In contrast, a digital computer uses symbolic representations of its variables. The arithmetic unit is constructed to follow the rules of one (or more) number systems. Further, the digital computer uses individual discrete states to represent the digits of the number system chosen. A digital computer can easily store and manipulate numbers, letters, images, sounds, or graphical information represented by a symbolic code. Through the use of the stored program, the digital computer achieves a degree of flexibility unequaled by any other computing or data-processing device.

The advent of the relatively inexpensive and readily available personal computer, and the combination of the computer and communications, such as by the use of networks, have dramatically expanded computer applications. The most common application now is probably text and word processing, followed by electronic mail. See also Electronic mail; Local-area networks; Microcomputer; Word processing.

Computers have begun to meet the barrier imposed by the speed of light in achieving higher speeds. This has led to research and development in the areas of parallel computers (in order to accomplish more in parallel rather than by serial computation) and distributed computers (taking advantage of network connections to spread the work around, thus achieving more parallelism). Continuing demand for more processing power has led to significant changes in computer hardware and software architectures, both to increase the speed of basic operations and to reduce the overall processing time. See also Computer systems architecture; Concurrent processing; Distributed systems (computers); Multiprocessing; Supercomputer.

An electronic device that stores and manipulates information. It differs from a calculator in being able to store a program and to store and retrieve information in its memory without human help. Business Dictionary:ComputerTopHome > Library > Business & Finance > Business Dictionary Machine capable of executing instructions to perform operations on data. The distinguishing feature of a computer is its ability to store its own instructions. This ability makes it possible for a computer to perform many operations without the need for a person to enter new instructions each time. Modern computers are made of high-speed electronic components that enable the computer to perform thousands of operations each second.

A device capable of accepting data in the form of facts and figures, manipulating them in a prescribed way, and supplying the results of these processes as meaningful information. This device usually consists of input and output devices, storage, arithmetic and logic units, and a control unit. Usually an automatic, stored-program machine is implied.

Any device capable of carrying out a sequence of operations in a defined manner. The definition of the operations is called the program. An analog computer performs computations by manipulating continuous physical variables, such as voltage and time. A digital computer operates on discrete quantities, most often represented as ‘on-off’, indicating whether the value of a binary variable is 0 or 1. Numbers and information are then represented by the binary system. Philosophically the excitement generated by computers has been in exploring the extent to which mental operations are well-represented as computations. See also artificial intelligence, Chinese room, connectionism, Turing machine, von Neumann machine.

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 by 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 connected computers.

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 large pieces of furniture, but it has also made possible powerful, single-user personal computers and workstations that can sit on a desktop. These, because of their relatively low cost and versatility, have largely replaced typewriters in the workplace and rendered the analog computer inefficient.

Analog Computers

An analog computer represents data as physical quantities and operates on the data by manipulating the quantities. It is designed to process data in which the variable quantities vary continuously (see analog circuit); it translates the relationships between the variables of a problem into analogous relationships between electrical quantities, such as current and voltage, and solves the original problem by solving the equivalent problem, or analog, that is set up in its electrical circuits. Because of this feature, analog computers were especially useful in the simulation and evaluation of dynamic situations, such as the flight of a space capsule or the changing weather patterns over a certain area. The key component of the analog computer is the operational amplifier, and the computer's capacity is determined by the number of amplifiers it contains (often over 100). Although analog computers are commonly found in such forms as speedometers and watt-hour meters, they largely have been made obsolete for general-purpose mathematical computations and data storage by digital computers.