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| A computer is a machine that can be programmed to carry out sequences |
A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as programs. These programs enable computers to perform a wide range of tasks. A computer system is a nominally complete computer that includes the hardware, operating system (main software), and peripheral equipment needed and used for full operation. This term may also refer to a group of computers that are linked and function together, such as a computer network or computer cluster.
A
broad range of industrial and consumer products use computers as control systems.
Simple special-purpose devices like microwave ovens and remote controls are included,
as are factory devices like industrial robots and computer-aided design, as well
as general-purpose devices like personal computers and mobile devices like smartphones.
Computers power the Internet, which links billions of other computers and users.
Early
computers were meant to be used only for calculations. Simple manual instruments
like the ABACUS have aided people in doing calculations since ancient times.
Early in the Industrial Revolution, some mechanical devices were built to automate
long, tedious tasks, such as guiding patterns for looms. More sophisticated electrical
machines did specialize in ANALOG calculations in the early 20th century.
Computers
and computing devices from different eras.
Top row: automatic mechanical calculator (1820) (difference
engine), first-generation computer (Colossus
computer)
Middle row: early vacuum tube computer (ENIAC), supercomputer (IBM Summit)
Bottom row: video
game console (Nintendo GameCube), smartphone (LYF Water 2)
Main articles: History of Computing and
History of Computing hardware
For a chronological guide, see Timeline
of Computing.
PRE
20TH CENTURY
The Ishango bone, a bone tool dating back to prehistoric Africa
Devices
have been used to aid computation for thousands of years, mostly using one-to-one
correspondence with fingers. The earliest counting device was most likely a form
of tally stick. Later record-keeping aids throughout the Fertile Crescent included
calculi (clay spheres, cones, etc.) which represented counts of items, likely livestock
or grains, sealed in hollow unbaked clay containers. The use of counting rods is
one example.
The Chinese suanpan (算盘). The number represented on this abacus is 6,302,715,408.
The
abacus was initially used for arithmetic tasks. The Roman abacus was developed from
devices used in Babylonia as early as 2400 BC. Since then, many other forms of reckoning
boards or tables have been invented. In a medieval European counting house, a checkered
cloth would be placed on a table, and markers moved around on it according to certain
rules, as an aid to calculating sums of money.
The Antikythera mechanism, dating back to ancient Greece circa 150–100 BC, is an early analog computing device.
The
Antikythera mechanism is believed to be the earliest known mechanical analog computer,
according to Derek J. de Solla Price. It was designed to calculate astronomical
positions. It was discovered in 1901 in the Antikythera wreck off the Greek island
of Antikythera, between Kythera and Crete, and has been dated to approximately c. 100
BC. Devices of comparable complexity to the Antikythera mechanism would not reappear
until the fourteenth century.
Many
mechanical aids for calculation and measurement were constructed for astronomical
and navigation use. The planisphere was a star chart invented by Abū Rayhān al-Bīrūnī
in the early 11th century. The astrolabe was invented in the Hellenistic world in
either the 1st or 2nd centuries BC and is often attributed to Hipparchus. A combination
of the planisphere and dioptra, the astrolabe was effectively an analog computer
capable of working out several different kinds of problems in spherical astronomy.
The astrolabe incorporating the mechanical calendar computer and gear wheels was invented
by Abi Bakr of Isfahan, Persia in 1235. Abū Rayhān al-Bīrūnī invented the first
mechanical geared lunisolar calendar astrolabe, an early fixed-wired knowledge processing
machine with a gear train and gear wheels, c. 1000 AD.
The
sector, a calculating instrument used for solving problems in proportion, trigonometry,
multiplication, and division, and for various functions, such as squares and cube
roots, was developed in the late 16th century and found application in gunnery,
surveying, and navigation.
The
planimeter was a manual instrument to calculate the area of a closed figure by tracing
over it with a mechanical linkage.
A slide rule
The
slide rule was invented around 1620 - 1630 by the English clergyman William Oughtred,
shortly after the publication of the concept of the logarithm. It is a hand-operated
analog computer for doing multiplication and division. As slide rule development
progressed, added scales provided reciprocals, squares and square roots, cubes, and
cube roots, as well as transcendental functions such as logarithms and exponentials,
circular and hyperbolic trigonometry, and other functions. Slide rules with special
scales are still used for quick performance of routine calculations, such as the
E6B circular slide rule used for time and distance calculations on light aircraft.
