microprocessor
micro
(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.
(2002-07-16)
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