A computer is a
that can be programmed to carry out sequences of arithmetic or logical operations (
) 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
, operating system (main
), 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
and consumer products use computers as control systems. Simple special-purpose devices like microwave ovens and
remote control
remote control
s 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
s. Computers power the
Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, p ...

, which links billions of other computers and users. Early computers were meant to be used only for calculations. Simple manual instruments like the
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
s. 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
s in the late 1940s were followed by the
(MOS transistor) and monolithic integrated circuit chip technologies in the late 1950s, leading to the
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 A central processing unit (CPU), also called a central processor, main processor or just Processor (computing), processor, is the electronic circuitry that executes Instruction (computing), instructions comprising a computer program. The CPU per ...

central processing unit
(CPU) in the form of a microprocessor, along with some type of
computer memory In computing, memory is a device or system that is used to store information for immediate use in a computer or related computer hardware and Digital data, digital Electronics, electronic devices. The term ''memory'' is often synonymous with th ...
, typically
semiconductor memory Semiconductor memory is a digital electronics, digital electronic semiconductor device used for digital data storage, such as computer memory. It typically refers to devices in which data is stored within metal–oxide–semiconductor (MOS) memo ...
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 Information is an Abstraction, abstract concept that refers to that which has the power to Communication, inform. At the most fundamental level information pertains to the Interpretation (logic), interpretation of that which may be sensed. ...

. Peripheral devices include input devices (keyboards, mice,
joystick A joystick, sometimes called a flight stick, is an input device consisting of a stick that pivots on a base and reports its angle or direction to the device it is controlling. A joystick, also known as the control column, is the principal cont ...

, etc.), output devices (monitor screens, printers, etc.), and input/output devices that perform both functions (e.g., the 2000s-era
touchscreen A touchscreen or touch screen is the assembly of both an input ('touch panel') and output ('display') device. The touch panel is normally layered on the top of an electronic visual display of an information processing system. The display is ofte ...

). Peripheral devices allow information to be retrieved from an external source and they enable the result of operations to be saved and retrieved.


According to the ''
Oxford English Dictionary The ''Oxford English Dictionary'' (''OED'') is the first and foundational historical dictionary of the English language, published by Oxford University Press (OUP). It traces the historical development of the English language, providing a com ...
'', the first known use of ''computer'' was in a 1613 book called ''The Yong Mans Gleanings'' by the English writer Richard Brathwait: "I haue read the truest computer of Times, and the best Arithmetician that euer breathed, and he reduceth thy dayes into a short number." This usage of the term referred to a
human computer The term "computer", in use from the early 17th century (the first known written reference dates from 1613), meant "one who computes": a person performing mathematical calculations, before computer, electronic computers became commercially avai ...
, 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. By 1943, most human computers were women. The ''
Online Etymology Dictionary The ''Online Etymology Dictionary'' (''Etymonline'') is a free online dictionary, written and compiled by Douglas R. Harper, that describes the origins of English-language words. Description Douglas Harper, an American Civil War historian an ...
'' 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; n atheoretical
ense Ense () is a municipality in the Soest (district), district of Soest, in North Rhine-Westphalia, Germany. Geography Ense is situated on the river Möhne, approx. 12 km north-west of Arnsberg and 12 km south-west of Soest, Germany, Soest ...
from 1937, as ''
Turing machine A Turing machine is a mathematical model of computation describing an abstract machine that manipulates symbols on a strip of tape according to a table of rules. Despite the model's simplicity, it is capable of implementing any computer algori ...

Turing machine


Pre-20th century

Devices have been used to aid computation for thousands of years, mostly using
one-to-one correspondence In mathematics Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented in ...
. The earliest counting device was most likely a form of
tally stick A tally stick (or simply tally) was an ancient memory aid device used to record and document numbers, quantities and messages. Tally sticks first appear as animal bones carved with notches during the Upper Palaeolithic The Upper Paleolith ...
. Later record keeping aids throughout the
Fertile Crescent The Fertile Crescent ( ar, الهلال الخصيب) is a crescent-shaped region in the Middle East, spanning modern-day Iraq, Syria, Lebanon, Israel, State of Palestine, Palestine and Jordan, together with the northern region of Kuwait, sou ...

