A MICROPROCESSOR incorporates the functions of a computer's central processing unit (CPU) on a single integrated circuit (IC), or at most a few integrated circuits. All modern CPUs are microprocessors making the micro- prefix redundant. The microprocessor is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and provides results as output. It is an example of sequential digital logic, as it has internal memory. Microprocessors operate on numbers and symbols represented in the binary numeral system.
The advent of low-cost computers on integrated circuits has transformed modern society. General-purpose microprocessors in personal computers are used for computation, text editing, multimedia display, and communication over the Internet. Many more microprocessors are part of embedded systems, providing digital control over myriad objects from appliances to automobiles to cellular phones and industrial process control.
Intel introduced its first 4-bit microprocessor 4004 in 1971 and its 8-bit microprocessor 8008 in 1972. During the 1960s, computer processors were constructed out of small and medium-scale ICs—each containing from tens of transistors to a few hundred. These were placed and soldered onto printed circuit boards, and often multiple boards were interconnected in a chassis. The large number of discrete logic gates used more electrical power—and therefore produced more heat—than a more integrated design with fewer ICs. The distance that signals had to travel between ICs on the boards limited a computer's operating speed.
In the NASA Apollo space missions to the moon in the 1960s and 1970s, all onboard computations for primary guidance, navigation and control were provided by a small custom processor called "The Apollo Guidance Computer". It used wire wrap circuit boards whose only logic elements were three-input NOR gates.
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