computer: Digital Computers

A digital computer is designed to process data in numerical form (see digital circuit); its circuits perform directly the mathematical operations of addition, subtraction, multiplication, and division. The numbers operated on by a digital computer are expressed in the binary system; binary digits, or bits, are 0 and 1, so that 0, 1, 10, 11, 100, 101, etc., correspond to 0, 1, 2, 3, 4, 5, etc. Binary digits are easily expressed in the computer circuitry by the presence (1) or absence (0) of a current or voltage. A series of eight consecutive bits is called a “byte”; the eight-bit byte permits 256 different “on-off” combinations. Each byte can thus represent one of up to 256 alphanumeric characters, and such an arrangement is called a “single-byte character set” (SBCS); the de facto standard for this representation is the extended ASCII character set. Some languages, such as Japanese, Chinese, and Korean, require more than 256 unique symbols. The use of two bytes, or 16 bits, for each symbol, however, permits the representation of up to 65,536 characters or ideographs. Such an arrangement is called a “double-byte character set” (DBCS); Unicode is the international standard for such a character set. One or more bytes, depending on the computer's architecture, is sometimes called a digital word; it may specify not only the magnitude of the number in question, but also its sign (positive or negative), and may also contain redundant bits that allow automatic detection, and in some cases correction, of certain errors (see code; information theory). A digital computer can store the results of its calculations for later use, can compare results with other data, and on the basis of such comparisons can change the series of operations it performs. Digital computers are now used for a wide range of personal, business, scientific, and government purposes, from electronic games, e-mail, social networking, and data- and word-processing applications to desktop publishing, video conferencing, weather forecasting, simulated nuclear weapons testing, cryptography, and many other purposes.

Sections in this article:

• Introduction
• Development of Computers
• Computer Programs and Programming Languages
• Sharing the Computer's Resources
• Storage and Retrieval of Data
• Processing of Data
• Digital Computers
• Analog Computers
• Bibliography

The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2024, Columbia University Press. All rights reserved.

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