A microcomputer is a small, relatively inexpensive computer with a microprocessor as its central
processing unit.
It includes a microprocessor, memory, and input/output facilities.
Microcomputers became popular in the 1970s and 80s with the advent of increasingly powerful
microprocessors.
The predecessors to these computers, mainframes and minicomputers, were comparatively much
larger and more expensive.
Many microcomputers are also personal computers.
The abbreviation micro was common during the 1970s and 1980s, but has now fallen out of
common usage.
Origins The term microcomputer came into popular use
after the introduction of the minicomputer, although Isaac Asimov used the term microcomputer
in his short story "The Dying Night" as early as 1956.
Most notably, the microcomputer replaced the many separate components that made up the
minicomputer's CPU with one integrated microprocessor chip.
The French developers of the Micral N filed their patents with the term "Micro-ordinateur",
a literal equivalent of "Microcomputer", to designate the first solid state machine designed
with a microprocessor.
In the USA, the earliest models such as the Altair 8800 were often sold as kits to be
assembled by the user, and came with as little as 256 bytes of RAM, and no input/output devices
other than indicator lights and switches, useful as a proof of concept to demonstrate
what such a simple device could do.
However, as microprocessors and semiconductor memory became less expensive, microcomputers
in turn grew cheaper and easier to use: Increasingly inexpensive logic chips such
as the 7400 series allowed cheap dedicated circuitry for improved user interfaces such
as keyboard input, instead of simply a row of switches to toggle bits one at a time.
Use of audio cassettes for inexpensive data storage replaced manual re-entry of a program
every time the device was powered on.
Large cheap arrays of silicon logic gates in the form of Read-only memory and EPROMs
allowed utility programs and self-booting kernels to be stored within microcomputers.
These stored programs could automatically load further more complex software from external
storage devices without user intervention, to form an inexpensive turnkey system that
does not require a computer expert to understand or to use the device.
Random access memory became cheap enough to afford dedicating approximately 1-2 kilobytes
of memory to a video display controller frame buffer, for a 40x25 or 80x25 text display
or blocky color graphics on a common household television.
This replaced the slow, complex, and expensive teletypewriter that was previously common
as an interface to minicomputers and mainframes.
All these improvements in cost and usability resulted in an explosion in their popularity
during the late 1970s and early 1980s.
A large number of computer makers packaged microcomputers for use in small business applications.
By 1979, many companies such as Cromemco, Processor Technology, IMSAI, North Star Computers,
Southwest Technical Products Corporation, Ohio Scientific, Altos Computer Systems, Morrow
Designs and others produced systems designed either for a resourceful end user or consulting
firm to deliver business systems such as accounting, database management, and word processing to
small businesses.
This allowed businesses unable to afford leasing of a minicomputer or time-sharing service
the opportunity to automate business functions, without hiring a full-time staff to operate
the computers.
A representative system of this era would have used an S100 bus, an 8-bit processor
such as an Intel 8080 or Zilog Z80, and either CP/M or MP/M operating system.
The increasing availability and power of desktop computers for personal use attracted the attention
of more software developers.
In time, and as the industry matured, the market for personal computers standardized
around IBM PC compatibles running DOS, and later Windows.
Modern desktop computers, video game consoles, laptops, tablet PCs, and many types of handheld
devices, including mobile phones, pocket calculators, and industrial embedded systems, may all be
considered examples of microcomputers according to the definition given above.
Colloquial use of the term Everyday use of the expression "microcomputer"
has declined significantly from the mid-1980s and has declined in commonplace usage since
2000.
The term is most commonly associated with the first wave of all-in-one 8-bit home computers
and small business microcomputers.
Although, or perhaps because, an increasingly diverse range of modern microprocessor-based
devices fit the definition of "microcomputer," they are no longer referred to as such in
everyday speech.
In common usage, "microcomputer" has been largely supplanted by the term "personal computer"
or "PC," which specifies a computer that has been designed to be used by one individual
at a time, a term first coined in 1959.
IBM first promoted the term "personal computer" to differentiate themselves from other microcomputers,
often called "home computers", and also IBM's own mainframes and minicomputers . However,
following its release, the IBM PC itself was widely imitated, as well as the term.
The component parts were commonly available to producers and the BIOS was reverse engineered
through cleanroom design techniques.
IBM PC compatible "clones" became commonplace, and the terms "personal computer," and especially
"PC" stuck with the general public.
Since the advent of microcontrollers, the term "micro" is more commonly used to refer
to that meaning.
Description Monitors, keyboards and other devices for
input and output may be integrated or separate.
Computer memory in the form of RAM, and at least one other less volatile, memory storage
device are usually combined with the CPU on a system bus in one unit.
Other devices that make up a complete microcomputer system include batteries, a power supply unit,
a keyboard and various input/output devices used to convey information to and from a human
operator.
Microcomputers are designed to serve only one user at a time, although they can often
be modified with software or hardware to concurrently serve more than one user.
