Computer.txt

Computer
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.

Computers and computing devices from different eras – clockwise from top left:
Early vacuum tube computer (ENIAC)
Mainframe computer (IBM System 360)
Desktop computer (IBM ThinkCentre S50 with monitor)
Supercomputer (IBM Summit)
Video game console (Nintendo GameCube)
Smartphone (LYF Water 2)

A broad range of industrial
and consumer products use
computers
as
control
systems. Simple specialpurpose 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 specialized analog calculations in the early 20th century. 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.

Etymology
According to the Oxford English Dictionary, the first known
use of computer was in a 1613 book called The Yong Mans
Gleanings by the English writer Richard Brathwait: "I haue
[sic] read the truest computer of Times, and the best
Arithmetician that euer [sic] breathed, and he reduceth thy
dayes into a short number." This usage of the term referred to a
human computer, a person who carried out calculations or
computations. The word continued with the same meaning
until the middle of the 20th century. During the latter part of
this period women were often hired as computers because they
could be paid less than their male counterparts.[1] By 1943,
most human computers were women.[2]

A human computer, with microscope and
calculator, 1952

The Online Etymology Dictionary gives the first attested use of
computer in the 1640s, meaning 'one who calculates'; this is an
"agent noun from compute (v.)". The Online Etymology Dictionary states that the use of the term to mean
" 'calculating machine' (of any type) is from 1897." The Online Etymology Dictionary indicates that the
"modern use" of the term, to mean 'programmable digital electronic computer' dates from "1945 under this
name; [in a] theoretical [sense] from 1937, as Turing machine".[3]

History
Pre-20th century
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.[a][4] The use of
counting rods is one example.
The abacus was initially used for arithmetic tasks. The Roman abacus was developed from devices used in
Babylonia as early as 2400 BCE. 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.[5]
The Antikythera mechanism is believed to be the earliest known mechanical analog computer, according to
Derek J. de Solla Price.[6] 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 BCE.
Devices of comparable complexity
to the Antikythera mechanism would
not reappear until the fourteenth
century.[7]
Many mechanical aids to calculation
and measurement were constructed
for astronomical and navigation use.
The Chinese suanpan (
). The number
The planisphere was a star chart
represented on this abacus is
invented by Abū Rayhān al-Bīrūnī
6,302,715,408.
in the early 11th century.[8] The
astrolabe was invented in the
Hellenistic world in either the 1st or 2nd centuries BCE 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. An astrolabe incorporating a mechanical
calendar computer[9][10] and gear-wheels was invented by Abi Bakr of
Isfahan, Persia in 1235.[11] Abū Rayhān al-Bīrūnī invented the first
mechanical geared lunisolar calendar astrolabe,[12] an early fixed-wired
knowledge processing machine[13] with a gear train and gear-wheels,[14]
c. 1000 AD.

算盘

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.

The Ishango bone, a
bone tool dating back
to prehistoric Africa

The Antikythera mechanism,
dating back to ancient Greece
circa 150–100 BCE, is an
early analog computing
device.

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 handoperated analog computer for doing multiplication and
A slide rule
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.[15]
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
0 CE (that is, 1 BCE) to 4000 CE, 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 analyser, 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.[16] 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 computer
Charles
Babbage,
an
English
mechanical engineer and polymath,
originated
the
concept
of
a
programmable computer. Considered
the "father of the computer",[17] he
conceptualized and invented the first
mechanical computer in the early 19th
century.
After working on his difference engine
he announced his invention in 1822, in
a paper to the Royal Astronomical
Society, titled "Note on the application
of machinery to the computation of
astronomical
and
mathematical
Charles Babbage c. 1850
[18]
tables",
he also 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 in 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 generalpurpose computer that could be described in modern terms as Turingcomplete.[19][20]

A diagram of a portion of
Babbage's Difference
engine

The Difference Engine
Number 2 at the Intellectual
Ventures laboratory in
Seattle

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.

In his work Essays on Automatics published in 1914, the Spanish engineer Leonardo Torres Quevedo
wrote a brief history of Babbage's efforts at constructing a mechanical Difference Engine and Analytical
Engine. He described the Analytical Engine as exemplifying his theories about the potential power of
machines, and takes the problem of designing such an engine as a challenge to his skills as an inventor of
electromechanical devices. The paper contains a design of a machine capable of calculating completely
automatically the value of the formula
, for a sequence of sets of values of the variables
involved. The whole machine was to be controlled by a read-only program, which was complete with
provisions for conditional branching. He also introduced the idea of floating-point arithmetic.[21][22] In
1920, to celebrate the 100th anniversary of the invention of the arithmometer, Torres presented in Paris the
Electromechanical Arithmometer, a prototype that used relays to implement the functions of an arithmetic
unit connected to a (possibly remote) typewriter, on which commands could be typed and the results printed
automatically.[23][24][25]

Analog computers

Sir William Thomson's third tidepredicting 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.[26] The first modern analog computer was a tide-predicting
machine, invented by Sir William Thomson (later to become Lord
Kelvin) in 1872. The differential analyser, 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.[16]

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 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.
Early digital computers were electromechanical; electric switches drove mechanical relays to perform the
calculation. These devices had a low operating speed and were eventually superseded by much faster allelectric 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.[27]

In 1941, Zuse followed his earlier machine up
with the Z3, the world's first working
electromechanical
programmable,
fully
[30][31]
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.[32] Program
code was supplied on punched film while
data could be stored in 64 words of memory
Replica of Konrad Zuse's Z3, the
or supplied from the keyboard. It was quite
first fully automatic, digital
Konrad Zuse,
similar to modern machines in some respects,
(electromechanical) computer
inventor of the
pioneering numerous advances such as
modern
floating-point numbers. Rather than the
computer[28][29]
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.[33] The Z3 was not itself a universal
computer but could be extended to be Turing complete.[34][35]
Zuse's next computer, the Z4, became the world's first commercial computer; after initial delay due to the
Second World War, it was completed in 1950 and delivered to the ETH Zurich.[36] The computer was
manufactured by Zuse's own company, Zuse KG, which was founded in 1941 as the first company with
the sole purpose of developing computers in Berlin.[36]
Vacuum tubes and digital electronic 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.[26] In the US, John Vincent Atanasoff and Clifford E. Berry of Iowa State
University developed and tested the Atanasoff–Berry Computer (ABC) in 1942,[37] the first "automatic
electronic digital computer".[38] This design was also all-electronic and used about 300 vacuum tubes, with
capacitors fixed in a mechanically rotating drum for memory.[39]
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.[40][41] 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.[39] He spent
eleven months from early February 1943 designing and
building the first Colossus.[42] After a functional test in
December 1943, Colossus was shipped to Bletchley Park,
where it was delivered on 18 January 1944[43] and attacked its
first message on 5 February.[39]

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.

