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A computer is a
machine A machine is a physical system using Power (physics), power to apply Force, forces and control Motion, movement to perform an action. The term is commonly applied to artificial devices, such as those employing engines or motors, but also to na ...
that can be programmed to carry out sequences of
arithmetic Arithmetic () is an elementary part of 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 chang ...
or
logical operations In logic Logic is the study of correct reasoning. It includes both Mathematical logic, formal and informal logic. Formal logic is the science of Validity (logic), deductively valid inferences or of logical truths. It is a formal science i ...
(
computation Computation is any type of arithmetic or non-arithmetic calculation that follows a well-defined model (e.g., an algorithm). Mechanical or electronic devices (or, History of computing hardware, historically, people) that perform computations are ...
) automatically. Modern
digital electronic Digital electronics is a field of electronics involving the study of digital signals and the engineering of devices that use or produce them. This is in contrast to analog electronics and analog signals. Digital electronic circuits are usually ...
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 An operating system (OS) is system software that manages computer hardware, software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ef ...
(main
software Software is a set of computer programs and associated software documentation, documentation and data (computing), data. This is in contrast to Computer hardware, hardware, from which the system is built and which actually performs the work. ...
), and
peripheral A peripheral or peripheral device is an auxiliary device used to put information into and get information out of a computer. The term ''peripheral device'' refers to all hardware components that are attached to a computer and are controlled by the ...
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 A computer network is a set of computers sharing resources located on or provided by Node (networking), network nodes. The computers use common communication protocols over digital signal, digital interconnections to communicate with each ot ...
or
computer cluster A computer cluster is a set of computers that work together so that they can be viewed as a single system. Unlike Grid computing, grid computers, computer clusters have each Node (networking), node set to perform the same task, controlled and ...
. A broad range of industrial and
consumer products A final good or consumer good is a final product ready for sale that is used by the consumer to satisfy current wants or needs, unlike a intermediate good, which is used to produce other goods. A microwave oven or a bicycle is a final good, but t ...
use computers as
control system A control system manages, commands, directs, or regulates the behavior of other devices or systems using control loops. It can range from a single home heating controller using a thermostat controlling a domestic boiler to large industrial co ...
s. Simple special-purpose devices like
microwave oven A microwave oven (commonly referred to as a microwave) is an electric oven that heats and cooks food by exposing it to electromagnetic spectrum, electromagnetic radiation in the microwave frequency range. This induces Dipole#Molecular dipoles, ...
s and
remote control In electronics, a remote control (also known as a remote or clicker) is an electronic device used to operate another device from a distance, usually wirelessly. In consumer electronics, a remote control can be used to operate devices such as ...
s are included, as are factory devices like
industrial robot An industrial robot is a robot system used for manufacturing. Industrial robots are automated, programmable and capable of movement on three or more axes. Typical applications of robots include welding Welding is a fabrication process t ...
s and
computer-aided design Computer-aided design (CAD) is the use of computers (or ) to aid in the creation, modification, analysis, or optimization of a design. This software is used to increase the productivity of the designer, improve the quality of design, improve co ...
, as well as general-purpose devices like
personal computer A personal computer (PC) is a multi-purpose microcomputer whose size, capabilities, and price make it feasible for individual use. Personal computers are intended to be operated directly by an end user, rather than by a computer expert or techn ...