Microcomputers fit well on or under desks or tables, so that they are within easy access
of users.
Bigger computers like minicomputers, mainframes, and supercomputers take up large cabinets
or even dedicated rooms.
A microcomputer comes equipped with at least one type of data storage, usually RAM.
Although some microcomputers perform tasks using RAM alone, some form of secondary storage
is normally desirable.
In the early days of home micros, this was often a data cassette deck.
Later, secondary storage were built into the microcomputer case.
History
Although they did not contain any microprocessors, but were built around transistor-transistor
logic, Hewlett-Packard calculators as far back as 1968 had various levels of programmability
such that could be called microcomputers.
The HP 9100B had rudimentary conditional statements, statement line numbers, jump statements, registers
that could be used as variables, and primitive subroutines.
The programming language resembled Assembly language in many ways.
Later models incrementally added more features, including the BASIC programming language.
Some models had tape storage and small printers.
However, displays were limited to one line at a time.
[1] The HP 9100A was referred to as a personal computer in an advertisement in a 1968 Science
magazine, but that advertisement was quickly dropped.
It is suspected that HP was reluctant to call them "computers" because it would complicate
government procurement and export procedures.
The Datapoint 2200, made by CTC in 1970, is perhaps the best candidate for the title of
"first microcomputer".
While it contains no microprocessor, the instruction set of its custom TTL processor was the basis
of the instruction set for the Intel 8008, and for practical purposes the system behaves
approximately as if it contains an 8008.
This is because Intel was the contractor in charge of developing the Datapoint's CPU,
but ultimately CTC rejected the 8008 design because it needed 20 support chips.
Another early system, the Kenbak-1, was released in 1971.
Like the Datapoint 2200, it used discrete transistor–transistor logic instead of a
microprocessor, but it functioned like a microcomputer in most ways.
It was marketed as an educational and hobbyist tool, but it was not a commercial success;
production ceased shortly after introduction.
In 1972, a French team headed by François Gernelle within a small company, Réalisations
& Etudes Electroniqes, developed and patented a computer based on a microprocessor – the
Intel 8008 8-bit microprocessor.
This Micral-N was marketed in early 1973 as a "Micro-ordinateur" or microcomputer, mainly
for scientific and process-control applications.
About a hundred Micral-N were installed in the next two years, followed by a new version
based on the Intel 8080.
Meanwhile, another French team developed the Alvan, a small computer for office automation
which found clients in banks and other sectors.
The first version was based on LSI chips with an Intel 8008 as peripheral controller, before
adopting the Zilog Z80 as main processor.
In 1972, a Sacramento State University team led by Bill Pentz built the Sac State 8008
computer, able to handle thousands of patients' medical records.
The Sac State 8008 was designed with the Intel 8008.
It had a full set of hardware and software components: a disk operating system included
in a series of programmable read-only memory chips; 8 Kilobytes of RAM; IBM's Basic Assembly
Language; a hard drive; a color display; a printer output; a 150 bit/s serial interface
for connecting to a mainframe; and even the world's first microcomputer front panel.
Virtually all early microcomputers were essentially boxes with lights and switches; one had to
read and understand binary numbers and machine language to program and use them.
Of the early "box of switches"-type microcomputers, the MITS Altair 8800 was arguably the most
famous.
Most of these simple, early microcomputers were sold as electronic kits—bags full of
loose components which the buyer had to solder together before the system could be used.
The period from about 1971 to 1976 is sometimes called the first generation of microcomputers.
These machines were for engineering development and hobbyist personal use.
In 1975, the Processor Technology SOL-20 was designed, which consisted of one board which
included all the parts of the computer system.
The SOL-20 had built-in EPROM software which eliminated the need for rows of switches and
lights.
The MITS Altair just mentioned played an instrumental role in sparking significant hobbyist interest,
which itself eventually led to the founding and success of many well-known personal computer
hardware and software companies, such as Microsoft and Apple Computer.
Although the Altair itself was only a mild commercial success, it helped spark a huge
industry.
By 1977, the introduction of the second generation, known as home computers, made microcomputers
considerably easier to use than their predecessors because their predecessors' operation often
demanded thorough familiarity with practical electronics.
The ability to connect to a monitor or TV set allowed visual manipulation of text and
numbers.
The BASIC language, which was easier to learn and use than raw machine language, became
a standard feature.
These features were already common in minicomputers, with which many hobbyists and early produces
were familiar.
In 1979, the launch of the VisiCalc spreadsheet first turned the microcomputer from a hobby
for computer enthusiasts into a business tool.
After the 1981 release by IBM of its IBM PC, the term personal computer became generally
used for microcomputers compatible with the IBM PC architecture.
In 2012, the Raspberry Pi credit-card-sized single-board computer was launched, directly
inspired by Acorn's BBC Micro of 1981, and including support for BBC BASIC.
See also History of computing hardware
Lists of microcomputers Mainframe computer
Minicomputer Personal computer
Supercomputer References and footnotes