Colossus was the world's first electronic digital programmable computer.[26] 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 a Mk II making ten machines in total). Colossus Mark I contained 1,500 thermionic
valves (tubes), but Mark II with 2,400 valves, was both five times faster and simpler to operate than Mark I,
greatly speeding the decoding process.[44][45]

ENIAC was the first electronic, Turingcomplete device, and performed ballistics
trajectory calculations for the United
States Army.

The ENIAC[46] (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 Turingcomplete. 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".[47][48]

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.[49]

Modern computers
Concept of modern computer
The principle of the modern computer was proposed by Alan Turing in his seminal 1936 paper,[50] On
Computable Numbers. Turing proposed a simple device that he called "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.[51] Turing machines are to this day a central object of study
in 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
Early computing machines had fixed programs. Changing its function required the re-wiring and restructuring of the machine.[39] With the proposal of the stored-program computer this changed. A storedprogram 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 the
EDVAC in 1945.[26]
The Manchester Baby was the world's first stored-program
computer. It was built at the University of Manchester in
A section of the reconstructed
England by Frederic C. Williams, Tom Kilburn and Geoff
Manchester Baby, the first electronic
Tootill, and ran its first program on 21 June 1948.[52] It was
stored-program computer
designed as a testbed for the Williams tube, the first randomaccess digital storage device.[53] 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.[54] 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.[55] 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.[56] 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, modelled closely on the Cambridge EDSAC of 1949, became operational in April
1951[57] and ran the world's first routine office computer job.
Grace Hopper was the first to develop a compiler for a programming language.[2]
Transistors
The concept of a field-effect transistor was proposed by Julius
Edgar Lilienfeld in 1925. John Bardeen and Walter Brattain, while
working under William Shockley at Bell Labs, built the first
working transistor, the point-contact transistor, in 1947, which was
followed by Shockley's bipolar junction transistor in 1948.[58][59]
From 1955 onwards, transistors replaced vacuum tubes in computer
designs, giving rise to the "second generation" of computers.
Compared to vacuum tubes, transistors have many advantages: they
are smaller, and require less power than vacuum tubes, so give off
Bipolar junction transistor (BJT)
less heat. Junction transistors were much more reliable than vacuum
tubes and had longer, indefinite, service life. Transistorized
computers could contain tens of thousands of binary logic circuits in a relatively compact space. However,
early junction transistors were relatively bulky devices that were difficult to manufacture on a massproduction basis, which limited them to a number of specialised applications.[60]
At the University of Manchester, a team under the leadership of Tom Kilburn designed and built a machine
using the newly developed transistors instead of valves.[61] Their first transistorised computer and the first
in the world, was operational by 1953, and a second version was completed there in April 1955. However,
the machine did make use of valves to generate its 125 kHz clock waveforms and in the circuitry to read

and write on its magnetic drum memory, so it was not the first completely transistorized computer. That
distinction goes to the Harwell CADET of 1955,[62] built by the electronics division of the Atomic Energy
Research Establishment at Harwell.[62][63]
The metal–oxide–silicon field-effect transistor (MOSFET), also
known as the MOS transistor, was invented by Mohamed M. Atalla
and Dawon Kahng at Bell Labs in 1959.[64] It was the first truly
compact transistor that could be miniaturised and mass-produced for
a wide range of uses.[60] With its high scalability,[65] and much
lower power consumption and higher density than bipolar junction
transistors,[66] the MOSFET made it possible to build high-density
integrated circuits.[67][68] In addition to data processing, it also
enabled the practical use of MOS transistors as memory cell storage
elements, leading to the development of MOS semiconductor
memory, which replaced earlier magnetic-core memory in
computers. The MOSFET led to the microcomputer revolution,[69]
and became the driving force behind the computer
revolution.[70][71] The MOSFET is the most widely used transistor
in computers,[72][73] and is the fundamental building block of
digital electronics.[74]

MOSFET (MOS transistor), showing
gate (G), body (B), source (S) and
drain (D) terminals. The gate is
separated from the body by an
insulating layer (pink).

Integrated circuits

Die photograph of a MOS 6502, Integrated circuits are typically packaged in
an early 1970s microprocessor plastic, metal, or ceramic cases to protect the IC
integrating 3500 transistors on a from damage and for ease of assembly.
single chip

The next great advance in computing power came with the advent of the integrated circuit (IC). The idea of
the integrated circuit was first conceived by a radar scientist working for the Royal Radar Establishment of
the Ministry of Defence, Geoffrey W.A. Dummer. Dummer presented the first public description of an
integrated circuit at the Symposium on Progress in Quality Electronic Components in Washington, D.C., on
7 May 1952.[75]
The first working ICs were invented by Jack Kilby at Texas Instruments and Robert Noyce at Fairchild
Semiconductor.[76] Kilby recorded his initial ideas concerning the integrated circuit in July 1958,
successfully demonstrating the first working integrated example on 12 September 1958.[77] In his patent
application of 6 February 1959, Kilby described his new device as "a body of semiconductor material ...

