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integrated circuit containing the arithmetic, logic, and control circuitry required to interpret and execute instructions from a computer programcomputer program,
a series of instructions that a computer can interpret and execute; programs are also called software to distinguish them from hardware, the physical equipment used in data processing.
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. When combined with other integrated circuitsintegrated circuit
(IC), electronic circuit built on a semiconductor substrate, usually one of single-crystal silicon. The circuit, often called a chip, is packaged in a hermetically sealed case or a nonhermetic plastic capsule, with leads extending from it for input, output,
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 that provide storage for data and programs, often on a single semiconductorsemiconductor,
solid material whose electrical conductivity at room temperature is between that of a conductor and that of an insulator (see conduction; insulation). At high temperatures its conductivity approaches that of a metal, and at low temperatures it acts as an insulator.
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 base to form a chip, the microprocessor becomes the heart of a small computercomputer,
device capable of performing a series of arithmetic or logical operations. A computer is distinguished from a calculating machine, such as an electronic calculator, by being able to store a computer program (so that it can repeat its operations and make logical
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, 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 processorRISC processor
[Reduced Instruction Set Computer], computer arithmetic-logic unit that uses a minimal instruction set, emphasizing the instructions used most often and optimizing them for the fastest possible execution.
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). 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 computerpersonal computer
(PC), small but powerful computer primarily used in an office or home without the need to be connected to a larger computer. PCs evolved after the development of the microprocessor made possible the hobby-computer movement of the late 1970s, when some computers
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. 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 calculatorcalculator
or calculating machine,
device for performing numerical computations; it may be mechanical, electromechanical, or electronic. The electronic computer is also a calculator but performs other functions as well.
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, the digital wristwatch, and the electronic gameelectronic game,
device or computer program that provides entertainment by challenging a person's eye-hand coordination or mental abilities. Made possible by the development of the microprocessor, electronic games are marketed in various formats, such as hand-held one-player
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. 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.


See A. R. Ismail and V. M. Rooney, Microprocessor Hardware and Software Concepts (1987); I. L. Sayers, A. P. Robson, A. E. Adams, and G. E. Chester, Principles of Microprocessors (1991); M. Slater, A Guide to RISC Microprocessors (1992).


A single silicon chip on which the arithmetic and logic functions of a computer are placed.


Computing a single integrated circuit performing the basic functions of the central processing unit in a small computer


(Or "micro") A computer whose entire CPU is contained on one (or a small number of) integrated circuits.

The important characteristics of a microprocessor are the widths of its internal and external address bus and data bus (and instruction), its clock rate and its instruction set. Processors are also often classified as either RISC or CISC.

The first commercial microprocessor was the Intel 4004 which appeared in 1971. This was the CPU member of a set of four LSI integrated circuits called the MCS-4, which was originally designed for use in a calculator but was marketed as "programmable controller for logic replacement". The 4004 is referred to as a 4-bit microprocessor since it processed only 4 bits of data at a time. This very short word size is due mainly to the limitations imposed by the maximum integrated circuit density then achievable.

As integrated circuit densities increased with the rapid development of integrated circuit manufacturing technology, the power and performance of the microprocessors also increased. This is reflected in the increase in the CPU word size to 4, 8, 16, and by mid-1980s, 32 bits. The smaller microprocessors have relatively simple instruction sets, e.g., no floating point instructions, but they are nevertheless suitable as controllers for a very wide range of applications such as car engines and microwave ovens.

The Intel 4004 was followed with, among others the 4040, 8008, 8080, 8086, 80186, 80286, 80386, 486 and Pentium. Other families include the Motorola 6800 and 680x0 families, National Semiconductor 16000 and National Semiconductor 32000, SPARC, ARM, MIPS, Zilog Z8000, PowerPC and the Inmos Transputer family.

The larger, more recent microprocessors families have gradually acquired most of the features of large computers. As the microprocessor industry has matured, several families of microprocessors have evolved into de facto industrial standards with multiple manufacturers and numerous "support" chips including RAM, ROM, I/O controllers etc.

A single chip microprocessor may include other components such as memory (RAM, ROM, PROM), memory management, caches, floating-point unit, input/output ports and timers. Such devices are also known as microcontrollers.

The one-chip microcomputer is in many respects, a landmark development in computer technology because it reduces the computer to a small, inexpensive, and easily replaceable design component.

Microcomputers have given rise to a new class of general-purpose machines called personal computers. These are small low cost computers that are designed to sit on an ordinary office desk or to be portable and fuelled the computer boom of the late 1980s. The most widespread example is the also IBM PC, based on microprocessors from Intel Corporation. Apple Computers, Inc. have also produced a range of personal computers, as have several other companies.

See also killer micro, minicomputer, CPU Info Center.


A central processing unit (CPU) contained within a single chip (integrated circuit). The term originated in the 1970s when processors were first miniaturized. Today, all CPUs are microprocessors, and server, desktop, laptop, smartphone and tablet microprocessors have more than one processing unit (see dual core and multicore).

The term is often abbreviated MPU for "microprocessor unit" or just MP, the latter also spelled with the Greek µ symbol for micro or the letter "u" as an alternate (µP or uP).

From 8-Bit to 64-Bit
The earliest microprocessors were created by Texas Instruments, Intel and Scotland-based Pico Electronics, but who was really first has been debated. First-generation 8-bit microprocessor families were Intel's 8080, Zilog's Z80, Motorola's 6800 and Rockwell's 6502.

Today, the 32-bit and 64-bit microprocessors found in workstations and servers are x86, POWER and SPARC, while ARM leads the mobile market. The chips used in toys, appliances, vehicles and myriad other products are 8-, 16- and 32-bit microcontrollers, which include the microprocessor (see microcontroller). All together billions of microprocessors are made and shipped each year. See chip, embedded system, process technology, 16-bit computing, 32-bit computing and 64-bit computing.

The 386 Microprocessor
No technology is more incredible than the microprocessor. This older 386 chip contains a mere 275,000 transistors, and some slight detail can be seen. Contemporary chips at this magnification level show up only as a sea of gray. See chip. (Image courtesy of Intel Corporation.)

From 2K to Four Billion
This is a sampling of the number of transistors on a chip. It is not a comparison as many brands have similar transistor counts.
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