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 Counting rods () are small bars, typically 3–14 cm long, that were used by mathematicians for calculation in ancient East Asia. They are placed either horizontally or vertically to represent any integer or rational number. The written fo ...
is one example. The
was initially used for arithmetic tasks. The
Roman abacus The Ancient Romans developed the Roman hand abacus, a portable, but less capable, base-10 version of earlier abacuses like those that were used by the Greeks and Babylonians. Origin The Roman abacus was the first portable calculating device for E ...
was developed from devices used in
Babylonia Babylonia (; Akkadian: , ''māt Akkadī'') was an ancient Akkadian-speaking state and cultural area based in the city of Babylon in central-southern Mesopotamia (present-day Iraq and parts of Syria). It emerged as an Amorites, Amorite-ruled ...
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 counting house, or counting room, was traditionally an office in which the bookkeeping, financial books of a business were kept. It was also the place that the business received appointments and correspondence relating to demands for payment. A ...
, 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 The Antikythera mechanism ( ) is an Ancient Greece, Ancient Greek hand-powered orrery, described as the oldest example of an analogue computer used to predict astronomy, astronomical positions and eclipses decades in advance. It could also be ...

Antikythera mechanism
is believed to be the earliest known mechanical
analog computer An analog computer or analogue computer is a type of Computation, computer that uses the continuous variation aspect of physical phenomena such as Electrical network, electrical, Mechanics, mechanical, or Hydraulics, hydraulic quantities (''a ...
, according to Derek J. de Solla Price. It was designed to calculate astronomical positions. It was discovered in 1901 in the
Antikythera wreck The Antikythera wreck ( gr, Ναυάγιο των Αντικυθήρων) is a Roman-era shipwreck dating from the second quarter of the first century BC."''The Antikythera Shipwreck. The Ship, The Treasures, The Mechanism. National Archaeologic ...
off the Greek island of
Antikythera Antikythera or Anticythera ( ) is a Greek island lying on the edge of the Aegean Sea, between Crete and Peloponnese. In antiquity the island was known as (). Since the 2011 local government reform it is part of the municipality of Kythira islan ...

, between
Kythera Kythira (, ; el, Κύθηρα, , also transliterated as Cythera, Kythera and Kithira) is an Greek islands, island in Greece lying opposite the south-eastern tip of the Peloponnese peninsula. It is traditionally listed as one of the seven main Io ...
Crete Crete ( el, Κρήτη, translit=, Modern: , Ancient: ) is the largest and most populous of the Greek islands, the 88th largest island in the world and the fifth largest island in the Mediterranean Sea, after Sicily, Sardinia, Cyprus, ...

, and has been dated to approximately . Devices of comparable complexity to the Antikythera mechanism would not reappear until the fourteenth century. Many mechanical aids to calculation and measurement were constructed for astronomical and navigation use. The
planisphere In astronomy, a planisphere () is a star chart Analog computer, analog computing instrument in the form of two adjustable disks that rotate on a common pivot. It can be adjusted to display the visible stars for any time and date. It is an instru ...

was a
star chart A star chart is a celestial cartography, celestial map of the night sky with astronomical objects laid out on a grid system. They are used to identify and locate constellations, stars, nebulae, galaxy, galaxies, and planets. They have been used ...
invented by
Abū Rayhān al-Bīrūnī Abu Rayhan Muhammad ibn Ahmad al-Biruni (973 – after 1050) commonly known as al-Biruni, was a Khwarazmian Iranian peoples, Iranian in scholar and polymath during the Islamic Golden Age. He has been called variously the "founder of Indolog ...
in the early 11th century.G. Wiet, V. Elisseeff, P. Wolff, J. Naudu (1975). ''History of Mankind, Vol 3: The Great medieval Civilisations'', p. 649. George Allen & Unwin Ltd,
UNESCO The United Nations Educational, Scientific and Cultural Organization is a List of specialized agencies of the United Nations, specialized agency of the United Nations (UN) aimed at promoting world peace and security through international coope ...

