COMPUTER

any of various automatic electronic devices that solve problems by processing data according to a prescribed sequence of instructions. Such devices are of three general types: analog, digital, and hybrid. They differ from one another in terms of operating principle, equipment design, and application. The analog computer operates on data represented by continuously variable quantities, such as angular positions or voltages, and provides a physical analogy of the mathematical problem to be solved. Capable of solving ordinary differential equations, it is well suited for use in systems engineering, particularly for implementing real-time simulated models of processes and equipment. Another common application is the analysis of networks, such as those for electric-power distribution. Unlike the analog computer, which operates on continuous variables, the digital computer works with data in discrete formi.e., expressed directly as the digits of the binary code. It counts, lists, compares, and rearranges these binary digits, or bits, of data in accordance with very detailed program instructions stored within its memory. The results of these arithmetic and logic operations are translated into characters, numbers, and symbols that can be readily understood by the human operator or into signals intelligible to a machine controlled by the computer. Digital computers can be programmed to perform a host of varied tasks. As a consequence, more than 90 percent of the computers in use today are of this type. Government and business make extensive use of the digital computer's ability to organize, store, and retrieve information by setting up huge data files. Its capacity to adjust the performance of systems or devices without human intervention also lends itself to many applications. For example, the digital computer is used to control various manufacturing operations, machine tools, and complex laboratory and hospital instruments. The same capability has been exploited to automate the operational systems of high-performance aircraft and spacecraft. Among the multitude of other significant applications of the digital computer are its use as a teaching aid (e.g., in the remedial instruction of basic language and mathematics skills) and its employment in scientific research to analyze data and generate mathematical models. The hybrid computer combines the characteristics and advantages of analog and digital systems; it offers greater precision than the former and more control capability than the latter. Equipped with special conversion devices, it utilizes both analog and discrete representation of data. In recent years hybrid systems have been used in simulation studies of nuclear-power plants, guided-missile systems, and spacecraft, in which a close representation of a dynamic system is essential. Mechanical analog and digital computing devices date back to the 17th century. A logarithmic calculating device, which was the precursor of the slide rule and is often regarded as the first successful analog device, was developed in 1620 by Edmund Gunter, an English mathematician. The first mechanical digital calculating machine was built in 1642 by the French scientist-philosopher Blaise Pascal. During the ensuing centuries, the ideas and inventions of many mathematicians, scientists, and engineers paved the way for the development of the modern computer. The direct forerunners of present-day analog and digital systems emerged about 1940. John V. Atanasoff built the first electronic digital computer in 1939. Howard Aiken's fully automatic large-scale calculator using standard machine components was completed in 1944. J. Presper Eckert and John W. Mauchly completed the first programmed general-purpose electronic digital computer in 1946. The first stored-program computers were introduced in the late 1940s, and subsequent computers have increasingly become faster and more powerful.