This Unit is of Classification of computers.

In the previous unit, we looked at Analog, Digital and Hybrid as the categories of computers basing on how they represent data.

Those categories of computers are sometimes referred to as classifications of computers by process or by nature.

In this unit, we are going to further classify digital computers according to their size, their purposes, functions and processing power.


According to size or capacity, we base on the physical size and the number of people the computers can accommodate at the same time.

Digital computers can be grouped into four classes as follows:

Super Computers

Super Computers are the best in terms of processing capacity.

These computers can process billions of instructions per second.

They are used for applications which require intensive numerical computations such as weather forecasting.

They have a high storage capacity and are huge in size. They generate large amounts of heat and therefore need complex cooling systems.

A supercomputer channels all its power into executing a few programs as fast as possible. Super computers are the most expensive ones

Supercomputers like the Cray T90 system has thousands of processors. Supercomputers cost very high and are therefore only used by large corporations, government agencies and universities that can afford them. Because of their extraordinary speed, accuracy and processing power, supercomputers are well suited for solving highly complex problems and performing tasks that demand huge amounts of calculations.

The following functions are some of those performed by supercomputers: space exploration and sending of astronauts into space; controlling missile guidance systems and satellites for national defense; oil exploration; hosting extremely complex web sites and decision support systems for organizations; etc.


Mainframe Computers (also known as big iron)

These are powerful computers used mainly by large organizations for bulk data processing such as census, and financial transaction processing.

They are also called central processors because they process data centrally.

These computers are used in places where processing needs to be done in bulk such as banks.

They can store a lot of information

They support a wide range of peripheral devices

They have many users connected via dumb terminals.

What are Dumb Terminals?

Dumb terminals are display and input devices which don’t process data, instead they transmit input to a computer to which it is connected and display the resulting output.

Dumb terminals have no ‘intelligence’ (data processing power) and depend entirely on the (intelligent) computer to which they are connected for computations, data storage, and retrieval.


Mini Computers (a.k.a. mid range computers)

A minicomputer is a class of multi-user computers that lies in the middle range between mainframe computers and the smallest single-user systems (microcomputers or personal computers).

They are similar to main frames but they are smaller in size, support a limited number of peripheral devices connected to them, Have a lower speed, have lesser storage capacity, and support fewer number of users at the same time than as compared to main frames.

A microcomputer is a computer with a microprocessor as its central processing unit.

When equipped with a keyboard and screen for input and output, they are also personal computers.

They are single user and are the most widely used computers in our everyday life.

Micro computers are relatively cheap, smaller in size and support fewer peripheral devices.

Micro computers are further classified into:

a) Desktop computers: Designed to be stationed in one place probably on top of a desk.

b) Laptop computers: These are more portable and suitable for mobile computing.

c)  Palmtops/Personal Digital Assistants (PDAs): These are handheld digital computers



According to Purpose, we base on the variety of problems that a computer can help to solve.

Computers can be grouped into two classes as follows:

Special Purpose Computers

A special purpose computer is designed to operate on a restricted type of problems.

They have instructions permanently stored in them to perform the given task quickly and efficiently.

Most special purpose computers have the capability of performing just one task.

They are commonly referred to as “dedicated computers,”

Examples of Special Purpose Computers

  • Automatic Teller Machines (ATM),
  • Pocket calculators,
  • Computers that operate lifts.

NB: Most analog computers are special purpose computers.

General Purpose Computers

General-Purpose Computers are designed to solve a wide range of problems.

They are also able to act in response to new programs created to meet different needs.

A general-purpose computer is one that has the ability to store different programs of instruction and thus to perform a variety of operations.

Most PCs (Desktops, laptops and palmtops) are general purpose.


According to Function, we base on what computers do and how they do it.

We have four classifications of computers by function:

i. Networked

ii. Stand-alone

iii. Real-time Systems

iv. Integrated Systems

Networked computers

These are computers connected by channels to other computes so that they can communicate with each other and share resources like data, internet connection, printers, etc.

Stand-alone computers

This is a computer that operates and does everything independently.

Stand-alone computers do not have any internet connection or a connection to the outside world.

A photocopying machine is a stand-alone device because it does not require a computer, printer, modem, or other device.

A printer, on the other hand, is not a stand-alone device because it requires a computer to feed it data.

Real-time systems

These are systems that respond to an event that has occurred within a certain specified time frame.

Real-time means that after an event has occurred, a system or application has to react to that event within a certain time period or deadline.

For example, computers for a banking system are real time systems.

Integrated system

An integrated system is a group of interconnected units that form a functioning computer system.

An integrated system has separate programs that perform separate functions but they all contribute to the same output.

Boeing Integrated Defense Computer System (1995)


PCs can be classified by their microprocessor model name or number.

The leading processor chip manufacturers for personal computers are Intel, AMD, IBM, and Motorola.

Due to the rapid changes in technology processing power is also rapidly increasing. Computers are getting faster and faster each time a new micro processor chip is introduced .

Examples of Microprocessors

The most common types of processor power are:-

  • 80286
  • 80386
  • Pentium I
  • Pentium II
  • Pentium III
  • Pentium IV
  • Pentium Duo core,
  • Core 2 Quad,
  • Celeron,
  • Celeron D,
  • Xeon,
  • Opteron,
  • Athlon,
  • Itanium

The unit for measuring the processing power is the Hertz.

For example, Celeron processors’ speed ranges from 266MHz – 2.8 GHz.


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