In
the 1770s, Pierre Jaquet-Droz, a Swiss watchmaker, built a mechanical doll (automaton)
that could write holding a quill pen. By switching the number and order of its internal
wheels different letters, and hence different messages could be produced. In effect,
it could be mechanically "programmed" to read instructions. Along with
two other complex machines, the doll is at the Musée d'Art et d'Histoire of Neuchâtel,
Switzerland, and still operates.
In
1831-1835, mathematician and engineer Giovanni Plana devised a Perpetual Calendar
machine, which, through a system of pulleys and cylinders and over, could predict
the perpetual calendar for every year from AD 0 (that is, 1 BC) to AD 4000, keeping
track of leap years and varying day length. The tide-predicting machine invented
by the Scottish scientist Sir William Thomson in 1872 was of great utility to navigation
in shallow waters. It used a system of pulleys and wires to automatically calculate
predicted tide levels for a set period at a particular location.
The
differential analyzer, a mechanical analog computer designed to solve differential
equations by integration, used wheel-and-disc mechanisms to perform the integration.
In 1876, Sir William Thomson had already discussed the possible construction of
such calculators, but he had been stymied by the limited output torque of the ball-and-disk
integrators. In a differential analyzer, the output of one integrator drove the
input of the next integrator or a graphing output. The torque amplifier was the
advance that allowed these machines to work. Starting in the 1920s, Vannevar Bush
and others developed mechanical differential analyzers.
FIRST
COMPUTERS
A portion of Babbage's Difference engine
Charles
Babbage, an English mechanical engineer, and polymath originated the concept of
a programmable computer. Considered the "father of the computer", he conceptualized
and invented the first mechanical computer in the early 19th century.
After
working on his revolutionary difference engine, designed to aid in navigational
calculations, in 1833 he realized that a much more general design, an Analytical
Engine, was possible. The input of programs and data was to be provided to the machine
via punched cards, a method being used at the time to direct mechanical looms such
as the Jacquard loom. For output, the machine would have a printer, a curve plotter, and a bell. The machine would also be able to punch numbers onto cards to be read later. The Engine incorporated an arithmetic logic unit, control flow in the
form of conditional branching and loops, and integrated memory, making it the first
design for a general-purpose computer that could be described in modern terms as
Turing-complete.
The
machine was about a century ahead of its time. All the parts for his machine had
to be made by hand - this was a major problem for a device with thousands of parts.
Eventually, the project was dissolved with the decision of the British Government
to cease funding. Babbage's failure to complete the analytical engine can be chiefly
attributed to political and financial difficulties as well as his desire to develop
an increasingly sophisticated computer and to move ahead faster than anyone else
could follow. Nevertheless, his son, Henry Babbage, completed a simplified version
of the analytical engine's computing unit (the mill) in 1888. He gave a successful
demonstration of its use in computing tables in 1906.
ANALOGUE
COMPUTERS
Main article: Analog computer
Sir William Thomson's third tide-predicting machine design, 1879–81
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. The
first modern analog computer was the tide-predicting machine, invented by Sir William
Thomson (later to become Lord Kelvin) in 1872. The differential analyzer, a mechanical
analog computer designed to solve differential equations by integration using wheel-and-disc
mechanisms, was conceptualized in 1876 by James Thomson, the elder brother of the
more famous Sir William Thomson.
The
art of mechanical analog computing reached its zenith with the differential analyzer,
built by H. L. Hazen and Vannevar Bush at MIT starting in 1927. This was built on the
mechanical integrators of James Thomson and the torque amplifiers invented by H.
W. Nieman. A dozen of these devices were built before their obsolescence became
obvious. By the 1950s, the success of digital electronic computers had spelled the
end for most analog computing machines, but analog computers remained in use during
the 1950s in some specialized applications such as education (slide rule) and aircraft
(control systems).
DIGITAL
COMPUTERS
ELECTROMECHANICAL
By
1938, the United States Navy had developed an electromechanical analog computer
small enough to use aboard a submarine. This was the Torpedo Data Computer, which
used trigonometry to solve the problem of firing a torpedo at a moving target. During
World War II similar devices were developed in other countries as well.
Replica of Konrad Zuse's Z3, the first fully automatic, digital (electromechanical) computer
Early
digital computers were electromechanical; electric switches drove mechanical relays
to perform calculations. These devices had a low operating speed and were eventually
superseded by much faster all-electric computers, originally using vacuum tubes.
The Z2, created by German engineer Konrad Zuse in 1939 in Berlin, was one of the
earliest examples of an electromechanical relay computer.