wherein all the components of the electronic circuit are completely integrated".[78][79] However, Kilby's
invention was a hybrid integrated circuit (hybrid IC), rather than a monolithic integrated circuit (IC)
chip.[80] Kilby's IC had external wire connections, which made it difficult to mass-produce.[81]
Noyce also came up with his own idea of an integrated circuit half a year later than Kilby.[82] Noyce's
invention was the first true monolithic IC chip.[83][81] His chip solved many practical problems that Kilby's
had not. Produced at Fairchild Semiconductor, it was made of silicon, whereas Kilby's chip was made of
germanium. Noyce's monolithic IC was fabricated using the planar process, developed by his colleague
Jean Hoerni in early 1959. In turn, the planar process was based on Mohamed M. Atalla's work on
semiconductor surface passivation by silicon dioxide in the late 1950s.[84][85][86]
Modern monolithic ICs are predominantly MOS (metal–oxide–semiconductor) integrated circuits, built
from MOSFETs (MOS transistors).[87] The earliest experimental MOS IC to be fabricated was a 16transistor chip built by Fred Heiman and Steven Hofstein at RCA in 1962.[88] General Microelectronics
later introduced the first commercial MOS IC in 1964,[89] developed by Robert Norman.[88] Following the
development of the self-aligned gate (silicon-gate) MOS transistor by Robert Kerwin, Donald Klein and
John Sarace at Bell Labs in 1967, the first silicon-gate MOS IC with self-aligned gates was developed by
Federico Faggin at Fairchild Semiconductor in 1968.[90] The MOSFET has since become the most critical
device component in modern ICs.[87]
The development of the MOS integrated circuit led to the invention of the microprocessor,[91][92] and
heralded an explosion in the commercial and personal use of computers. While the subject of exactly which
device was the first microprocessor is contentious, partly due to lack of agreement on the exact definition of
the term "microprocessor", it is largely undisputed that the first single-chip microprocessor was the Intel
4004,[93] designed and realized by Federico Faggin with his silicon-gate MOS IC technology,[91] along
with Ted Hoff, Masatoshi Shima and Stanley Mazor at Intel.[b][95] In the early 1970s, MOS IC technology
enabled the integration of more than 10,000 transistors on a single chip.[68]
System on a Chip (SoCs) are complete computers on a microchip (or chip) the size of a coin.[96] They may
or may not have integrated RAM and flash memory. If not integrated, the RAM is usually placed directly
above (known as Package on package) or below (on the opposite side of the circuit board) the SoC, and the
flash memory is usually placed right next to the SoC, this all done to improve data transfer speeds, as the
data signals do not have to travel long distances. Since ENIAC in 1945, computers have advanced
enormously, with modern SoCs (Such as the Snapdragon 865) being the size of a coin while also being
hundreds of thousands of times more powerful than ENIAC, integrating billions of transistors, and
consuming only a few watts of power.

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.[97] 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.[98] These are powered by System on a Chip (SoCs), which are complete
computers on a microchip the size of a coin.[96]

Types
Computers can be classified in a number of different ways, including:

By architecture
Analog computer
Digital computer
Hybrid computer
Harvard architecture
Von Neumann architecture
Complex instruction set computer
Reduced instruction set computer

By size, form-factor and purpose
Supercomputer
Mainframe computer
Minicomputer (term no longer used),[99] Midrange computer
Server
Rackmount server
Blade server
Tower server
Personal computer
Workstation
Microcomputer (term no longer used)[100]
Home computer (term fallen into disuse)[101]
Desktop computer
Tower desktop
Slimline desktop
Multimedia computer (non-linear editing system computers, video editing PCs
and the like, this term is no longer used)[102]
Gaming computer
All-in-one PC
Nettop (Small form factor PCs, Mini PCs)
Home theater PC
Keyboard computer
Portable computer
Thin client

Internet appliance
Laptop
Desktop replacement computer
Gaming laptop
Rugged laptop
2-in-1 PC
Ultrabook
Chromebook
Subnotebook
Netbook
Mobile computers:
Tablet computer
Smartphone
Ultra-mobile PC
Pocket PC
Palmtop PC
Handheld PC
Wearable computer
Smartwatch
Smartglasses
Single-board computer
Plug computer
Stick PC
Programmable logic controller
Computer-on-module
System on module
System in a package
System-on-chip (Also known as an Application Processor or AP if it lacks circuitry such as
radio circuitry)
Microcontroller

Hardware

Video demonstrating the standard
components of a "slimline" computer

The term hardware covers all of those parts of a computer that are tangible physical objects. Circuits,
computer chips, graphic cards, sound cards, memory (RAM), motherboard, displays, power supplies,
cables, keyboards, printers and "mice" input devices are all hardware.

History of computing hardware

First generation
(mechanical/electromechanical)

Second generation
(vacuum tubes)

Third generation
(discrete transistors and SSI, MSI,
LSI integrated circuits)

Fourth generation
(VLSI integrated circuits)

Calculators

Pascal's calculator, Arithmometer, Difference
engine, Quevedo's analytical machines

Programmable
devices

Jacquard loom, Analytical engine, IBM
ASCC/Harvard Mark I, Harvard Mark II, IBM
SSEC, Z1, Z2, Z3

Calculators

Atanasoff–Berry Computer, IBM 604, UNIVAC 60,
UNIVAC 120

Programmable
devices

Colossus, ENIAC, Manchester Baby, EDSAC,
Manchester Mark 1, Ferranti Pegasus, Ferranti
Mercury, CSIRAC, EDVAC, UNIVAC I, IBM 701,
IBM 702, IBM 650, Z22

Mainframes

IBM 7090, IBM 7080, IBM System/360, BUNCH

Minicomputer

HP 2116A, IBM System/32, IBM System/36,
LINC, PDP-8, PDP-11

Desktop Computer

HP 9100

Minicomputer

VAX, IBM AS/400

4-bit
microcomputer

Intel 4004, Intel 4040

8-bit
microcomputer

Intel 8008, Intel 8080, Motorola 6800, Motorola
6809, MOS Technology 6502, Zilog Z80