astrolabe An astrolabe ( grc, ἀστρολάβος ; ar, ٱلأَسْطُرلاب ; persian, ستاره‌یاب ) is an ancient astronomical instrument that was a handheld model of the universe. Its various functions also make it an elaborate inclin ...

was invented in the
Hellenistic world In Classical antiquity, the Hellenistic period covers the time in History of the Mediterranean region, Mediterranean history after Classical Greece, between the death of Alexander the Great in 323 BC and the emergence of the Roman Empire, as sig ...
in either the 1st or 2nd centuries BC and is often attributed to
Hipparchus Hipparchus (; el, wikt:Ἵππαρχος, Ἵππαρχος, ''Hipparkhos'';  BC) was a Ancient astronomy, Greek astronomer, geographer, and mathematician. He is considered the founder of trigonometry, but is most famous for his incidenta ...
. A combination of the planisphere and
dioptra A dioptra (sometimes also named dioptre or diopter, from el, διόπτρα) is a Hellenistic civilization, classical astronomical and surveying instrument, dating from the 3rd century BC. The dioptra was a sighting tube or, alternatively ...

, 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 A calendar is a system of organizing days. This is done by giving names to periods of time, typically days, weeks, months and years. A date is the designation of a single and specific day within such a system. A calendar is also a ph ...

computer and
gear A gear is a rotating circular machine (mechanical), machine part having cut teeth or, in the case of a cogwheel or gearwheel, inserted teeth (called ''cogs''), which mesh with another (compatible) toothed part to transmit (convert) torque a ...

-wheels was invented by Abi Bakr of
Isfahan Isfahan ( fa, اصفهان, Esfahân ), from its Achaemenid empire, ancient designation ''Aspadana'' and, later, ''Spahan'' in Sassanian Empire, middle Persian, rendered in English as ''Ispahan'', is a major city in the Greater Isfahan Regio ...

Persia Iran, officially the Islamic Republic of Iran, and also called Persia, is a country located in Western Asia. It is bordered by Iraq and Turkey to the west, by Azerbaijan and Armenia to the northwest, by the Caspian Sea and Turkmeni ...

in 1235. Abū Rayhān al-Bīrūnī invented the first mechanical geared
lunisolar calendar A lunisolar calendar is a calendar in many cultures, combining lunar calendars and solar calendars. The date of Lunisolar calendars therefore indicates both the Moon phase and the time of the solar year, that is the position of the Sun in the Ea ...
astrolabe, an early fixed-
wire Overhead power cabling. The conductor consists of seven strands of steel (centre, high tensile strength), surrounded by four outer layers of aluminium (high conductivity). Sample diameter 40 mm A wire is a flexible strand of metal A me ...

d knowledge processing
with a
gear train A gear train is a mechanical system formed by mounting gears on a frame so the teeth of the gears engage. Gear teeth are designed to ensure the Pitch circle diameter (gears), pitch circles of engaging gears roll on each other without slipping, pr ...

gear train
and gear-wheels, . 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
was a manual instrument to calculate the area of a closed figure by tracing over it with a mechanical linkage. The
slide rule The slide rule is a mechanical analog computer which is used primarily for multiplication and division (mathematics), division, and for functions such as exponents, Nth root, roots, logarithms, and trigonometry. It is not typically designed for ...

slide rule
was invented around 1620–1630 by the English clergyman
William Oughtred William Oughtred ( ; 5 March 1574 – 30 June 1660), also Owtred, Uhtred, etc., was an Kingdom of England, English mathematician and Anglican ministry, Anglican clergyman.'Oughtred (William)', in P. Bayle, translated and revised by J.P. Bernar ...

William Oughtred
, shortly after the publication of the concept of the
logarithm In mathematics, the logarithm is the inverse function to exponentiation. That means the logarithm of a number  to the base  is the exponent to which must be raised, to produce . For example, since , the ''logarithm base'' 10 of ...