s and
mobile device A mobile device (or handheld computer) is a computer small enough to hold and operate in the hand. Mobile devices typically have a flat LCD or OLED screen, a touchscreen interface, and digital or physical buttons. They may also have a physical k ...
s like
smartphone A smartphone is a Mobile device, portable computer device that combines Mobile phone, mobile telephone and Mobile computing, computing functions into one unit. They are distinguished from feature phones by their stronger hardware capabilities ...
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
abacus The abacus (''plural'' abaci or abacuses), also called a counting frame, is a calculating tool which has been used since Ancient history, ancient times. It was used in the ancient Near East, Europe, China, and Russia, centuries before the ado ...
have aided people in doing calculations since ancient times. Early in the
Industrial Revolution The Industrial Revolution was the transition to new manufacturing processes in Great Britain, continental Europe, and the United States, that occurred during the period from around 1760 to about 1820–1840. This transition included going fr ...
, some mechanical devices were built to automate long, tedious tasks, such as guiding patterns for
loom A loom is a device used to weaving, weave cloth and tapestry. The basic purpose of any loom is to hold the Warp (weaving), warp threads under tension (mechanics), tension to facilitate the interweaving of the weft threads. The precise shape o ...
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 World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...
. The first
semiconductor A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...
transistor file:MOSFET Structure.png, upright=1.4, Metal-oxide-semiconductor field-effect transistor (MOSFET), showing Metal gate, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink). A ...
s in the late 1940s were followed by the
silicon Silicon is a chemical element with the Symbol (chemistry), symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a Tetravalence, tetravalent metalloid and semiconductor. It is a member ...
-based
MOSFET The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a type of field-effect transistor (FET), most commonly fabricated by the controlled oxidation of silicon. It has an insulated gate, the voltage of which ...
(MOS transistor) and
monolithic integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuit An electronic circuit is composed of individual electronic components, such as resistors, transistor ...
chip technologies in the late 1950s, leading to the
microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circu ...
and the
microcomputer revolution The history of the personal computer as a mass-market consumer electronic device began with the microcomputer revolution of the 1970s. A personal computer is one intended for interactive individual use, as opposed to a mainframe computer where ...
in the 1970s. The speed, power and versatility of computers have been increasing dramatically ever since then, with
transistor count The transistor count is the number of transistors in an electronic device (typically on a single substrate or "chip"). It is the most common measure of integrated circuit complexity (although the majority of transistors in modern microprocessors ...
s increasing at a rapid pace (as predicted by
Moore's law Moore's law is the observation that the Transistor count, number of transistors in a dense integrated circuit (IC) doubles about every two years. Moore's law is an observation and Forecasting, projection of a historical trend. Rather than a la ...
), leading to the Digital Revolution during the late 20th to early 21st centuries. Conventionally, a modern computer consists of at least one
processing element This glossary of computer hardware terms is a list of definitions of terms and concepts related to computer hardware, i.e. the physical and structural components of computers, architectural issues, and peripheral devices. A ...
, 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 ...
(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 Printer may refer to: Technology * Printer (publishing) In publishing, printers are both companies providing printing Printing is a process for mass reproducing text and Printmaking, images using a master form or template. The ear ...
, 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.