16-bit
microcomputer

Intel 8088, Zilog Z8000, WDC 65816/65802

32-bit
microcomputer

Intel 80386, Pentium, Motorola 68000, ARM

64-bit
microcomputer[c]

Alpha, MIPS, PA-RISC, PowerPC, SPARC, x8664, ARMv8-A

Embedded
computer

Intel 8048, Intel 8051

Personal computer

Desktop computer, Home computer, Laptop
computer, Personal digital assistant (PDA),
Portable computer, Tablet PC, Wearable computer

Quantum computer

IBM Q System One

Chemical computer
DNA computing
Theoretical/experimental

Optical computer
Spintronics-based
computer
Wetware/Organic
computer

Other hardware topics

Peripheral device
(input/output)

Computer buses

Input

Mouse, keyboard, joystick, image scanner, webcam,
graphics tablet, microphone

Output

Monitor, printer, loudspeaker

Both

Floppy disk drive, hard disk drive, optical disc drive,
teleprinter

Short range

RS-232, SCSI, PCI, USB

Long range (computer
networking)

Ethernet, ATM, FDDI

A general-purpose computer has four main components: the arithmetic logic unit (ALU), the control unit,
the memory, and the input and output devices (collectively termed I/O). These parts are interconnected by
buses, often made of groups of wires. Inside each of these parts are thousands to trillions of small electrical
circuits which can be turned off or on by means of an electronic switch. Each circuit represents a bit (binary
digit) of information so that when the circuit is on it represents a "1", and when off it represents a "0" (in
positive logic representation). The circuits are arranged in logic gates so that one or more of the circuits may
control the state of one or more of the other circuits.

Input devices
When unprocessed data is sent to the computer with the help of input devices, the data is processed and
sent to output devices. The input devices may be hand-operated or automated. The act of processing is
mainly regulated by the CPU. Some examples of input devices are:
Computer keyboard
Digital camera
Digital video
Graphics tablet
Image scanner
Joystick
Microphone
Mouse
Overlay keyboard
Real-time clock
Trackball
Touchscreen
Light pen

Output devices
The means through which computer gives output are known as output devices. Some examples of output
devices are:
Computer monitor
Printer
PC speaker

Projector
Sound card
Video card

Control unit
The control unit (often called a control system or
central controller) manages the computer's various
components; it reads and interprets (decodes) the
program instructions, transforming them into
control signals that activate other parts of the
computer.[d] Control systems in advanced
computers may change the order of execution of
some instructions to improve performance.

Diagram showing how a particular MIPS architecture
instruction would be decoded by the control system

A key component common to all CPUs is the
program counter, a special memory cell (a register) that keeps track of which location in memory the next
instruction is to be read from.[e]
The control system's function is as follows— this is a simplified description, and some of these steps may
be performed concurrently or in a different order depending on the type of CPU:
1. Read the code for the next instruction from the cell indicated by the program counter.
2. Decode the numerical code for the instruction into a set of commands or signals for each of
the other systems.
3. Increment the program counter so it points to the next instruction.
4. Read whatever data the instruction requires from cells in memory (or perhaps from an input
device). The location of this required data is typically stored within the instruction code.
5. Provide the necessary data to an ALU or register.
6. If the instruction requires an ALU or specialized hardware to complete, instruct the hardware
to perform the requested operation.
7. Write the result from the ALU back to a memory location or to a register or perhaps an output
device.
8. Jump back to step (1).
Since the program counter is (conceptually) just another set of memory cells, it can be changed by
calculations done in the ALU. Adding 100 to the program counter would cause the next instruction to be
read from a place 100 locations further down the program. Instructions that modify the program counter are
often known as "jumps" and allow for loops (instructions that are repeated by the computer) and often
conditional instruction execution (both examples of control flow).
The sequence of operations that the control unit goes through to process an instruction is in itself like a
short computer program, and indeed, in some more complex CPU designs, there is another yet smaller
computer called a microsequencer, which runs a microcode program that causes all of these events to
happen.

Central processing unit (CPU)

The control unit, ALU, and registers are collectively known as a central processing unit (CPU). Early
CPUs were composed of many separate components. Since the 1970s, CPUs have typically been
constructed on a single MOS integrated circuit chip called a microprocessor.

Arithmetic logic unit (ALU)
The ALU is capable of performing two classes of operations: arithmetic and logic.[103] The set of
arithmetic operations that a particular ALU supports may be limited to addition and subtraction, or might
include multiplication, division, trigonometry functions such as sine, cosine, etc., and square roots. Some
can operate only on whole numbers (integers) while others use floating point to represent real numbers,
albeit with limited precision. However, any computer that is capable of performing just the simplest
operations can be programmed to break down the more complex operations into simple steps that it can
perform. Therefore, any computer can be programmed to perform any arithmetic operation—although it
will take more time to do so if its ALU does not directly support the operation. An ALU may also compare
numbers and return Boolean truth values (true or false) depending on whether one is equal to, greater than
or less than the other ("is 64 greater than 65?"). Logic operations involve Boolean logic: AND, OR, XOR,
and NOT. These can be useful for creating complicated conditional statements and processing Boolean
logic.
Superscalar computers may contain multiple ALUs, allowing them to process several instructions
simultaneously.[104] Graphics processors and computers with SIMD and MIMD features often contain
ALUs that can perform arithmetic on vectors and matrices.

Memory
A computer's memory can be viewed as a list of cells into which
numbers can be placed or read. Each cell has a numbered "address"
and can store a single number. The computer can be instructed to
"put the number 123 into the cell numbered 1357" or to "add the
number that is in cell 1357 to the number that is in cell 2468 and put
the answer into cell 1595." The information stored in memory may
represent practically anything. Letters, numbers, even computer
instructions can be placed into memory with equal ease. Since the
CPU does not differentiate between different types of information,
it is the software's responsibility to give significance to what the
memory sees as nothing but a series of numbers.

Magnetic-core memory (using
magnetic cores) was the computer
memory of choice in the 1960s, until
it was replaced by semiconductor
memory (using MOS memory cells).