. 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 function In mathematics Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented in mod ...
s such as logarithms and exponentials, circular and
hyperbolic Hyperbolic is an adjective describing something that resembles or pertains to a hyperbola (a curve), to hyperbole (an overstatement or exaggeration), or to hyperbolic geometry. The following phenomena are described as ''hyperbolic'' because they ...

trigonometry Trigonometry () is a branch of mathematics that studies relationships between side lengths and angles of triangles. The field emerged in the Hellenistic period, Hellenistic world during the 3rd century BC from applications of geometry to Astr ...

and other functions. Slide rules with special scales are still used for quick performance of routine calculations, such as the
E6B The E6B flight computer is a form of circular slide rule used in aviation and one of the very few analog calculating devices in widespread use in the 21st century. They are mostly used in flight training, because these flight computers have bee ...
circular slide rule used for time and distance calculations on light aircraft. In the 1770s, Pierre Jaquet-Droz, a Swiss
watchmaker A watchmaker is an artisan who makes and repairs watches. Since a majority of watches are now factory-made, most modern watchmakers only repair watches. However, originally they were Master craftsman, master craftsmen who built watches, includ ...

, built a mechanical doll (
automaton An automaton (; plural: automata or automatons) is a relatively self-operating machine, or control mechanism designed to automatically follow a sequence of operations, or respond to predetermined instructions.Automaton – Definition and More ...
) 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 Neuchâtel (, , ; german: Neuenburg) is the capital of the Swiss canton of Canton of Neuchâtel, Neuchâtel, situated on the shoreline of Lake Neuchâtel. Since the fusion in 2021 of the municipalities of Neuchâtel, Corcelles-Cormondrèche, Peseu ...

Switzerland ). Swiss law does not designate a ''capital'' as such, but the federal parliament and government are in Bern, while other federal institutions, such as the federal courts, are in other cities (Bellinzona, Lausanne, Luzern, Neuchâtel, St. Gall ...

, and still operates. In 1831–1835, mathematician and engineer
Giovanni Plana
Giovanni Plana
devised a
Perpetual Calendar machine
Perpetual Calendar machine
, which, through a system of pulleys and cylinders and over, could predict the
perpetual calendar A perpetual calendar is a calendar A calendar is a system of organizing days. This is done by giving names to periods of time, typically days, weeks, months and years. A date is the designation of a single and specific day withi ...

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 analyser The differential analyser is a mechanical analogue computer designed to solve differential equation In mathematics, a differential equation is an functional equation, equation that relates one or more unknown function (mathematics), function ...
, a mechanical analog computer designed to solve
differential equation In mathematics, a differential equation is an functional equation, equation that relates one or more unknown function (mathematics), functions and their derivatives. In applications, the functions generally represent physical quantities, the der ...

differential equation
s by
, 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.Ray Girvan
"The revealed grace of the mechanism: computing after Babbage"
, ''Scientific Computing World'', May/June 2003
In a differential analyzer, the output of one integrator drove the input of the next integrator, or a graphing output. The
torque amplifier A torque amplifier is a mechanical device that amplifies the torque In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the cap ...
was the advance that allowed these machines to work. Starting in the 1920s,
Vannevar Bush Vannevar Bush ( ; March 11, 1890 – June 28, 1974) was an American engineer, inventor and science administrator, who during World War II, World War II headed the U.S. Office of Scientific Research and Development (OSRD), through which almo ...

Vannevar Bush
and others developed mechanical differential analyzers.

First computer

Charles Babbage Charles Babbage (; 26 December 1791 – 18 October 1871) was an English polymath. A mathematician, philosopher, inventor and mechanical engineer, Babbage originated the concept of a digital programmable computer. Babbage is considered ...

Charles Babbage
, an English mechanical engineer and
polymath A polymath ( el, πολυμαθής, , "having learned much"; la, homo universalis, "universal human") is an individual whose knowledge spans a substantial number of subjects, known to draw on complex bodies of knowledge to solve specific pro ...

