CH / S4CS / Nov. 2002
A Typical Computer System
CPU
control unit
Arithmetic and
Logic Unit (ALU)
Input
Device
Main memory

Output
Device
Secondary
storage
Input device. The mechanical unit which accepts data into a computer.
E.g.

Output device. The unit from which data and information come out of the computer.
E.g.

Central Processing Unit (CPU). The main part of a computer responsible for all the processing of
data. It can be roughly divided into two parts:

i.
Control Unit (CU). Part of the CPU which directs operation.
ii.
Arithmetic and Logic Unit (ALU). Part of the CPU which performs the arithmetic and logic operation.
Main Memory. The part of the computer responsible for storing up the program and data temporarily
during processing.

Secondary Storage. The entities used to store the program and data permanently.
E.g.
Program and Data

Program. It is the set of instructions that tells the computer how to do its work.

Data. It is a collection of raw, unprocessed facts that are input into a computer system.

In data processing, computer programs are used to process data into information.
Hardware and Software

Hardware. It refers to the physical components of a computer system. A basic computer system has the
hardware components as stated in the above section.

Software. It is another name for computer programs. There are two kinds of software
i.
Applications software.
a.
It is the end-user software that we use for everyday work.
b.
E.g. word processing system, electronic spreadsheets and presentation graphics package, school
report card printing program, etc.
COMPUTER BASICS
page 1
CH / S4CS / Nov. 2002
ii.
c.
An application software can be:

Packaged software. It is a general-purpose program pre-written by professional programmers.
E.g. MS Office.

Custom-made software. It is a program written to meet the specific requirement of an
organisation. The organisation may hire computer programmers or hire service from software
houses to write the programs to perform the specific task like payroll system or customer service
system.
System software.
a.
It is supplied by computer manufacturer and software suppliers.
b.
It raises efficiency and process capability.
c.
E.g. All compilers, interpreters, assemblers and operating systems.
d.
It makes a computer more useful and easy-to-use.
Classification of computer systems

Computers are classified by their physical size and computing capability such as processing speed and
memory size.

Microcomputers. (1 user) They are also known as
(
) and used for
general purpose. They can desktops, notebook PCs and palmtops.

Minicomputers. (10 users) Ten or more users use a same system unit together through their terminals.
They link users in the same office or laboratory together.

Mainframe. (100 users) They are room-size systems capable of high speed processing of large amounts
of data for many users at the same time. Under such a system, a hundred of users in a large organisation
such universities and banks can share the same system unit together.

Supercomputer. They are high-speed special purpose computer systems. They are built to process large
amounts of mathematical and scientific data for applications such as world-wide weather forecasting and
space exploration research.
COMPUTER BASICS
page 2