In almost all modern computers, each memory cell is set up to store
binary numbers in groups of eight bits (called a byte). Each byte is
able to represent 256 different numbers (28 = 256); either from 0 to
255 or −128 to +127. To store larger numbers, several consecutive bytes may be used (typically, two, four
or eight). When negative numbers are required, they are usually stored in two's complement notation. Other
arrangements are possible, but are usually not seen outside of specialized applications or historical contexts.
A computer can store any kind of information in memory if it can be represented numerically. Modern
computers have billions or even trillions of bytes of memory.
The CPU contains a special set of memory cells called registers that can be read and written to much more
rapidly than the main memory area. There are typically between two and one hundred registers depending
on the type of CPU. Registers are used for the most frequently needed data items to avoid having to access

main memory every time data is needed. As data is constantly being worked on, reducing the need to
access main memory (which is often slow compared to the ALU and control units) greatly increases the
computer's speed.
Computer main memory comes in two principal varieties:
random-access memory or RAM
read-only memory or ROM
RAM can be read and written to anytime the CPU commands it, but ROM is preloaded with data and
software that never changes, therefore the CPU can only read from it. ROM is typically used to store the
computer's initial start-up instructions. In general, the contents of RAM are erased when the power to the
computer is turned off, but ROM retains its data indefinitely. In a PC, the ROM contains a specialized
program called the BIOS that orchestrates loading the computer's operating system from the hard disk drive
into RAM whenever the computer is turned on or reset. In embedded computers, which frequently do not
have disk drives, all of the required software may be stored in ROM. Software stored in ROM is often
called firmware, because it is notionally more like hardware than software. Flash memory blurs the
distinction between ROM and RAM, as it retains its data when turned off but is also rewritable. It is
typically much slower than conventional ROM and RAM however, so its use is restricted to applications
where high speed is unnecessary.[f]
In more sophisticated computers there may be one or more RAM cache memories, which are slower than
registers but faster than main memory. Generally computers with this sort of cache are designed to move
frequently needed data into the cache automatically, often without the need for any intervention on the
programmer's part.

Input/output (I/O)
I/O is the means by which a computer exchanges information with
the outside world.[106] Devices that provide input or output to the
computer are called peripherals.[107] On a typical personal
computer, peripherals include input devices like the keyboard and
mouse, and output devices such as the display and printer. Hard
disk drives, floppy disk drives and optical disc drives serve as both
input and output devices. Computer networking is another form of
I/O. I/O devices are often complex computers in their own right,
Hard disk drives are common
with their own CPU and memory. A graphics processing unit might
storage devices used with
contain fifty or more tiny computers that perform the calculations
computers.
necessary to display 3D graphics. Modern desktop computers
contain many smaller computers that assist the main CPU in
performing I/O. A 2016-era flat screen display contains its own computer circuitry.

Multitasking
While a computer may be viewed as running one gigantic program stored in its main memory, in some
systems it is necessary to give the appearance of running several programs simultaneously. This is achieved
by multitasking i.e. having the computer switch rapidly between running each program in turn.[108] One
means by which this is done is with a special signal called an interrupt, which can periodically cause the
computer to stop executing instructions where it was and do something else instead. By remembering
where it was executing prior to the interrupt, the computer can return to that task later. If several programs

are running "at the same time". then the interrupt generator might be causing several hundred interrupts per
second, causing a program switch each time. Since modern computers typically execute instructions several
orders of magnitude faster than human perception, it may appear that many programs are running at the
same time even though only one is ever executing in any given instant. This method of multitasking is
sometimes termed "time-sharing" since each program is allocated a "slice" of time in turn.[109]
Before the era of inexpensive computers, the principal use for multitasking was to allow many people to
share the same computer. Seemingly, multitasking would cause a computer that is switching between
several programs to run more slowly, in direct proportion to the number of programs it is running, but most
programs spend much of their time waiting for slow input/output devices to complete their tasks. If a
program is waiting for the user to click on the mouse or press a key on the keyboard, then it will not take a
"time slice" until the event it is waiting for has occurred. This frees up time for other programs to execute so
that many programs may be run simultaneously without unacceptable speed loss.

Multiprocessing
Some computers are designed to distribute their work across
several CPUs in a multiprocessing configuration, a technique
once employed in only large and powerful machines such as
supercomputers, mainframe computers and servers.
Multiprocessor and multi-core (multiple CPUs on a single
integrated circuit) personal and laptop computers are now
widely available, and are being increasingly used in lower-end
markets as a result.
Supercomputers in particular often have highly unique
Cray designed many supercomputers that
architectures that differ significantly from the basic stored[g]
used multiprocessing heavily.
program architecture and from general-purpose computers.
They often feature thousands of CPUs, customized high-speed
interconnects, and specialized computing hardware. Such
designs tend to be useful for only specialized tasks due to the large scale of program organization required
to use most of the available resources at once. Supercomputers usually see usage in large-scale simulation,
graphics rendering, and cryptography applications, as well as with other so-called "embarrassingly parallel"
tasks.

Software
Software refers to parts of the computer which do not have a material form, such as programs, data,
protocols, etc. Software is that part of a computer system that consists of encoded information or computer
instructions, in contrast to the physical hardware from which the system is built. Computer software
includes computer programs, libraries and related non-executable data, such as online documentation or
digital media. It is often divided into system software and application software Computer hardware and
software require each other and neither can be realistically used on its own. When software is stored in
hardware that cannot easily be modified, such as with BIOS ROM in an IBM PC compatible computer, it is
sometimes called "firmware".