, originated the concept of a programmable computer. Considered the " father of the computer", he conceptualized and invented the first
mechanical computer A mechanical computer is a computer built from machine, mechanical components such as levers and gears rather than electronics, electronic components. The most common examples are adding machines and mechanical counters, which use the turning of g ...
in the early 19th century. After working on his revolutionary
difference engine A difference engine is an automatic mechanical calculator designed to tabulate polynomial, polynomial functions. It was designed in the 1820s, and was first created by Charles Babbage. The name, the difference engine, is derived from the method ...

difference engine
, designed to aid in navigational calculations, in 1833 he realized that a much more general design, an
Analytical Engine The Analytical Engine was a proposed mechanical general-purpose computer designed by English mathematician and computer pioneer Charles Babbage. It was first described in 1837 as the successor to Babbage's difference engine, which was a des ...
, was possible. The input of programs and data was to be provided to the machine via
punched card A punched card (also punch card or punched-card) is a piece of stiff paper that holds digital data represented by the presence or absence of holes in predefined positions. Punched cards were once common in data processing applications or to di ...

punched card
s, a method being used at the time to direct mechanical
s such as the
Jacquard loom The Jacquard machine () is a device fitted to a loom that simplifies the process of manufacturing textiles with such complex patterns as brocade, damask and matelassé. The resulting ensemble of the loom and Jacquard machine is then called a Jac ...

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 In computing, an arithmetic logic unit (ALU) is a Combinational logic, combinational digital circuit that performs arithmetic and bitwise operations on integer binary numbers. This is in contrast to a floating-point unit (FPU), which operates on ...
, control flow in the form of conditional branching and program loop#Loops, loops, and integrated computer memory, 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.

Analog computers

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
. However, these were not programmable and generally lacked the versatility and accuracy of modern digital computers. 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 The differential analyser is a mechanical analogue computer designed to solve differential equation In mathematics, a differential equation is an functional equation, equation that relates one or more unknown function (mathematics), function ...
, a mechanical analog computer designed to solve differential equations by integration using wheel-and-disc mechanisms, was conceptualized in 1876 by James Thomson (engineer), 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 Vannevar Bush ( ; March 11, 1890 – June 28, 1974) was an American engineer, inventor and science administrator, who during World War II, World War II headed the U.S. Office of Scientific Research and Development (OSRD), through which almo ...

Vannevar Bush
at Massachusetts Institute of Technology, MIT starting in 1927. This built on the mechanical integrators of James Thomson (engineer), 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 The slide rule is a mechanical analog computer which is used primarily for multiplication and division (mathematics), division, and for functions such as exponents, Nth root, roots, logarithms, and trigonometry. It is not typically designed for ...

slide rule
) and aircraft ( control systems).

Digital computers


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 electromechanics, electromechanical; electric switches drove mechanical relays to perform the calculation. These devices had a low operating speed and were eventually superseded by much faster all-electric computers, originally using vacuum tubes. The Z2 (computer), Z2, created by German engineer Konrad Zuse in 1939, was one of the earliest examples of an electromechanical relay computer. In 1941, Zuse followed his earlier machine up with the Z3 (computer), Z3, the world's first working electromechanical Computer programming, programmable, fully automatic digital computer. The Z3 was built with 2000 relays, implementing a 22 bit Word (computer architecture), word length that operated at a clock frequency of about 5–10 Hertz, Hz. Program code was supplied on punched celluloid, 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 Charles Babbage (; 26 December 1791 – 18 October 1871) was an English polymath. A mathematician, philosopher, inventor and mechanical engineer, Babbage originated the concept of a digital programmable computer. Babbage is considered ...

Charles Babbage
's earlier design), using a binary number, 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 (computer), 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. The computer was manufactured by Zuse's own company, , which was founded in 1941 as the first company with the sole purpose of developing computers.

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. In the US, John Vincent Atanasoff and Clifford Berry, 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. 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 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 computer, 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 electronics, electronic Digital electronics, digital Computer programming, 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 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. 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.