Konrad Zuse, inventor of the modern computer
In
1941, Zuse followed his earlier machine up with the Z3, the world's first working
electromechanical programmable, fully automatic digital computer. The Z3 was built
with 2000 relays, implementing a 22-bit word length that operated at a clock frequency
of about 5–10 Hz. Program code was supplied on punched film while data could be
stored in 64 words of memory or supplied from the keyboard. It was quite similar
to modern machines in some respects, pioneering numerous advances such as floating-point
numbers. Rather than the harder-to-implement decimal system (used in Charles Babbage's
earlier design), using a binary system meant that Zuse's machines were easier to
build and potentially more reliable, given the technologies available at that time.
The Z3 was not itself a universal computer but could be extended to be Turing complete.
Zuse's
next computer, the Z4, became the world's first commercial computer; after an initial
delay due to the Second World War, it was completed in 1950 and delivered to the
ETH Zurich. The computer was manufactured by Zuse's own company, Zuse KG [de], which was founded in 1941 as the first
company with the sole purpose of developing computers.
VACUUM
TUBES AND DIGITAL ELECTRONICS CIRCUITS
Purely electronic circuit elements soon replaced their mechanical and electromechanical equivalents, at the same time that digital calculation replaced analog. The engineer Tommy Flowers, working at the Post Office Research Station in London in the 1930s, began to explore the possible use of electronics for the telephone exchange. Experimental equipment that he built in 1934 went into operation five years later, converting a portion of the telephone exchange network into an electronic data processing system, using thousands of vacuum tubes. In the US, John Vincent Atanasoff and Clifford E. Berry of Iowa State University developed and tested the Atanasoff–Berry Computer (ABC) in 1942, the first "automatic electronic digital computer". This design was also all-electronic and used about 300 vacuum tubes, with capacitors fixed in a mechanically rotating drum for memory.
Colossus, the first electronic digital programmable computing device, was used to break German ciphers during World War II. It is seen here in use at Bletchley Park in 1943.
During
World War II, the British code-breakers at Bletchley Park achieved a number of successes
at breaking encrypted German military communications. The German encryption machine,
Enigma, was first attacked with the help of the electro-mechanical bombes which
were often run by women. To crack the more sophisticated German Lorenz SZ 40/42
machine, used for high-level Army communications, Max Newman and his colleagues
commissioned Flowers to build the Colossus. He spent eleven months from early February
1943 designing and building the first Colossus. After a functional test in December
1943, Colossus was shipped to Bletchley Park, where it was delivered on 18 January
1944 and attacked its first message on 5 February.
Colossus
was the world's first electronic digital programmable computer. It used a large
number of valves (vacuum tubes). It had paper-tape input and was capable of being
configured to perform a variety of boolean logical operations on its data, but it
was not Turing-complete. Nine Mk II Colossi were built (The Mk I was converted to
an Mk II making ten machines in total). Colossus Mark, I contained 1,500 thermionic
valves (tubes), but Mark II with 2,400 valves, was five times faster and simpler
to operate than Mark I, greatly speeding the decoding process.
ENIAC was the first electronic, Turing-complete device, and performed ballistics trajectory calculations for the United States Army.
The
ENIAC (Electronic Numerical Integrator and Computer) was the first electronic programmable
computer built in the U.S. Although the ENIAC was similar to the Colossus, it was
much faster, more flexible, and it was Turing-complete. Like the Colossus, a "program"
on the ENIAC was defined by the states of its patch cables and switches, a far cry
from the stored program electronic machines that came later. Once a program was
written, it had to be mechanically set into the machine with manual resetting of
plugs and switches. The programmers of the ENIAC were six women, often known collectively
as the "ENIAC girls".
It
combined the high speed of electronics with the ability to be programmed for many
complex problems. It could add or subtract 5000 times a second, a thousand times
faster than any other machine. It also had modules to multiply, divide, and square
root. High-speed memory was limited to 20 words (about 80 bytes). Built under the
direction of John Mauchly and J. Presper Eckert at the University of Pennsylvania,
ENIAC's development and construction lasted from 1943 to full operation at the end
of 1945. The machine was huge, weighing 30 tons, using 200 kilowatts of electric
power, and contained over 18,000 vacuum tubes, 1,500 relays, and hundreds of thousands
of resistors, capacitors, and inductors.
