Types of computers

There are many types of computer systems in existence. This section summarises some of the more common types currently available.

PC/desktop computers

PC/desktop usually refers to a general purpose computer which is made up of separate monitor,  keyboard, mouse and processor unit (see Figure 1.1). The term PC (personal computer) usually refers to computer systems which are IBMcompatible, thus distinguishing them from, for example, Macintosh systems.

It is worth making a comparison here with laptop computers:


  • Spare parts and connections tend to be standardised, which usually results in low costs.
  • Desktops tend to have a better specification (e.g. faster processor) for a given price (often due to size and construction constraints in laptops).
  • The large casing allows good dissipation of any heat build-up.


  • Desktops are not particularly portable since they are made up of separate components.
  • All the components need to be hooked up by wiring, which can be quite complex and clutters up the desk space.
  • Because they are not particularly portable, it is necessary to copy files, etc. when you want to do some work elsewhere (e.g. at home).

Laptop computers

Laptop (or notebook) refers to a type of computer where the monitor, keyboard, pointing device and processor are all together in one single unit. This makes them extremely portable systems.
The key features you would expect to find in a laptop are:
  • low weight (to aid portability)
  • low power consumption (and also long battery life)
  • a processor that does not generate too much heat (cooling is very important).


  • They are very portable, since the monitor, pointing device, keyboard, processor and backing store units are all together in one single box.
  • There are no trailing wires, etc. because everything is in one single unit.
  • They can take full advantage of WiFi.
  • Since they are portable, they can link into any multimedia system.


  • Since they are portable, they are easy to steal!
  • They have limited battery life so the user may need to carry a heavy adaptor.
  • The keyboards and pointing devices can sometimes be awkward to use.
  • Heat dissipation is more difficult due to the structure of the laptop computers.


Netbook is a term used to describe a computer that can almost fit onto a hand and is a smaller version of a laptop. These used to be known as palmtop computers, but this term now generally applies to much smaller devices which use touch screens and often a stylus to key in data.


Netbook computers have many of the features of laptops and therefore have similar
advantages and disadvantages.


In addition to the disadvantages listed above for laptops:
  • netbooks don’t have optical drives
  • the keyboards are only about 80 per cent the size of laptop keyboards
  • they lack some of the features found in larger machines, principally due to the size constraints and to the fact that they are cheaper to purchase.

Personal digital assistants

Personal digital assistants (PDAs) are small handheld computers that usually come with a touch screen that is activated using a stylus. Data (e.g. text) is entered by using a keyboard that appears on the touch screen. Originally, these devices were used as personal organisers but their use has expanded somewhat to include new generation mobile phones, data loggers, satellite navigation systems, etc. Many PDAs now have basic database, word-processing and spreadsheet facilities.


  • They can be used anywhere because of their size.
  • They are very lightweight and are more portable than laptop computers.


  • It is difficult to enter text quickly.
  • They have very limited capabilities due to the software and the operating system used.

Mainframe computers

Mainframe computer is a term used for a large, very powerful, computer system.
The name comes from the days when the individual components were housed in
large (often room-sized) frames.


Their main purpose is to run commercial applications, such as banking and insurance, where huge amounts of data need to be processed each day.

The main features of mainframe computers are as follows.
  • They can have several CPUs.
  • They have very fast processor speeds.
  • They can support multiple operating systems.
  • They have huge amounts of storage capacity.
  • They have huge internal memories (e.g. several hundred Gbyte of RAM).
  • They often operate using time sharing or batch processing.


  • Due to the features listed above, they can be used to do very large jobs that require large memories and very fast processor time.
  • They are used in time-sharing systems to allow users to be given a time slice of the very powerful facilities afforded by a mainframe system.
  • They are capable of very large number crunching, and so can deal with very complex mathematical functions (e.g. fractals) which would be very time consuming using, for example, a PC.


  • Mainframe computers need to be permanently housed in a large room, so cannot be moved around.
  • They are very expensive to operate and maintain.
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