Tuesday, March 19, 2013



There are many different ways of organizing a computer system. Anyone designing a system has to decide on:

1 The hardware-computers, storage, input and output devices.

2 Communications- between computers and between terminals and computers.

3 The operating system-this very important software organizes the running of the computer system .

4 Other software-this includes utilities, languages and applications programs.

Real-time Processing

A real-time system is one which processes data without significant delay.


1 The computer is waiting for input. As soon as the data is received it is processed, and results can be output straight away.

2 Because the output can be produced quickly it may be used to influence the input. For example, if a computer oversteers a spaceship (example 5 below) it can be adjusted back before any harm is done.

3 The computer is usually running the same program all the time. In fact the computer is often dedicated to the real-time application.

A dedicated processor is one which is working on a particular application and on nothing else. It just runs the same program all the time.

Examples of real-time systems

1 An analogue computer .

2 A machine controlled by a computer, e.g. a 'robot' used in car manufacture.

3 A network controlled by a computer, e.g. the pipelines and pumping stations owned by a Gas Board. The controlling computer communicates with the stations by microwave transmissions at regular intervals, and pressures are adjusted when necessary. (See Fig 1)

4 An interactive game where the user has to react to what is happening on a computer screen by pressing keys quickly.

5 A computer controlling a space flight.

6 An airline flight-booking system.

Advantages and disadvantages of real-time processing


fast response. Output from the computer may be used to adjust and improve the input.


A computer being used for a real-time application often cannot be used for anything else.

Single-User Systems-Microcomputers

A single-user system is one where only one person can use the computer at a time, interacting directly with its operating system to run programs. Microcomputers are usually used in this way. A typical system would have a keyboard, a screen, a floppy disc unit and a character printer.

Examples of the use of a microcomputer as a single-user system

1 As a 'home' computer.

2 In a neweagent's shop to store details of the newspapers required by customers, to organize the newspaper rounds and to work out customers' accounts.

3 In an office as a word processor .


Fig 1 A typical single-user system based on a microcomputer

Advantages and disadvantages of single-user systems


1 Inexpensive-cheap enough to be used:

(a) As a home computer.

(b) By a small business.

(c) In schools for teaching and administration purposes.

(d) Dedicated to one application, such as process control or word-processing.

2 The user bas better control over:

(a) The uses to which the computer is put.

(b) What changes are made to the system.

(c) Security.

(d) Maintenance.

3 Mobile and small-a microcomputer can be:

(a) Moved from place to place.

(b) Attached to equipment in order to control it.

4 Robust and reliable-microcomputers can function in more variable conditions than larger computers.


In comparison with a mainframe computer a single-user system often has:

1 Slower processing.

2 Less storage.

3 Fewer and slower peripherals.

4 Less sophisticated software.

These disadvantages can be partly overcome if the single-user system is able to communicate with larger systems. For example, it may be used as a workstation in a network .