THE FIRST DIGITAL electronic calculating machines were developed during World War II. The first semiconductor transistors in the late 1940s were followed by the silicon-based MOSFET (MOS transistor) and monolithic integrated circuit chip technologies in the late 1950s, leading to the microprocessor and the microcomputer revolution in the 1970s. The speed, power, and versatility of computers have been increasing dramatically ever since then, with transistor counts increasing at a rapid pace (as predicted by Moore's law), leading to the Digital Revolution during the late 20th to early 21st centuries.
Conventionally,
a modern computer consists of at least one processing element, typically a
central processing unit (CPU) in the form of a microprocessor, along with some
type of computer memory, typically semiconductor memory chips. The processing
element carries out arithmetic and logical operations, and a sequencing and
control unit can change the order of operations in response to stored
information. Peripheral devices include input devices (keyboards, mice,
joystick, etc.), output devices (monitor screens, printers, etc.), and
input/output devices that perform both functions (e.g., the 2000s-era
touchscreen). Peripheral devices allow information to be retrieved from an
external source and they enable the result of operations to be saved and
retrieved.
MODERN
COMPUTERS
CONCEPTS
OF MODERN COMPUTER
The
principle of the modern computer was proposed by Alan Turing in his seminal 1936
paper, On Computable Numbers. Turing proposed a simple device that he called a "Universal Computing machine" and that is now known as a universal Turing
machine. He proved that such a machine is capable of computing anything that is
computable by executing instructions (program) stored on tape, allowing the machine
to be programmable. The fundamental concept of Turing's design is the stored program,
where all the instructions for computing are stored in memory. Von Neumann acknowledged
that the central concept of the modern computer was due to this paper Turing machines
are to this day a central object of study in the theory of computation. Except for the
limitations imposed by their finite memory stores, modern computers are said to
be Turing-complete, which is to say, they have algorithm execution capability equivalent
to a universal Turing machine.
STORED
PROGRAMS
Main article: Stored-program computer
A section of the reconstructed Manchester Baby, the first electronic stored-program computer
Early
computing machines had fixed programs. Changing its function required the re-wiring
and re-structuring of the machine. With the proposal of the stored-program computer, this changed. A stored-program computer includes by design an instruction set and
can store in memory a set of instructions (a program) that details the computation.
The theoretical basis for the stored-program computer was laid out by Alan Turing
in his 1936 paper. In 1945, Turing joined the National Physical Laboratory and began
work on developing an electronic stored-program digital computer. His 1945 report
"Proposed Electronic Calculator" was the first specification for such
a device. John von Neumann at the University of Pennsylvania also circulated his
First Draft of a Report on EDVAC in 1945.
The
Manchester Baby was the world's first stored-program computer. It was built at the
University of Manchester in England by Frederic C. Williams, Tom Kilburn, and Geoff
Tootill, and ran its first program on 21 June 1948. It was designed as a testbed
for the Williams tube, the first random-access digital storage device. Although
the computer was described as "small and primitive" by a 1998 retrospective,
it was the first working machine to contain all of the elements essential to a modern
electronic computer. As soon as the Baby had demonstrated the feasibility of its
design, a project began at the university to develop it into a practically useful
computer, the Manchester Mark 1.
The
Mark 1 in turn quickly became the prototype for the Ferranti Mark 1, the world's
first commercially available general-purpose computer. Built by Ferranti, it was
delivered to the University of Manchester in February 1951. At least seven of these
later machines were delivered between 1953 and 1957, one of them to Shell labs in
Amsterdam. In October 1947 the directors of British catering company J. Lyons &
Company decided to take an active role in promoting the commercial development of
computers. Lyons's LEO I computer, modeled closely on the Cambridge EDSAC of 1949,
became operational in April 1951 and ran the world's first routine office computer
job.
Grace
Hopper was the first to develop a compiler for a programming language.
MOBILE
COMPUTERS
The
first mobile computers were heavy and ran from mains power. The 50 lb (23 kg) IBM
5100 was an early example. Later portables such as the Osborne 1 and Compaq Portable
were considerably lighter but still needed to be plugged in. The first laptops,
such as the Grid Compass, removed this requirement by incorporating batteries –
and with the continued miniaturization of computing resources and advancements in
portable battery life, portable computers grew in popularity in the 2000s. The same
developments allowed manufacturers to integrate computing resources into cellular
mobile phones by the early 2000s.
These
smartphones and tablets run on a variety of operating systems and recently became
the dominant computing device on the market. These are powered by Systems on a Chip
(SoCs), which are complete computers on a microchip the size of a coin.
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