Computers are categorized by both size and the number of people who can use them concurrently. Supercomputers are sophisticated machines designed to perform complex calculations at maximum speed; they are used to model very large dynamic systems, such as weather patterns. Mainframes, the largest and most powerful general-purpose systems, are designed to meet the computing needs of a large organization by serving hundreds of computer terminals at the same time. Minicomputers, though somewhat smaller, also are multiuser computers, intended to meet the needs of a small company by serving up to a hundred terminals. Microcomputers, computers powered by a microprocessor, are subdivided into personal computers and workstations, the latter typically incorporating RISC processors. Although microcomputers were originally single-user computers, the distinction between them and minicomputers has blurred as microprocessors have become more powerful. Linking multiple microcomputers together through a local area network or joining multiple microprocessors together in a parallel-processing system has enabled smaller systems to perform tasks once reserved for mainframes, and the techniques of grid computing have enabled computer scientists to utilize the unemployed processing power of computers connected over a network or the Internet.
Advances in the technology of integrated circuits have spurred the development of smaller and more powerful general-purpose digital computers. Not only has this reduced the size of the large, multi-user mainframe computers—which in their early years were large enough to walk through—to that of pieces of furniture, but it has also made possible powerful, single-user personal computers and workstations that can sit on a desktop or be easily carried. These, because of their relatively low cost and versatility, have replaced typewriters in the workplace and rendered the analog computer inefficient. The reduced size of computer components has also led to the development of thin, lightweight notebook computers and even smaller computer tablets and smartphones that have much more computing and storage capacity than that of the desktop computers that were available in the early 1990s.
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