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

Classification of computers is the grouping of computers by type, by purpose and by size.

Behavioural objectives

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

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

What are the ways of classifying computers?

Computers are classified in three ways: by type, by purpose and by size.

• By type: digital, analogue or hybrid, based on how the computer handles data.
• By purpose: general-purpose or special-purpose, based on the problems it is built to solve.
• By size: supercomputer, mainframe, minicomputer or microcomputer, based on size, speed and cost.

How are computers classified by type?

There are three types of computer: digital, analogue and hybrid.

What is a digital computer?

A digital computer is a computer that processes data in discrete form, by counting.

• Data: works with separate numbers and digits.
• Use: it is the most common type of computer today.
• Examples: calculators, digital wristwatches and digital fuel dispensers.

What is an analogue computer?

An analogue computer is a computer that measures and processes continuous data.

• Data: works with quantities that change smoothly, such as speed, temperature and heartbeat.
• Examples: speedometers and thermometers.

What is a hybrid computer?

A hybrid computer is a computer that combines the features of digital and analogue computers.

• How it works: the analogue part measures continuous data and the digital part processes it and shows the result as numbers.
• Example: machines in hospital intensive care units that measure a patient’s heartbeat and temperature and display them as numbers.

What is the difference between digital and analogue computers?

How are computers classified by purpose?

There are two classes of computer by purpose: general-purpose and special-purpose computers.

What is a general-purpose computer?

A general-purpose computer is a computer designed to solve a wide variety of problems.

• Flexibility: it runs different programs, so one machine can do many jobs.
• Example uses: word processing, graphics, databases and spreadsheets on the same computer.

What is a special-purpose computer?

A special-purpose computer is a computer designed to solve only a restricted class of problems.

• Medical diagnosis: computers built to help find illnesses.
• Weapon guidance: computers built to control and aim weapons.
• Traffic control: computers built to run traffic lights.
• Weather study and forecasting: computers built to study and predict weather.

What is the difference between general-purpose and special-purpose computers?

How are computers classified by size?

There are four classes of computer by size: supercomputers, mainframe computers, minicomputers and microcomputers.

What is a supercomputer?

A supercomputer is the largest, fastest and most expensive type of computer.

• Cost: several millions of dollars.
• Speed: extremely high, measured in instructions per second.
• Uses: weather forecasting, other scientific work and complex calculations.
• Example: CRAY X-MP.

What is a mainframe computer?

A mainframe computer is a large computer with high price, large internal memory and high speed.

• Peripherals: it has more peripheral devices, such as printers and plotters, than small computers.
• Environment: it needs a specialised room with dust, temperature and humidity carefully controlled.
• Uses: large establishments such as banks and airports.
• Examples: IBM 360/370 and NCR-V 8800.

What is a minicomputer?

A minicomputer is a computer that is smaller, less powerful and cheaper than a mainframe.

• Origin: developed in the 1970s for specialised tasks.
• Installation: easier to install and operate than a mainframe.
• Examples: PDP-11, VAX 750/6000, NCR 9300 and HP 3000.

What is a microcomputer?

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

• Popularity: at present, the most popular computers.
• Size: very small and easy to use.
• Capability: generally fewer and less complex than those of minicomputers or mainframes.
• Other name: Personal Computer (PC).
• Examples: desktop computers and laptops.

How do the four size classes compare?

Why are microcomputers widely used?

Microcomputers are widely used because they are cheap, small and easy to use anywhere.

1. Cheap: individuals, schools and small businesses can afford them.
2. Small: they fit on a desk or in a bag.
3. No special environment: they work in ordinary rooms and offices.
4. Portable: 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

Describe a supercomputer and state one way it is used. Then draw a table that differentiates a minicomputer from a mainframe computer.