Computer, automatic device capable of carrying out calculations according to a predetermined set of instructions. First developed in the 1940s, their technological development has been rapid. Computers have taken over routine commercial calculations and are used in scientific research and technology design. Computers are usually classified according to their mode of operation: analog, digital, or a combination of the 2. Analog computers use some measurable quantity to represent physically the calculation being carried out. They can perform simulations, such as the outcome of a missile launch or the effects of wind and rain on the flight of an aircraft. Digital computers (such as the personal computer) contain 4 basic units: an input/output device, an arithmetical unit to perform basic math operations, a memory, and a control unit to interpret instructions and supervise operations. The applications of digital computers include forecasting, management, and preparation. Computers in the 1990s are becoming faster, smaller, and more powerful. Engineers are working to make computers more sophisticated, user-friendly, and accessible to all aspects of life.