Operating system
/System Software

Library

Data

User interface

Application
Software

Unix and BSD

UNIX System V, IBM AIX, HP-UX, Solaris (SunOS), IRIX, List of
BSD operating systems

Linux

List of Linux distributions, Comparison of Linux distributions

Microsoft Windows

Windows 95, Windows 98, Windows NT, Windows 2000, Windows
ME, Windows XP, Windows Vista, Windows 7, Windows 8, Windows
8.1, Windows 10, Windows 11

DOS

86-DOS (QDOS), IBM PC DOS, MS-DOS, DR-DOS, FreeDOS

Macintosh
operating systems

Classic Mac OS, macOS (previously OS X and Mac OS X)

Embedded and
real-time

List of embedded operating systems

Experimental

Amoeba, Oberon–AOS, Bluebottle, A2, Plan 9 from Bell Labs

Multimedia

DirectX, OpenGL, OpenAL, Vulkan (API)

Programming
library

C standard library, Standard Template Library

Protocol

TCP/IP, Kermit, FTP, HTTP, SMTP

File format

HTML, XML, JPEG, MPEG, PNG

Graphical user
interface (WIMP)

Microsoft Windows, GNOME, KDE, QNX Photon, CDE, GEM, Aqua

Text-based user
interface

Command-line interface, Text user interface

Office suite

Word processing, Desktop publishing, Presentation program,
Database management system, Scheduling & Time management,
Spreadsheet, Accounting software

Internet Access

Browser, Email client, Web server, Mail transfer agent, Instant
messaging

Design and
manufacturing

Computer-aided design, Computer-aided manufacturing, Plant
management, Robotic manufacturing, Supply chain management

Graphics

Raster graphics editor, Vector graphics editor, 3D modeler, Animation
editor, 3D computer graphics, Video editing, Image processing

Audio

Digital audio editor, Audio playback, Mixing, Audio synthesis,
Computer music

Software
engineering

Compiler, Assembler, Interpreter, Debugger, Text editor, Integrated
development environment, Software performance analysis, Revision
control, Software configuration management

Educational

Edutainment, Educational game, Serious game, Flight simulator

Games

Strategy, Arcade, Puzzle, Simulation, First-person shooter, Platform,
Massively multiplayer, Interactive fiction

Misc

Artificial intelligence, Antivirus software, Malware scanner,
Installer/Package management systems, File manager

Languages
There are thousands of different programming languages—some intended for general purpose, others
useful for only highly specialized applications.

Programming languages
Lists of programming
languages

Timeline of programming languages, List of programming languages by category,
Generational list of programming languages, List of programming languages, NonEnglish-based programming languages

Commonly used assembly
languages

ARM, MIPS, x86

Commonly used high-level
programming languages

Ada, BASIC, C, C++, C#, COBOL, Fortran, PL/I, REXX, Java, Lisp, Pascal,
Object Pascal

Commonly used scripting
languages

Bourne script, JavaScript, Python, Ruby, PHP, Perl

Programs
The defining feature of modern computers which distinguishes them from all other machines is that they
can be programmed. That is to say that some type of instructions (the program) can be given to the
computer, and it will process them. Modern computers based on the von Neumann architecture often have
machine code in the form of an imperative programming language. In practical terms, a computer program
may be just a few instructions or extend to many millions of instructions, as do the programs for word
processors and web browsers for example. A typical modern computer can execute billions of instructions
per second (gigaflops) and rarely makes a mistake over many years of operation. Large computer programs
consisting of several million instructions may take teams of programmers years to write, and due to the
complexity of the task almost certainly contain errors.
Stored program architecture
This section applies to most common RAM machine–based
computers.
In most cases, computer instructions are simple: add one number to
another, move some data from one location to another, send a
message to some external device, etc. These instructions are read
from the computer's memory and are generally carried out
(executed) in the order they were given. However, there are usually
Replica of the Manchester Baby, the
specialized instructions to tell the computer to jump ahead or
world's first electronic storedbackwards to some other place in the program and to carry on
program computer, at the Museum of
executing from there. These are called "jump" instructions (or
Science and Industry in Manchester,
branches). Furthermore, jump instructions may be made to happen
England
conditionally so that different sequences of instructions may be used
depending on the result of some previous calculation or some
external event. Many computers directly support subroutines by providing a type of jump that "remembers"
the location it jumped from and another instruction to return to the instruction following that jump
instruction.
Program execution might be likened to reading a book. While a person will normally read each word and
line in sequence, they may at times jump back to an earlier place in the text or skip sections that are not of
interest. Similarly, a computer may sometimes go back and repeat the instructions in some section of the
program over and over again until some internal condition is met. This is called the flow of control within
the program and it is what allows the computer to perform tasks repeatedly without human intervention.

Comparatively, a person using a pocket calculator can perform a basic arithmetic operation such as adding
two numbers with just a few button presses. But to add together all of the numbers from 1 to 1,000 would
take thousands of button presses and a lot of time, with a near certainty of making a mistake. On the other
hand, a computer may be programmed to do this with just a few simple instructions. The following
example is written in the MIPS assembly language:
begin:
addi $8, $0, 0
addi $9, $0, 1
loop:
slti $10, $9, 1000
beq $10, $0, finish
add $8, $8, $9
addi $9, $9, 1
j loop
finish:
add $2, $8, $0

# initialize sum to 0
# set first number to add = 1
#
#
#
#
#

check if the number is less than 1000
if odd number is greater than n then exit
update sum
get next number
repeat the summing process

# put sum in output register

Once told to run this program, the computer will perform the repetitive addition task without further human
intervention. It will almost never make a mistake and a modern PC can complete the task in a fraction of a
second.
Machine code
In most computers, individual instructions are stored as machine code with each instruction being given a
unique number (its operation code or opcode for short). The command to add two numbers together would
have one opcode; the command to multiply them would have a different opcode, and so on. The simplest
computers are able to perform any of a handful of different instructions; the more complex computers have
several hundred to choose from, each with a unique numerical code. Since the computer's memory is able
to store numbers, it can also store the instruction codes. This leads to the important fact that entire programs
(which are just lists of these instructions) can be represented as lists of numbers and can themselves be
manipulated inside the computer in the same way as numeric data. The fundamental concept of storing
programs in the computer's memory alongside the data they operate on is the crux of the von Neumann, or
stored program, architecture.[111][112] In some cases, a computer might store some or all of its program in
memory that is kept separate from the data it operates on. This is called the Harvard architecture after the
Harvard Mark I computer. Modern von Neumann computers display some traits of the Harvard architecture
in their designs, such as in CPU caches.
While it is possible to write computer programs as long lists of numbers (machine language) and while this
technique was used with many early computers,[h] it is extremely tedious and potentially error-prone to do
so in practice, especially for complicated programs. Instead, each basic instruction can be given a short
name that is indicative of its function and easy to remember – a mnemonic such as ADD, SUB, MULT or
JUMP. These mnemonics are collectively known as a computer's assembly language. Converting programs
written in assembly language into something the computer can actually understand (machine language) is
usually done by a computer program called an assembler.
Programming language

