A mainframe computer is the largest, fastest and perhaps one of the most expensive computer systems of general use. Before the advent of minicomputers and microcomputers respectively in the third-and fourth-generation periods, all data processing was done on mainframe systems only. Thousands of such machines are still in use in medium-and large-size business houses, universities, hospitals, etc. These machines have a very large primary storage capability and have a very high processing speed. Because of their size and speed, mainframe systems must be placed on special platforms that allow wiring and cooling systems. These machines are useful not only because they have an enormous storage capacity but also because of their capability to support a large number of terminals. Modern-day mainframe computers are defined by their high-quality internal engineering, reliability, technical support and security features, along with their performance qualities. Their applications include the processing of a huge amount of different kinds of data such as census, industry/consumer statistics, financial transactions processing, etc., in large private and public enterprises, government agencies, etc. Examples of mainframe computers include IBM’s zSeries and System z9 servers, Unisys’s ClearPath mainframes, the zSeries 800 from Hitachi and IBM, the Nonstop systems from HP and so on.

A minicomputer more or less resembles a mainframe system except that it is comparatively smaller and less expensive. They represent a class of multi-user computers that are used for middle-range computing applications, in between the mainframe systems and the microcomputers. Minicomputers were developed during the third-generation period. PDP-8 and PDP-11 from Digital Equipment Corporation (DEC) are examples of the popular minicomputers developed in the late 1960s. Minicomputers gave way to microcomputers in the mid-1980s and early 1990s.

The microcomputer, the development of which was made possible largely owing to the development of the microprocessor, is a compact, relatively inexpensive and complete computer. The most obvious, though not the only difference between a microcomputer and a mainframe is the physical size. While a mainframe system may fill a room, a microcomputer may be put on a desktop or may even fit into a briefcase. Although microcomputers can be distinguished from mainframe and minicomputers on the basis of size, technology used, applications and so on, these dividing lines are hazy and these categories almost overlap with each other owing to brisk advances in technology. Like mainframes and minis, today’s microcomputers do data processing, manipulate lists, store, retrieve and sort information. Unlike mainframes and minis, microcomputers do not require any specialized environment for operation and can be effectively made use of by people who do not have any comprehensive formal training in computer techniques. In fact, these machines are designed to be used both at the workplace and at home. The concept of office automation has become feasible only with the advent of microcomputers.

The text for supercomputers was not provided in the original content, but typically, supercomputers are known as the most powerful type of computer, designed to perform at the highest capacity. They are used for tasks that require intense computational power, such as scientific simulations or weather forecasting.