Etymology

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 ...
''".


History


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 ...
with
fingers A finger is a limb of the body and a type of digit, an organ of manipulation and sensation Sensation (psychology) refers to the processing of the senses by the sensory system. Sensation or sensations may also refer to: In arts and entert ...
. 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 ...
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
abacus The abacus (''plural'' abaci or abacuses), also called a counting frame, is a calculating tool which has been used since Ancient history, ancient times. It was used in the ancient Near East, Europe, China, and Russia, centuries before the ado ...
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 ...
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 ...
and
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 Khwarazm Khwarazm (; Old Persian Old Persian is one of the two directly attested Old Iranian languages (the other being Avestan languag ...
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 ...
.
The
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
machine A machine is a physical system using Power (physics), power to apply Force, forces and control Motion, movement to perform an action. The term is commonly applied to artificial devices, such as those employing engines or motors, but also to na ...
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 ...
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
planimeter A planimeter, also known as a platometer, is a measuring instrument A measuring instrument is a device to measurement, measure a physical quantity. In the physical sciences, quality assurance, and engineering, measurement is the activity of ob ...
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 ...
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 ...
, 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 Pierre Jaquet-Droz (; 1721–1790) was a watchmaker of the late eighteenth century. He was born on 28 July 1721 in La Chaux-de-Fonds, in the Principality of Neuchâtel, which was then part of the Kingdom of Prussia The Kingdom of Prussia ...
, 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 devised a 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 ...
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 A tide-predicting machine was a special-purpose 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 networ ...
invented by the Scottish scientist
Sir William Thomson William Thomson, 1st Baron Kelvin, (26 June 182417 December 1907) was a British mathematician, Mathematical physics, mathematical physicist and engineer born in Belfast. Professor of Natural Philosophy (Glasgow), Professor of Natural Philoso ...
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 ...
s by
integration Integration may refer to: Biology * Multisensory integration * Path integration * Pre-integration complex The pre-integration complex (PIC) is a nucleoprotein complex of viral genetic material and associated viral and host proteins which is capa ...
, 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 integrator The ball-and-disk integrator is a key component of many advanced 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 c ...
s.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 ...
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 ...
, 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 ...
, 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 ...
s, a method being used at the time to direct mechanical
loom A loom is a device used to weaving, weave cloth and tapestry. The basic purpose of any loom is to hold the Warp (weaving), warp threads under tension (mechanics), tension to facilitate the interweaving of the weft threads. The precise shape o ...
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 ...
. 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 computer science, control flow (or flow of control) is the order in which individual statements, instructions or function calls of an imperative program are executed or evaluated. The emphasis on explicit control flow distinguishes an ' ...
in the form of
conditional branching In computer science Computer science is the study of computation, automation, and information. Computer science spans theoretical disciplines (such as algorithms, theory of computation, information theory, and automation) to Applied sci ...
and loops, and integrated
memory Memory is the faculty of the mind by which data or information is Encoding (memory), encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If Foresight (psycholo ...
, making it the first design for a general-purpose computer that could be described in modern terms as
Turing-complete In computability theory, a system of data-manipulation rules (such as a computer's instruction set In computer science Computer science is the study of computation, automation, and information. Computer science spans theoretical di ...
. 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 ga, Rialtas a Shoilse gd, Riaghaltas a Mhòrachd , image = HM Government logo.svg , image_size = 220px , image2 = Royal Coat of Arms of the United Kingdom (HM Government).svg , image_size2 = 180px , caption = Royal coat of arms of t ...
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 Computing is any goal-oriented activity requiring, benefiting from, or creating computer, computing machinery. It includes the study and experimentation of algorithmic processes, and development of both computer hardware , hardware and software. ...
needs were met by increasingly sophisticated analog computers, which used a direct mechanical or electrical model of the problem as a basis for
computation Computation is any type of arithmetic or non-arithmetic calculation that follows a well-defined model (e.g., an algorithm). Mechanical or electronic devices (or, History of computing hardware, historically, people) that perform computations are ...
. 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 A tide-predicting machine was a special-purpose 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 networ ...
, invented by
Sir William Thomson William Thomson, 1st Baron Kelvin, (26 June 182417 December 1907) was a British mathematician, Mathematical physics, mathematical physicist and engineer born in Belfast. Professor of Natural Philosophy (Glasgow), Professor of Natural Philoso ...
(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, the elder brother of the more famous Sir William Thomson. The art of mechanical analog computing reached its zenith with the
differential analyzer The differential analyser is a mechanical analogue computer An analog computer or analogue computer is a type of computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations (c ...
, 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 ...
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 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 ...
) and aircraft (
control system A control system manages, commands, directs, or regulates the behavior of other devices or systems using control loops. It can range from a single home heating controller using a thermostat controlling a domestic boiler to large industrial co ...
s).


