microprocessor

architecture (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 databus (and instruction), its clock rate and its instructionset. 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 NS16000 and

NS32000, 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 IntelCorporation. Apple Computers, Inc. have also produced a

range of personal computers, as have several other companies.

See also killer micro, minicomputer, CPU Info Center.

(2002-07-16)