Modern computers

Concept 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 "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. John von Neumann, 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 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 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 computer program, program) that details the . 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 (United Kingdom), 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. The Manchester Baby was the world's first stored-program computer. It was built at the University of Manchester in England by Frederic Calland Williams, 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 memory, 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 Royal Dutch Shell, Shell labs in Amsterdam. In October 1947 the directors of British catering company J. Lyons and Co., J. Lyons & Company decided to take an active role in promoting the commercial development of computers. Lyons's LEO computer, LEO I computer, modelled closely on the University of Cambridge, Cambridge Electronic Delay Storage Automatic Calculator, EDSAC of 1949, became operational in April 1951 and ran the world's first routine office computer job (software), job. Grace Hopper was the first to develop a compiler for a programming language.


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 , the point-contact transistor, in 1947, which was followed by Shockley's bipolar junction transistor in 1948. 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 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 mass-production basis, which limited them to a number of specialised applications. 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. Their first transistor computer, transistorised computer and the first in the world, was Manchester computers#Transistor Computer, 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, built by the electronics division of the Atomic Energy Research Establishment at Harwell, Oxfordshire, Harwell. The MOSFET, 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. It was the first truly compact transistor that could be miniaturised and mass-produced for a wide range of uses. With its MOSFET scaling, high scalability, and much lower power consumption and higher density than bipolar junction transistors, the MOSFET made it possible to build Very large-scale integration, high-density integrated circuits. In addition to data processing, it also enabled the practical use of MOS transistors as memory cell (computing), memory cell storage elements, leading to the development of MOS
semiconductor memory Semiconductor memory is a digital electronics, digital electronic semiconductor device used for digital data storage, such as computer memory. It typically refers to devices in which data is stored within metal–oxide–semiconductor (MOS) memo ...
, which replaced earlier magnetic-core memory in computers. The MOSFET led to the microcomputer revolution, and became the driving force behind the computer revolution. The MOSFET is the most widely used transistor in computers, and is the fundamental building block of digital electronics.

Integrated circuits

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 (United Kingdom), Ministry of Defence, Geoffrey Dummer, 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., Washington, D.C. on 7 May 1952. The first working ICs were invented by Jack Kilby at Texas Instruments and Robert Noyce at Fairchild Semiconductor. Kilby recorded his initial ideas concerning the integrated circuit in July 1958, successfully demonstrating the first working integrated example on 12 September 1958.''The Chip that Jack Built''
, (c. 2008), (HTML), Texas Instruments, Retrieved 29 May 2008.
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". However, Kilby's invention was a hybrid integrated circuit (hybrid IC), rather than a monolithic integrated circuit (IC) chip. Kilby's IC had external wire connections, which made it difficult to mass-produce. Noyce also came up with his own idea of an integrated circuit half a year later than Kilby. Noyce's invention was the first true monolithic IC chip. His chip solved many practical problems that Kilby's had not. Produced at Fairchild Semiconductor, it was made of , whereas Kilby's chip was made of germanium. Noyce's monolithic IC was semiconductor device fabrication, 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. Modern monolithic ICs are predominantly MOS (metal-oxide-semiconductor) integrated circuits, built from s (MOS transistors). The earliest experimental MOS IC to be fabricated was a 16-transistor chip built by Fred Heiman and Steven Hofstein at RCA in 1962. General Microelectronics later introduced the first commercial MOS IC in 1964, developed by Robert Norman. Following the development of the self-aligned gate (silicon-gate) MOS transistor by Robert Kerwin, Donald L. Klein, 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. The MOSFET has since become the most critical device component in modern ICs. The development of the MOS integrated circuit led to the invention of the , 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, designed and realized by Federico Faggin with his silicon-gate MOS IC technology, along with Marcian Hoff, Ted Hoff, Masatoshi Shima and Stanley Mazor at Intel.Federico Faggin
The Making of the First Microprocessor
, ''IEEE Solid-State Circuits Magazine'', Winter 2009, IEEE Xplore
In the early 1970s, MOS IC technology enabled the very large-scale integration, integration of more than 10,000 transistors on a single chip. System on a Chip (SoCs) are complete computers on a microchip (or chip) the size of a coin. They may or may not have integrated random-access memory, 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 don't 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 portable computer, mobile computers were heavy and ran from mains power. The 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 s and tablet computer, tablets run on a variety of operating systems and recently became the dominant computing device on the market. These are powered by System on a Chip (SoCs), which are complete computers on a microchip the size of a coin.


