integrated circuit containing the arithmetic, logic, and control circuitry required to interpret and execute instructions from a computer program. When combined with other integrated circuits that provide storage for data and programs, often on a single semiconductor base to form a chip, the microprocessor becomes the heart of a small computer, or microcomputer. Microprocessors are classified by the semiconductor technology of their design (TTL, transistor-transistor logic; CMOS, complementary-metal-oxide semiconductor; or ECL, emitter-coupled logic), by the width of the data format (4-bit, 8-bit, 16-bit, 32-bit, or 64-bit) they process; and by their instruction set (CISC, complex-instruction-set computer, or RISC, reduced-instruction-set computer; see RISC processor). TTL technology is most commonly used, while CMOS is favored for portable computers and other battery-powered devices because of its low power consumption. ECL is used where the need for its greater speed offsets the fact that it consumes the most power. Four-bit devices, while inexpensive, are good only for simple control applications; in general, the wider the data format, the faster and more expensive the device. CISC processors, which have 70 to several hundred instructions, are easier to program than RISC processors, but are slower and more expensive.
Developed during the 1970s, the microprocessor became most visible as the central processor of the personal computer. Microprocessors also play supporting roles within larger computers as smart controllers for graphics displays, storage devices, and high-speed printers. However, the vast majority of microprocessors are used to control everything from consumer appliances to smart weapons. The microprocessor has made possible the inexpensive hand-held electronic calculator, the digital wristwatch, and the electronic game. Microprocessors are used to control consumer electronic devices, such as the programmable microwave oven and DVD player; to regulate gasoline consumption and antilock brakes in automobiles; to monitor alarm systems; and to operate automatic tracking and targeting systems in aircraft, tanks, and missiles and to control radar arrays that track and identify aircraft, among other defense applications.