Kinds of computers

Computers vary widely in size, speed, and ability. The size of a computer partly determines the kinds and number of jobs it can do. But even a small computer can perform complicated tasks. For example, a modern desktop computer has more computing power than the huge, room-filling computers of the early 1960's.

The microprocessor--an electronic device consisting of thousands of transistors and related circuitry on a silicon chip--plays an important role in almost all modern computers. A single microprocessor has the computing power of a larger computer but generally costs far less. The small size and relatively low cost of microprocessors have made them valuable as components in computer systems.

Digital computers may be grouped into three categories: (1) embedded computers, (2) personal computers and workstations, and (3) mainframes. The borders between these categories change constantly as smaller, more powerful computers are developed.

Embedded computers control the operation of various types of machinery. Virtually all embedded computers are microprocessors. Such machines as cars, digital wristwatches, telephones, and videotape recorders contain embedded computers.

Personal computers and workstations are computers used by one person at a time. Such a computer usually fits on a desk top, and some personal computers can be held on the lap or in the hands. People commonly use personal computers for such activities as word processing, storing and updating information, performing simple calculations, and playing computer games. These computers also are valuable to business people, who use them to manage information about their inventories, sales figures, customers, and employees.

Personal computers contain one or more microprocessors. By modern standards of computer speed and capacity, personal computers execute programs slowly and have limited memory and file storage capacity.

Workstations are more powerful than personal computers, and better suited to solving difficult engineering, graphics, or scientific problems. Workstations are generally connected to form computer networks. These networks allow operators to exchange information very rapidly. They also enable printers and file storage devices to be shared by many workstations. One important type of computer network, the local area network (LAN), connects workstations located within the same building or in neighbouring buildings. A wide area network (WAN) links workstations over large areas.

Mainframes are fast computers with large memories and file storage systems. These powerful computers solve very complicated problems and manage huge quantities of information. Most mainframes are housed in several large cabinets. Some mainframes do a single job, such as copying and storing the information generated by a laboratory experiment. Others perform many different tasks. Minicomputers and superminis have many of the capabilities of mainframes, but they are smaller and less expensive.

On a large mainframe, hundreds of people may be logged on (running programs) at one time. The use of a single powerful computer by many users at once is called time-sharing. The mainframe appears to run many programs at the same time. However, the computer actually switches rapidly from program to program, doing a bit of work on one and then hurrying on to work on another.

The fastest mainframes are called supercomputers. Supercomputers solve numerical problems as quickly as possible based on existing technology. They are used to model weather systems, to design cars and aircraft, and in many other ways. But supercomputers are rare, because they are extremely expensive. Individual supercomputer users--mostly scientists and engineers at large scientific installations--sometimes run programs by means of long-distance computer networks.

In recent years, mainframes known as parallel computers have provided great increases in speed over other computers. Most computers have a single processor. But a parallel computer has many processors that all operate at once. Each processor can work on a separate piece of a program. As a result, the program can be run much more quickly than on a computer with only one processor. The fastest supercomputers in the world are parallel computers. But parallel computers may even serve as especially fast workstations.

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