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) * Server ** Server (computing), Rackmount server ** Blade server ** Computer tower, Tower server * Personal computer ** Workstation ** Microcomputer (term no longer used) *** Home computer (term fallen into disuse) ** Desktop computer *** Computer tower, Tower desktop *** Slimline desktop **** Multimedia computer (non-linear editing system computers, video editing PCs and the like, this term is no longer used) **** Gaming computer *** All-in-one PC *** Nettop (Small form factor (desktop and motherboard), Small form factor PCs, Mini PCs) *** Home theater PC *** Keyboard computer *** Portable computer *** Thin client *** Internet appliance ** Laptop *** Desktop replacement computer *** Gaming computer#Gaming laptop computers, Gaming laptop *** Rugged computer, Rugged laptop *** 2-in-1 PC *** Ultrabook *** Chromebook *** Subnotebook *** Netbook * Mobile computing, 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


The term ''hardware'' covers all of those parts of a computer that are tangible physical objects. Electrical network, 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

Other hardware topics

A general-purpose computer has four main components: the
arithmetic logic unit In computing, an arithmetic logic unit (ALU) is a Combinational logic, combinational digital circuit that performs arithmetic and bitwise operations on integer binary numbers. This is in contrast to a floating-point unit (FPU), which operates on ...
(ALU), the control unit, the Computer data storage, memory, and the input and output devices (collectively termed I/O). These parts are interconnected by bus (computing), buses, often made of groups of
wire Overhead power cabling. The conductor consists of seven strands of steel (centre, high tensile strength), surrounded by four outer layers of aluminium (high conductivity). Sample diameter 40 mm A wire is a flexible strand of metal A me ...

s. Inside each of these parts are thousands to trillions of small electrical network, electrical circuits which can be turned off or on by means of an transistor, 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 * Computer mouse, 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 (computing), 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. Control systems in advanced computers may change the order of execution of some instructions to improve performance. A key component common to all CPUs is the program counter, a special memory cell (a processor register, register) that keeps track of which location in memory the next instruction is to be read from. 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: # Read the code for the next instruction from the cell indicated by the program counter. # Decode the numerical code for the instruction into a set of commands or signals for each of the other systems. # Increment the program counter so it points to the next instruction. # 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. # Provide the necessary data to an ALU or register. # If the instruction requires an ALU or specialized hardware to complete, instruct the hardware to perform the requested operation. # Write the result from the ALU back to a memory location or to a register or perhaps an output device. # 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 A central processing unit (CPU), also called a central processor, main processor or just Processor (computing), processor, is the electronic circuitry that executes Instruction (computing), instructions comprising a computer program. The CPU per ...

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 ''''.

Arithmetic logic unit (ALU)

The ALU is capable of performing two classes of operations: arithmetic and logic. The set of arithmetic operations that a particular ALU supports may be limited to addition and subtraction, or might include multiplication, division,
trigonometry Trigonometry () is a branch of mathematics that studies relationships between side lengths and angles of triangles. The field emerged in the Hellenistic period, Hellenistic world during the 3rd century BC from applications of geometry to Astr ...

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 Truth value, 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: logical conjunction, AND, logical disjunction, OR, Exclusive or, XOR, and Negation, NOT. These can be useful for creating complicated conditional (programming), conditional statements and processing Boolean logic. Superscalar computers may contain multiple ALUs, allowing them to process several instructions simultaneously. Graphics processing unit, Graphics processors and computers with Single instruction, multiple data, SIMD and Multiple instruction, multiple data, MIMD features often contain ALUs that can perform arithmetic on Euclidean vector, vectors and Matrix (mathematics), matrices.