Programming languages provide various ways of specifying
programs for computers to run. Unlike natural languages,
programming languages are designed to permit no ambiguity and to
be concise. They are purely written languages and are often difficult
to read aloud. They are generally either translated into machine
code by a compiler or an assembler before being run, or translated
directly at run time by an interpreter. Sometimes programs are
executed by a hybrid method of the two techniques.
Low-level languages

A 1970s punched card containing
one line from a Fortran program. The
card reads: "Z(1) = Y + W(1)" and is
labeled "PROJ039" for identification
purposes.

Machine languages and the assembly languages that represent them
(collectively termed low-level programming languages) are
generally unique to the particular architecture of a computer's central processing unit (CPU). For instance,
an ARM architecture CPU (such as may be found in a smartphone or a hand-held videogame) cannot
understand the machine language of an x86 CPU that might be in a PC.[i] Historically a significant number
of other cpu architectures were created and saw extensive use, notably including the MOS Technology
6502 and 6510 in addition to the Zilog Z80.
High-level languages
Although considerably easier than in machine language, writing long programs in assembly language is
often difficult and is also error prone. Therefore, most practical programs are written in more abstract highlevel programming languages that are able to express the needs of the programmer more conveniently (and
thereby help reduce programmer error). High level languages are usually "compiled" into machine
language (or sometimes into assembly language and then into machine language) using another computer
program called a compiler.[j] High level languages are less related to the workings of the target computer
than assembly language, and more related to the language and structure of the problem(s) to be solved by
the final program. It is therefore often possible to use different compilers to translate the same high level
language program into the machine language of many different types of computer. This is part of the means
by which software like video games may be made available for different computer architectures such as
personal computers and various video game consoles.
Program design
Program design of small programs is relatively simple and involves the analysis of the problem, collection
of inputs, using the programming constructs within languages, devising or using established procedures and
algorithms, providing data for output devices and solutions to the problem as applicable.[113] As problems
become larger and more complex, features such as subprograms, modules, formal documentation, and new
paradigms such as object-oriented programming are encountered.[114] Large programs involving thousands
of line of code and more require formal software methodologies.[115] The task of developing large software
systems presents a significant intellectual challenge.[116] Producing software with an acceptably high
reliability within a predictable schedule and budget has historically been difficult;[117] the academic and
professional discipline of software engineering concentrates specifically on this challenge.[118]
Bugs

Errors in computer programs are called "bugs". They may be
benign and not affect the usefulness of the program, or have only
subtle effects. However, in some cases they may cause the program
or the entire system to "hang", becoming unresponsive to input
such as mouse clicks or keystrokes, to completely fail, or to
crash.[119] Otherwise benign bugs may sometimes be harnessed for
malicious intent by an unscrupulous user writing an exploit, code
designed to take advantage of a bug and disrupt a computer's proper
execution. Bugs are usually not the fault of the computer. Since
computers merely execute the instructions they are given, bugs are
The actual first computer bug, a
nearly always the result of programmer error or an oversight made
moth found trapped on a relay of the
in the program's design.[k] Admiral Grace Hopper, an American
Harvard Mark II computer
computer scientist and developer of the first compiler, is credited for
having first used the term "bugs" in computing after a dead moth
was found shorting a relay in the Harvard Mark II computer in September 1947.[120]

Networking and the Internet
Computers have been used to coordinate information between
multiple locations since the 1950s. The U.S. military's SAGE
system was the first large-scale example of such a system, which
led to a number of special-purpose commercial systems such as
Sabre.[121] In the 1970s, computer engineers at research institutions
throughout the United States began to link their computers together
using telecommunications technology. The effort was funded by
ARPA (now DARPA), and the computer network that resulted was
called the ARPANET.[122] The technologies that made the Arpanet
possible spread and evolved.
In time, the network spread beyond academic and military
institutions and became known as the Internet. The emergence of
networking involved a redefinition of the nature and boundaries of
the computer. Computer operating systems and applications were
modified to include the ability to define and access the resources of
other computers on the network, such as peripheral devices, stored information, and the like, as extensions
of the resources of an individual computer. Initially these facilities were available primarily to people
working in high-tech environments, but in the 1990s the spread of applications like e-mail and the World
Wide Web, combined with the development of cheap, fast networking technologies like Ethernet and
ADSL saw computer networking become almost ubiquitous. In fact, the number of computers that are
networked is growing phenomenally. A very large proportion of personal computers regularly connect to
the Internet to communicate and receive information. "Wireless" networking, often utilizing mobile phone
networks, has meant networking is becoming increasingly ubiquitous even in mobile computing
environments.
Visualization of a portion of the
routes on the Internet

Unconventional computers
A computer does not need to be electronic, nor even have a processor, nor RAM, nor even a hard disk.
While popular usage of the word "computer" is synonymous with a personal electronic computer,[l] a
typical modern definition of a computer is: "A device that computes, especially a programmable [usually]

electronic machine that performs high-speed mathematical or logical operations or that assembles, stores,
correlates, or otherwise processes information."[123] According to this definition, any device that processes
information qualifies as a computer.

Future
There is active research to make computers out of many promising new types of technology, such as optical
computers, DNA computers, neural computers, and quantum computers. Most computers are universal, and
are able to calculate any computable function, and are limited only by their memory capacity and operating
speed. However different designs of computers can give very different performance for particular problems;
for example quantum computers can potentially break some modern encryption algorithms (by quantum
factoring) very quickly.

