Classification of Computers – SS1 Data Processing Lesson Note (First Term)

Computers are classified in three ways: by type (digital, analogue or hybrid), by purpose (general-purpose or special-purpose) and by size (supercomputers, mainframe computers, minicomputers and microcomputers). Each class groups computers by how they process data, the problems they solve, or how large, fast and costly they are.

Behavioural objectives

By the end of the lesson, students should be able to:

• name the three types of computer and give an example of each;
• distinguish between general-purpose and special-purpose computers;
• list the four classes of computer by size;
• describe the features of supercomputers, mainframes, minicomputers and microcomputers;
• state reasons why microcomputers are widely used.

How are computers classified by type?

Computers can be classified by type into three major types:

1. Digital computer
2. Analogue computer
3. Hybrid computer

Digital computer

This is the most common type of computer today. It measures physical quantities by counting. Examples are calculators, digital wristwatches and digital fuel dispensers.

Analogue computer

This type of computer is used to measure and process continuous data such as speed, temperature and heartbeat. Examples are speedometers and thermometers.

Hybrid computer

This type of computer combines the features of digital and analogue computers.

How are computers classified by functionality?

Classified according to purpose, computers fall into two groups:

1. General-purpose computers
2. Special-purpose computers

General-purpose computers

These are computers designed to solve a vast variety of problems. For example, they can be used for word processing and, at the same time, for graphics, databases and spreadsheets.

Special-purpose computers

These are computers designed solely to solve a restricted class of problems, for example computers for medical diagnosis, weapon guidance, traffic control, and weather study and forecasting.

How are computers classified by size?

Computers can generally be categorised into four classes:

1. Supercomputers
2. Mainframe computers
3. Minicomputers
4. Microcomputers

Supercomputers

These are the largest, fastest and most expensive computers. The cost is several millions of dollars and the speed is between 600 million and 900 million instructions per second (MIPS).

Another name for a supercomputer is MONSTER. Scientists use supercomputers in weather forecasting and similar scientific work. They can also be used for complex calculations. An example is the CRAY X-MP.

Mainframe computers

A mainframe computer is a large computer in terms of price, size of internal memory and speed. It has more peripheral devices, such as printers and plotters, than are found with small computers, except small computers with large amounts of external storage.

Mainframe computers usually need a specialised environment to operate, with dust, temperature and humidity carefully controlled. They are used in large establishments such as banks and airports. Examples of mainframe computers are the IBM 360/370 and NCR-V 8800.

Minicomputers

Minicomputers were developed in the 1970s for specialised tasks (that is, they are special-purpose computers). They are smaller, less powerful and less expensive than mainframes.

Minicomputers are easier to install and operate. Examples are the PDP-11, VAX 750/6000, NCR 9300, DEC and HP 3000.

Microcomputers

A microcomputer is a computer whose central processing unit (CPU) is based on a microprocessor.

Microcomputers are at present the most popular computers. They are very small and easy to use. Their capabilities are generally fewer and less complex than those of minicomputers or mainframe computers. Another name for a microcomputer is Personal Computer (PC).

Why are microcomputers widely used?

1. They are cheap.
2. They are small.
3. They do not require a special environment to operate.
4. They can be used anywhere.

Evaluation

1. Name the three types of computer by type and give one example of each.
2. What is the difference between a general-purpose computer and a special-purpose computer?
3. List the four classes of computer by size.
4. Why do mainframe computers need a specialised environment?
5. State three reasons why microcomputers are widely used.

Assignment

1. Describe a supercomputer and state one way it is used.
2. Differentiate between a minicomputer and a mainframe computer.