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. 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 Processor register, 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 system, 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. In more sophisticated computers there may be one or more RAM CPU cache, 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. Devices that provide input or output to the computer are called peripherals. On a typical personal computer, peripherals include input devices like the keyboard and Computer mouse, mouse, and output devices such as the computer monitor, display and printer (computing), 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, with their own CPU and memory. A graphics processing unit might contain fifty or more tiny computers that perform the calculations necessary to display 3D computer graphics, 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.


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. 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. 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 (computing), 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.


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 server (computing), 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 architectures that differ significantly from the basic stored-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 Computer simulation, simulation, Rendering (computer graphics), graphics rendering, and cryptography applications, as well as with other so-called "embarrassingly parallel" tasks.


''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 from which the system is built. Computer software includes computer programs, Library (computing), libraries and related non-executable Data (computing), data, such as Software documentation, 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 Read-only memory, ROM in an IBM PC compatible computer, it is sometimes called "firmware".


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


The defining feature of modern computers which distinguishes them from all other machines is that they can be computer programming, programmed. That is to say that some type of Instruction (computer science), instructions (the Computer program, 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 (FLOPS, 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 Computer data storage, memory and are generally carried out (execution (computing), executed) in the order they were given. However, there are usually specialized instructions to tell the computer to jump ahead or backwards to some other place in the program and to carry on executing from there. These are called "jump" instructions (or Branch (computer science), branches). Furthermore, jump instructions may be made to happen conditional (programming), 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 control flow, 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 architecture, MIPS assembly language: begin: addi $8, $0, 0 # initialize sum to 0 addi $9, $0, 1 # set first number to add = 1 loop: slti $10, $9, 1000 # check if the number is less than 1000 beq $10, $0, finish # if odd number is greater than n then exit add $8, $8, $9 # update sum addi $9, $9, 1 # get next number j loop # repeat the summing process finish: add $2, $8, $0 # 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. 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 code, machine language) and while this technique was used with many early computers, 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 Assembly language#Assembler, assembler before being run, or translated directly at run time by an interpreter (computing), interpreter. Sometimes programs are executed by a hybrid method of the two techniques.

= Low-level languages

= 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 or a handheld video game, hand-held videogame) cannot understand the machine language of an x86 CPU that might be in a Personal computer, PC. 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 high-level 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. 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. As problems become larger and more complex, features such as subprograms, modules, formal documentation, and new paradigms such as object-oriented programming are encountered. Large programs involving thousands of line of code and more require formal software methodologies. The task of developing large Computer software, software systems presents a significant intellectual challenge. Producing software with an acceptably high reliability within a predictable schedule and budget has historically been difficult; the academic and professional discipline of software engineering concentrates specifically on this challenge.


Errors in computer programs are called "Software bug, 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 (computing), hang", becoming unresponsive to input such as Computer mouse, mouse clicks or keystrokes, to completely fail, or to Crash (computing), crash. Otherwise benign bugs may sometimes be harnessed for malicious intent by an unscrupulous user writing an Exploit (computer security), 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 nearly always the result of programmer error or an oversight made in the program's design. Admiral Grace Hopper, an American 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.

Networking and the Internet

Computers have been used to coordinate information between multiple locations since the 1950s. The U.S. military's Semi-Automatic Ground Environment, 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 (computer system), Sabre. 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. 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 Asymmetric digital subscriber line, 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.

Unconventional computers

A computer does not need to be electronics, electronic, nor even have a Central processing unit, processor, nor Random-access memory, RAM, nor even a hard disk. While popular usage of the word "computer" is synonymous with a personal electronic computer, 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." According to this definition, any device that ''processes information'' qualifies as a computer.


There is active research to make computers out of many promising new types of technology, such as optical computing, optical computers, DNA computing, DNA computers, wetware computer, neural computers, and quantum computing, 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 Shor's algorithm, 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. Logic gates are a common abstraction which can apply to most of the above digital or analog signal, 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 Turing-complete, 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 pattern-based systems include Speech recognition, 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. 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.

See also

* Glossary of computers * 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 pioneers in computer science * Pulse computation * TOP500 (list of most powerful computers) * Unconventional computing




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External links

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Warhol & The Computer
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