known as a digitizer.  It is a special hinged arm which you can use to
trace over drawings and graphs and which sends the information to the
computer for drawing out on the screen.

Mouse
This is a small device with wheels which is used to input data by tracing
over graphs etc. or to indicate a position which an on-screen pointer
should move.

Modem
This stands for modulator/demodulator.  It is a device which allows you to
send and receive computer signals along telephone lines.  It does this by
converting signals into phone signals and vice-versa.  A modem may be built
into a special telephone or it may take the form of an acoustic coupler.

Acoustic Coupler
This is a portable modem.  Often just known as a modem, which can be used to
connect to a computer and any standard telephone.  You place the telephone
handset into the coupler and it converts the signals travelling to or from
the computer.  It has two rubber cups (round) which will attach easily to
most standard round ended hand sets, but you may have trouble with newer
smaller square shaped ones.

Joystick
This is a lever like device that can be moved in any direction to move
things on the screen.  It is used mainly in computer games.  Most joysticks
have a fire button or hit key which sends a "fire" signal to the computer.

Paddle
This is a knob-like device, used like a joystick for moving things,
particularly in bat and ball type games like PONG.

Light pen
This is a pen-like instrument which you connect to a computer and use it to
draw on a screen directly.  Or you can choose an option by pointing to it on
the screen, extrememly useful and easy to use.  Be ready for a big blast of
these in the coming years.

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Disks
Floppy disks, also called flexible disks or diskettes.  These are thin
plastic disks on which computer programs can be stored in a similar manner
to cassettes.  The programs can be read or recorded onto the disk in a disk
drive.

Disk controller.  This tells the computer how to work the disk drive.  It
can be either a small printer circuit board or extra chips.

Disk interface.  This controls the signals travelling between the computer
and the disk drive.

Disk operating system.  Often shortened to DOS (pronounced Doss).  This is a
group of programs which tell the computer how to read and write programs on
the disks.  Some computers have a DOS already in ROM
but others have a short program which knows just enough to load the main DOS
from disk.  This is called BOOTING DOS (Amiga does this).

Types of disks

Floppy disks can be either single sided (ss) or double sided (ds).  Data is
recorded ontro disks as a pattern of magnetic dots and disk density refers
to the amount of data that can be stored on a single disk.

Minifloppies
These are 5¼ inches in diameter and can hold at least 100K, depending on the
density of the disk.  Most micro computers use minifloppy disks.  Usually
they are just called floppy disks.

Microfloppies
These are between 3 and 4 inches in diameter and different makes hold
differet amounts of data.

Standard floppies
These are 8 inches in diameter and are used mainly on large computers.

Hard Disks
These are made of hard non-flexible material.  A typical 5¼" hard disk can
store at least 5 megabytes.  They are used mainly on large computers.


Next disk we look at networks, databases, printers and more!

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