Computers have been classified in various ways by type, purpose and size.
Types of computers are based on their mode of operations. Based on these are three types of computers: Digital,Analog and Hybrid computers.
(i) DIGITAL COMPUTER operates on discrete data either alphabets (A-Z) or numerals. Their outputs are quantities that can be discreetly represented. They are used in large business places because of high speed and large internal storage capacity. They range from small sized pocket calculator to giant super computers.
(ii) ANALOG COMPUTER operates by measuring the continuous change in a physical quantity e.g. a thermometer measures temperature while speedometer measures speed etc. the output from an analog computer is often in form of smooth graphs from which information can be read.
(iii) HYBRID COMPUTERS combine the features of digital and analog computers. Hybrid computers are used in research and in application such as process control.
Under this classification we have special purpose computers and general-purpose computers.
SPECIAL PURPOSE COMPUTERS
(i) A special purpose computer is specially designed to process one or more specific applications some of these computers are so specialized that part or all of their operating institution are built into their electronic circuitry. Examples include missiles, airline reservation systems, and stand-alone word processing systems.
(ii) GENERAL-PURPOSE COMPUTERS are designed to process wide variety of applications. The variety of applications that can be processed in limited only by the capacity of the computer.
In the early stages of computer development, the capacity (speed, processing capabilities and cost) of computers was measured in term of physical size. This is no longer so, as development in the electronic field has led To compactness of machines produced. Under this classification we have microcomputers, minicomputers, mainframe and supercomputers.
The microcomputers are also referred to as personal computers or micros. They are small in size; some are as small as a briefcase. Under the micros we have laptops, desktops and tower top computers. Microcomputers are powerful computers. Some are so powerful that they can handle multi users (more than one person using the computer system at the same time). They are not quite expensive compared to minis and mainframes. They are in homes, schools and business organizations.
Tower Top Computer
Minicomputers moderate-size computers. More expensive than most microcomputers. They can handle large number of terminals connected to them. This means that they can support a number of users performing different tasks.
(ii) MAINFRAME COMPUTERS
Mainframe computers are large and powerful computers with fast processing speed that can handle numerous users and store large amounts of data. They are very expensive. Mainframe computers have many users who may be spread over a wide area. Microcomputers can be connected to mainframe computers.
They are the most powerful computers and most expensive. They are able to process hundreds of millions of institutions per second. They are used for such applications as weather forecasting, space exploration and other jobs requiring long, complex calculations.