A computer is a machine for manipulating data according to a list of instructions.
Computers take numerous physical forms. Early electronic computers were the size
of a large room, consuming as much power as several hundred modern personal computers.
[1] Today, computers can be made small enough to fit into a wrist watch and be powered
from a watch battery. Society has come to recognize personal computers and their
portable equivalent, the laptop computer, as icons of the information age; they
are what most people think of as "a computer". However, the most common form of
computer in use today is by far the embedded computer. Embedded computers are small,
simple devices that are often used to control other devices—for example, they may
be found in machines ranging from fighter aircraft to industrial robots, digital
cameras, and even children's toys.
A computer in a wristwatch. The ability to store and execute programs makes computers
extremely versatile and distinguishes them from calculators. The Church–Turing thesis
is a mathematical statement of this versatility: Any computer with a certain minimum
capability is, in principle, capable of performing the same tasks that any other
computer can perform. Therefore, computers with capability and complexity ranging
from that of a personal digital assistant to a supercomputer are all able to perform
the same computational tasks as long as time and storage capacity are not considerations.
History of computing
Main article: History of computing
The Jacquard loom was one of the first programmable devices. It is difficult to
define any one device as the earliest computer. The very definition of a computer
has changed and it is therefore impossible to identify the first computer. Many
devices once called "computers" would no longer qualify as such by today's standards.
Originally, the term "computer" referred to a person who performed numerical calculations
(a human computer), often with the aid of a mechanical calculating device. Examples
of early mechanical computing devices included the abacus, the slide rule and arguably
the astrolabe and the Antikythera mechanism (which dates from about 150-100 BC).
The end of the Middle Ages saw a re-invigoration of European mathematics and engineering,
and Wilhelm Schickard's 1623 device was the first of a number of mechanical calculators
constructed by European engineers.
However, none of those devices fit the modern definition of a computer because they
could not be programmed. In 1801, Joseph Marie Jacquard made an improvement to the
textile loom that used a series of punched paper cards as a template to allow his
loom to weave intricate patterns automatically. The resulting Jacquard loom was
an important step in the development of computers because the use of punched cards
to define woven patterns can be viewed as an early, albeit limited, form of programmability.
In 1837, Charles Babbage was the first to conceptualize and design a fully programmable
mechanical computer that he called "The Analytical Engine".[2] Due to limited finance,
and an inability to resist tinkering with the design, Babbage never actually built
his Analytical Engine.
Large-scale automated data processing of punched cards was performed for the US
Census in 1890 by tabulating machines designed by Herman Hollerith and manufactured
by the Computing Tabulating Recording Corporation, which later became IBM. By the
end of the 19th century a number of technologies that would later prove useful in
the realization of practical computers had begun to appear: the punched card, boolean
algebra, the vacuum tube (thermionic valve) and the teleprinter.
During the first half of the 20th century, many scientific computing needs were
met by increasingly sophisticated analog computers, which used a direct mechanical
or electrical model of the problem as a basis for computation. However, these were
not programmable and generally lacked the versatility and accuracy of modern digital
computers.
A succession of steadily more powerful and flexible computing devices were constructed
in the 1930s and 1940s, gradually adding the key features that are seen in modern
computers. The use of digital electronics (largely invented by Claude Shannon in
1937) and more flexible programmability were vitally important steps, but defining
one point along this road as "the first digital electronic computer" is difficult
(Shannon 1940). Notable achievements include:
EDSAC was one of the first computers to implement the stored program (von Neumann)
architecture. Konrad Zuse's electromechanical "Z machines". The Z3 (1941) was the
first working machine featuring binary arithmetic, including floating point arithmetic
and a measure of programmability. In 1998 the Z3 was proved to be Turing complete,
therefore being the world's first operational computer.
The Atanasoff-Berry Computer (1941) which used vacuum tube based computation, binary
numbers, and regenerative capacitor memory.
The secret British Colossus computer (1944), which had limited programmability but
demonstrated that a device using thousands of tubes could be reasonably reliable
and electronically reprogrammable. It was used for breaking German wartime codes.
The Harvard Mark I (1944), a large-scale electromechanical computer with limited
programmability.
The US Army's Ballistics Research Laboratory ENIAC (1946), which used decimal arithmetic
and was the first general purpose electronic computer, although it initially had
an inflexible architecture which essentially required rewiring to change its programming.
Several developers of ENIAC, recognizing its flaws, came up with a far more flexible
and elegant design, which came to be known as the stored program architecture or
von Neumann architecture. This design was first formally described by John von Neumann
in the paper "First Draft of a Report on the EDVAC", published in 1945. A number
of projects to develop computers based on the stored program architecture commenced
around this time, the first of these being completed in Great Britain. The first
to be demonstrated working was the Manchester Small-Scale Experimental Machine (SSEM)
or "Baby". However, the EDSAC, completed a year after SSEM, was perhaps the first
practical implementation of the stored program design. Shortly thereafter, the machine
originally described by von Neumann's paper—EDVAC—was completed but didn't see full-time
use for an additional two years.
Nearly all modern computers implement some form of the stored program architecture,
making it the single trait by which the word "computer" is now defined. By this
standard, many earlier devices would no longer be called computers by today's definition,
but are usually referred to as such in their historical context. While the technologies
used in computers have changed dramatically since the first electronic, general-purpose
computers of the 1940s, most still use the von Neumann architecture. The design
made the universal computer a practical reality.
Microprocessors are miniaturized devices that often implement stored program CPUs.
Vacuum tube-based computers were in use throughout the 1950s, but were largely replaced
in the 1960s by transistor-based devices, which were smaller, faster, cheaper, used
less power and were more reliable. These factors allowed computers to be produced
on an unprecedented commercial scale. By the 1970s, the adoption of integrated circuit
technology and the subsequent creation of microprocessors such as the Intel 4004
caused another leap in size, speed, cost and reliability. By the 1980s, computers
had become sufficiently small and cheap to replace simple mechanical controls
in domestic appliances such as washing machines. Around the same time, computers
became widely accessible for personal use by individuals in the form of home computers
and the now ubiquitous personal computer. In conjunction with the widespread growth
of the Internet since the 1990s, personal computers are becoming as common as the
television and the telephone and almost all modern electronic devices contain a
computer of some kind.
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