Microprocessor - electronic circuit that functions as the central processing unit (CPU) of a computer, providing computational control. Microprocessors are also used in other advanced electronic systems, such as computer printers, automobiles, and jet airliners.

The most complicated ICs. They are composed of millions of transistors that have been configured as thousands of individual digital circuits, each of which performs some specific logic function. A microprocessor is built entirely of these logic circuits synchronized to each other. Just like marching band, the circuits perform their logic function only on direction by the bandmaster.

The BANDMASTER in a microprocessor, so to speak, is called the clock. The CLOCK is a signal that quickly alternates between two logic states. Every time the clock changes states, every logic circuit in the microprocessor does something. Calculations can be made very quickly, depending on the speed (“clock frequency”) of the microprocessor.

The microprocessor is one type of ultra-large-scale integrated circuit. Integrated circuits, also known as microchips or chips, are complex electronic circuits consisting of extremely tiny components formed on a single, thin, flat piece of material known as a semiconductor. Modern microprocessors incorporate transistors (which act as electronic amplifiers, oscillators, or, most commonly, switches), in addition to other

components such as resistors, diodes, capacitors, and wires, all packed into an area about the size of a postage stamp.HISTORY OF MICROPROCESSOR

The first microprocessor was the Intel 4004, produced in 1971. Originally developed for a calculator, and revolutionary for its time, it contained 2,300 transistors on a 4-bit microprocessor that could perform only 60,000 operations per second. The first 8-bit microprocessor was the Intel 8008, developed in 1972 to run computer terminals. The Intel 8008 contained 3,300 transistors. The first truly general-purpose microprocessor, developed in 1974, was the 8-bit Intel 8080 (see Microprocessor, 8080), which contained 4,500 transistors and could execute 200,000 instructions per second. By 1989, 32-bit microprocessors containing 1.2 million transistors and capable of executing 20 million instructions per second had been introduced.

In the 1990s the number of transistors on microprocessors continued to double nearly every 18 months. The rate of change followed an early prediction made by American semiconductor pioneer Gordon Moore. In 1965 Moore predicted that the number of transistors on a computer chip would double every year, a prediction that has come to be known as Moore’s Law. In the mid-1990s chips included the Intel Pentium Pro, containing 5.5 million transistors; the UltraSparc-II, by Sun Microsystems, containing 5.4 million transistors; the PowerPC620, developed jointly by Apple, IBM, and Motorola, containing 7 million transistors; and the Digital Equipment Corporation's Alpha 21164A, containing 9.3 million transistors. By the end of the decade microprocessors contained many millions of transistors, transferred 64 bits of data at once, and performed billions of instructions per second.

SEMICONDUCTOR

All integrated circuits are fabricated from semiconductors, substances whose ability to conduct electricity ranks between that of a conductor and that of a nonconductor, or insulator. Silicon is the most common semiconductor material. Because the electrical conductivity of a semiconductor can change according to the voltage applied to it, transistors made from semiconductors act like tiny switches that turn electrical current on and off in just a few nanoseconds (billionths of a second). This capability enables a computer to perform many billions of simple instructions each second and to complete complex tasks quickly.

The transistor used most commonly in the microelectronics industry is called a metal-oxide semiconductor field-effect transistor (MOSFET). It contains two n-type regions, called the source and the drain, with a p-type region in between them, called the channel. Over the channel is a thin layer of nonconductive silicon dioxide topped by another layer, called the gate. For electrons to flow from the source to the drain, a voltage (forward bias) must be applied to the gate. This causes the gate to act like a control switch, turning the MOSFET on and off and creating a logic gate that transmits digital 1s and 0s throughout the microprocessor.

Computer System

A typical computer system consists of a central processing unit (CPU), input devices, storage devices, and output devices. The CPU consists of an arithmetic/logic unit, registers, control section, and internal bus. The arithmetic/logic unit carries out

arithmetical and logical operations. The registers store data and keep track of operations. The control unit regulates and controls various operations. The internal bus connects the units of the CPU with each other and with external components of the system. For most computers, the principal input devices are a keyboard and a mouse. Storage devices include hard disks, CD-ROM drives, and random access memory (RAM) chips. Output devices that display data include monitors and printers.

Motherboard, in computer science, the main circuit board in a computer. The most important computer chips and other electronic components that give function to a computer are located on the motherboard. The motherboard is a printed circuit board that connects the various elements on it through the use of traces, or electrical pathways. The motherboard is indispensable to the computer and provides the main computing capability.

Personal computers normally have one central processing unit (CPU), or microprocessor, which is located with other chips on the motherboard. The manufacturer and model of the CPU chip carried by the motherboard is a key criterion for designating the speed and other capabilities of the computer. The CPU in many personal computers is not permanently attached to the motherboard, but is instead plugged into a socket so that it may be removed and upgraded.

Motherboards also contain important computing components, such as the basic input/output system (BIOS), which contains the basic set of instructions required to control the computer when it is first turned on; different types of memory chips such as random access memory (RAM) and cache memory; mouse, keyboard, and monitor control circuitry; and logic chips that control various parts of the computer’s function. Having as many of the key components of the computer as possible on the motherboard improves the speed and operation of the computer.

Users may expand their computer’s capability by inserting an expansion board into special expansion slots on the motherboard. Expansion slots are standard with nearly all personal computers and offer faster speed, better graphics capabilities, communication capability with other computers, and audio and video capabilities. Expansion slots come in either half or full size, and can transfer 8 or 16 bits (the smallest units of information that a computer can process) at a time, respectively.

The pathways that carry data on the motherboard are called buses. The amount of data that can be transmitted at one time between a device, such as a printer or monitor, and the CPU affects the speed at which programs run. For this reason, buses are designed to carry as much data as possible. To work properly, expansion boards must conform to bus standards such as integrated drive electronics (IDE), Extended Industry Standard Architecture (EISA), or small computer system interface (SCSI).