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Microprocessors are silicon chips that contain a computer's central processing unit (CPU)the device that executes commands entered into the computer. Along with clocks and main memory, CPUs are among a computer's main components. The terms CPU and microprocessor often are used interchangeably. Essentially, microprocessors are responsible for manipulating data and performing numeric calculations and logical comparisons. At the heart of microprocessors are tiny electronic switches called transistors, which allow digital computers to process information in the form of electrical signals. These signals are in one of two states (on or off), and are represented by ones and zeroes, respectively. High-level programming languages like Java or C++, used to write popular software programs, eventually are translated to the machine language of ones and zeroes that computers understand.

Intel was the first company to produce a microprocessor for commercial use. Called the 4004, it was released in the early 1970s and contained slightly more than 2,000 transistors. By the early 2000s, microprocessors contained more than 5 million transistors on a single silicon chip. The more transistors a chip has, the more quickly it can process information. A microprocessor's clock speed defines the number of instructions it can carry out per second. This figure is expressed in Megahertz (MHz) or Gigahertz (GHz). In 2001 the processing speeds of some microprocessors exceeded 1.7 GHz.

In 1965, Intel Co-Founder Gordon E. Moore predicted the number of transistors manufacturers could fit onto a silicon chip would double every 18 months. Because his prediction proved to be accurate over time, it came to be known as Moore's Law. The law eventually will expire when it becomes physically impossible for manufacturers to fit any more transistors onto a single chip. This is expected to happen somewhere around 2017 or 2020 when transistors are atom-sized. At that time, a new computing architecture will be necessary. One possibility is quantum computing, which relies on atomic properties instead of transistors to determine the ones and zeros a computer understands. According to InfoWorld, "quantum computers rely on a particle's traits, such as the direction of its spin, for creating a state. For example, when the spin is up, a particle could be read as 'one,' and when its spin is down, the partide would be read as 'zero."'

In mid-2001 Intel announced experimental technology that it called "Wireless-Internet-On-A-Chip." Essentially, the technology consisted of a silicon chip that held a microprocessor, as well as analog communication circuits and flash memory. According to Intel, the technology potentially would lead to the development of more powerful wireless Internet devices. Around the same time, Intel and Hewlett-Packard announced the launch of the Itanium Processor, a new generation of microprocessor the companies co-developed for use in servers and workstation computers.


Borck, James R. "Life After Moore's Law: Quantum Computing." InfoWorld, October 16, 2000.

Intel Corp. "Intel Creates Technology To Enable 'Wireless-Internet-On-A-Chip."' Intel Corp., May 17, 2001. Available from www.intel.com/pressroom/archive.

. "Gordon E. Moore." Intel Corp., May 29, 2001. Available from www.intel.com/pressroom.

. "How Microprocessors Work." Intel Corp., May 29, 2001. Available from www.intel.com/education.

. "How Transistors Work." Intel Corp., May 29, 2001. Available from www.intel.com/education.

"Microprocessor." Ecommerce Webopedia, May 25, 2001. Available from www.e-comm.webopedia.com.

"Microprocessor." Tech Encyclopedia, May 25, 2001. Available from www.techweb.com.

SEE ALSO: Hardware; Intel Corp.; Moore, Gordon; Moore's Law; Programming Languages

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microprocessor A semiconductor chip, or chip set, that implements the central processor of a computer. Microprocessors consist of, at a minimum, an ALU and a control unit. They are characterized by speed, word length (internal and external), architecture, and instruction set, which may be either fixed or icroprogrammed. It is the combination of these characteristics and not just the cycle time that determines the performance of a microprocessor.

Most microprocessors have a fixed instruction set. Microprogrammed processors have a control store containing the microcode or firmware that defines the processor's instruction set; such processors may either be implemented on a single chip or constructed from bit-slice elements. RISC microprocessors are designed to execute a small number of simple instructions extremely fast.

The processor's architecture determines what register, stack, addressing, and I/O facilities are available, as well as defining the processor's primitive data types. The data types, which are the fundamental entities that can be manipulated by the instruction set, have included bit, nibble (4 bits), byte (8 bits), word (16 bits), and double words (32 bits). Note that a word is usually defined as the number of bits in the processor's internal data bus rather than always being 16 bits. Instructions generally include arithmetic, logical, flow-of-control, and data movement (between stacks, registers, memory, and I/O ports). With some microprocessors, coprocessors can be added to the system in order to extend the range of data types and instructions supported, e.g. floating-point numbers and the set of arithmetic operations defined on them.

The first microprocessor, the four-chip set Intel 4004, appeared in 1971 accompanied by considerable debate about its utility and marketability. It was the outcome of an idea proposed by Ted Hoff of Intel Corp. for a calculator that could implement a simple set of instructions in hardware but permitted complex sequences of them to be stored in a read-only memory (ROM). The result of his proposal was a design for a four-chip set consisting of a CPU, ROM, RAM, and a shift-register chip, the chip design proceeding in 1970 under the direction of Federico Faggin, later the founder of Zilog, Inc. The Intel 4004 had a 4-bit data bus, could address 4.5 Kbytes of memory, and had 45 instructions. Its 8-bit counterpart, the Intel 8008, was introduced in 1974 and its improved derivative, the Zilog Z80, in 1976. By this time there were over 50 microprocessors on the market.

The next generation of microprocessors included the Zilog Z8000, Motorola 68000, Intel 8086, National 16000, as well as the older Texas Instruments 9900 and Digital Equipment Corporation LSI-11. All of these chips use a 16-bit-wide external data bus. Higher performance microprocessors that use 32-bit external data buses include the Intel386, Intel486, Motorola 68030, and Digital's VAX 78032 and 78132 (processor and FPA). Processors using a 64-bit external bus are now available, an example being Intel's Pentium processor. RISC microprocessor chips with a 64-bit architecture include the PowerPC and Alpha AXP. Currently (2004) the market is dominated by Intel and AMD, with processors using clock frequencies of up to 3 GHz.

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microprocessor, 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.

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).

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mi·cro·proc·es·sor / ˌmīkrəˈpräsesər; -ˈprōˌsesər/ • n. an integrated circuit that contains all the functions of a central processing unit of a computer. DERIVATIVES: mi·cro·proc·ess·ing n.

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microprocessor Complex integrated circuit (chip) used to control the operation of a computer or other equipment.