Computer architecture paradigms
There are many types of computer architectures:
Quantum computer vs. Chemical computer
Scalar processor vs. Vector processor
Non-Uniform Memory Access (NUMA) computers
Register machine vs. Stack machine
Harvard architecture vs. von Neumann architecture
Cellular architecture
Of all these abstract machines, a quantum computer holds the most promise for revolutionizing
computing.[124] Logic gates are a common abstraction which can apply to most of the above digital or
analog paradigms. The ability to store and execute lists of instructions called programs makes computers
extremely versatile, distinguishing them from calculators. The Church–Turing thesis is a mathematical
statement of this versatility: any computer with a minimum capability (being Turing-complete) is, in
principle, capable of performing the same tasks that any other computer can perform. Therefore, any type
of computer (netbook, supercomputer, cellular automaton, etc.) is able to perform the same computational
tasks, given enough time and storage capacity.

Artificial intelligence
A computer will solve problems in exactly the way it is programmed to, without regard to efficiency,
alternative solutions, possible shortcuts, or possible errors in the code. Computer programs that learn and
adapt are part of the emerging field of artificial intelligence and machine learning. Artificial intelligence
based products generally fall into two major categories: rule-based systems and pattern recognition systems.
Rule-based systems attempt to represent the rules used by human experts and tend to be expensive to
develop. Pattern-based systems use data about a problem to generate conclusions. Examples of patternbased systems include voice recognition, font recognition, translation and the emerging field of on-line
marketing.

Professions and organizations
As the use of computers has spread throughout society, there are an increasing number of careers involving
computers.

Computer-related professions
Hardwarerelated

Electrical engineering, Electronic engineering, Computer engineering, Telecommunications
engineering, Optical engineering, Nanoengineering

Softwarerelated

Computer science, Computer engineering, Desktop publishing, Human–computer interaction,
Information technology, Information systems, Computational science, Software engineering, Video
game industry, Web design

The need for computers to work well together and to be able to exchange information has spawned the
need for many standards organizations, clubs and societies of both a formal and informal nature.
Organizations
Standards groups

ANSI, IEC, IEEE, IETF, ISO, W3C

Professional societies

ACM, AIS, IET, IFIP, BCS

Free/open source software groups

Free Software Foundation, Mozilla Foundation, Apache Software Foundation

See also
Computability theory
Computer security
Glossary of computer hardware terms
History of computer science
List of computer term etymologies
List of computer system manufacturers

List of fictional computers
List of films about computers
List of pioneers in computer science
Pulse computation
TOP500 (list of most powerful computers)
Unconventional computing

Notes
a. According to Schmandt-Besserat 1981, these clay containers contained tokens, the total of
which were the count of objects being transferred. The containers thus served as something
of a bill of lading or an accounts book. In order to avoid breaking open the containers, first,
clay impressions of the tokens were placed on the outside of the containers, for the count;
the shapes of the impressions were abstracted into stylized marks; finally, the abstract marks
were systematically used as numerals; these numerals were finally formalized as numbers.
Eventually the marks on the outside of the containers were all that were needed to convey
the count, and the clay containers evolved into clay tablets with marks for the count.
Schmandt-Besserat 1999 estimates it took 4000 years.
b. The Intel 4004 (1971) die was 12 mm2, composed of 2300 transistors; by comparison, the
Pentium Pro was 306 mm2, composed of 5.5 million transistors.[94]
c. Most major 64-bit instruction set architectures are extensions of earlier designs. All of the
architectures listed in this table, except for Alpha, existed in 32-bit forms before their 64-bit
incarnations were introduced.
d. The control unit's role in interpreting instructions has varied somewhat in the past. Although
the control unit is solely responsible for instruction interpretation in most modern computers,
this is not always the case. Some computers have instructions that are partially interpreted
by the control unit with further interpretation performed by another device. For example,
EDVAC, one of the earliest stored-program computers, used a central control unit that
interpreted only four instructions. All of the arithmetic-related instructions were passed on to
its arithmetic unit and further decoded there.

e. Instructions often occupy more than one memory address, therefore the program counter
usually increases by the number of memory locations required to store one instruction.
f. Flash memory also may only be rewritten a limited number of times before wearing out,
making it less useful for heavy random access usage.[105]
g. However, it is also very common to construct supercomputers out of many pieces of cheap
commodity hardware; usually individual computers connected by networks. These so-called
computer clusters can often provide supercomputer performance at a much lower cost than
customized designs. While custom architectures are still used for most of the most powerful
supercomputers, there has been a proliferation of cluster computers in recent years.[110]
h. Even some later computers were commonly programmed directly in machine code. Some
minicomputers like the DEC PDP-8 could be programmed directly from a panel of switches.
However, this method was usually used only as part of the booting process. Most modern
computers boot entirely automatically by reading a boot program from some non-volatile
memory.
i. However, there is sometimes some form of machine language compatibility between
different computers. An x86-64 compatible microprocessor like the AMD Athlon 64 is able to
run most of the same programs that an Intel Core 2 microprocessor can, as well as programs
designed for earlier microprocessors like the Intel Pentiums and Intel 80486. This contrasts
with very early commercial computers, which were often one-of-a-kind and totally
incompatible with other computers.
j. High level languages are also often interpreted rather than compiled. Interpreted languages
are translated into machine code on the fly, while running, by another program called an
interpreter.
k. It is not universally true that bugs are solely due to programmer oversight. Computer
hardware may fail or may itself have a fundamental problem that produces unexpected
results in certain situations. For instance, the Pentium FDIV bug caused some Intel
microprocessors in the early 1990s to produce inaccurate results for certain floating point
division operations. This was caused by a flaw in the microprocessor design and resulted in
a partial recall of the affected devices.
l. According to the Shorter Oxford English Dictionary (6th ed, 2007), the word computer dates
back to the mid 17th century, when it referred to "A person who makes calculations;
specifically a person employed for this in an observatory etc."

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