Digital computers


Electromechanical

By 1938, the
United States Navy The United States Navy (USN) is the maritime military branch, service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the es ...
had developed an electromechanical analog computer small enough to use aboard a
submarine A submarine (or sub) is a watercraft capable of independent operation underwater. It differs from a submersible, which has more limited underwater capability. The term is also sometimes used historically or colloquially to refer to remotely op ...
. 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 World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...
similar devices were developed in other countries as well. Early digital computers were
electromechanical In engineering Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. The discipline of engineering encompasses a broad ran ...
; 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 tube A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied. The type kn ...
s. The Z2, created by German engineer
Konrad Zuse Konrad Ernst Otto Zuse (; 22 June 1910 – 18 December 1995) was a German civil engineer, List of pioneers in computer science, pioneering computer scientist, inventor and businessman. His greatest achievement was the world's first programmab ...
in 1939, was one of the earliest examples of an electromechanical relay computer. In 1941, Zuse followed his earlier machine up with the Z3, the world's first working electromechanical programmable, fully automatic digital computer. The Z3 was built with 2000
relay file:Delta Electronics DPS-350FB A - board 1 - OEG SDT-SS-112M - case removed-3045.jpg, A relay file:Kontakt.svg, Electromechanical relay schematic showing a control coil, four pairs of normally open and one pair of normally closed contacts file:R ...
s, implementing a 22 bit
word length In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computer, computing machinery. It includes the study and experimentation of algorithmic processes, and development of both computer hardware , hardwa ...
that operated at a
clock frequency In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computer, computing machinery. It includes the study and experimentation of algorithmic processes, and development of both computer hardware , hardw ...
of about 5–10 Hz. Program code was supplied on punched
film A film also called a movie, motion picture, moving picture, picture, photoplay or (slang) flick is a work of visual art that simulates experiences and otherwise communicates ideas, stories, perceptions, feelings, beauty, or atmosphere ...
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 number In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computer, computing machinery. It includes the study and experimentation of algorithmic processes, and development of both computer hardware , hard ...
s. 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 ...
's earlier design), using a
binary Binary may refer to: Science and technology Mathematics * Binary number A binary number is a number expressed in the base-2 numeral system or binary numeral system, a method of mathematical expression which uses only two symbols: typical ...
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 Alan Mathison Turing (; 23 June 1912 – 7 June 1954) was an English mathematician, computer scientist, logician, cryptanalysis, cryptanalyst, philosopher, and mathematical and theoretical biology, theoretical biologist. Turing was high ...
. 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 (colloquially) , former_name = eidgenössische polytechnische Schule , image = ETHZ.JPG , image_size = , established = , type = Public , budget = CHF 1.896 billion (2021) , rector = Günther Dissertori , president = Joël Mesot , ...
. 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 An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or Conductive trace, traces through which electric current can flow. It is a t ...
elements soon replaced their mechanical and electromechanical equivalents, at the same time that digital calculation replaced analog. The engineer
Tommy Flowers Thomas Harold Flowers MBE (22 December 1905 – 28 October 1998) was an English engineer with the British General Post Office. During World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a wor ...
, working at the
Post Office Research Station The Post Office Research Station was first established as a separate section of the General Post Office in 1909. In 1921, the Research Station moved to Dollis Hill, north west London, initially in ex-army huts. The main permanent buildings at ...
in
London London is the capital and List of urban areas in the United Kingdom, largest city of England and the United Kingdom, with a population of just under 9 million. It stands on the River Thames in south-east England at the head of a estuary dow ...
in the 1930s, began to explore the possible use of electronics for the
telephone exchange A telephone exchange, telephone switch, or central office is a telecommunications system used in the public switched telephone network (PSTN) or in large enterprises. It interconnects telephone subscriber lines or virtual circuits of digital syst ...
. Experimental equipment that he built in 1934 went into operation five years later, converting a portion of the
telephone exchange A telephone exchange, telephone switch, or central office is a telecommunications system used in the public switched telephone network (PSTN) or in large enterprises. It interconnects telephone subscriber lines or virtual circuits of digital syst ...
network into an electronic data processing system, using thousands of
vacuum tube A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied. The type kn ...
s. In the US,
John Vincent Atanasoff John Vincent Atanasoff, , (October 4, 1903 – June 15, 1995) was an American physicist A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scal ...
and Clifford E. Berry of
Iowa State University Iowa State University of Science and Technology (Iowa State University, Iowa State, or ISU) is a Public university, public land-grant university, land-grant research university in Ames, Iowa. Founded in 1858 as the Iowa Agricultural College and ...
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 Bletchley Park is an English country house and estate in Bletchley, Milton Keynes (Buckinghamshire) that became the principal centre of Allies of World War II, Allied World War II cryptography, code-breaking during the Second World War. The man ...
achieved a number of successes at breaking encrypted German military communications. The German encryption machine,
Enigma Enigma may refer to: *Riddle, someone or something that is mysterious or puzzling Biology *ENIGMA, a class of gene in the LIM domain Computing and technology *Enigma (company), a New York-based data-technology startup *Enigma machine, a family of ...
, was first attacked with the help of the electro-mechanical
bombe The bombe () was an electro-mechanical In engineering, electromechanics combines processes and procedures drawn from electrical engineering and mechanical engineering. Electromechanics focuses on the interaction of electrical and mechani ...
s 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 Maxwell Herman Alexander Newman, FRS, (7 February 1897 – 22 February 1984), generally known as Max Newman, was a British mathematician A mathematician is someone who uses an extensive knowledge of mathematics in their work, typically t ...
and his colleagues commissioned Flowers to build the Colossus. He spent eleven months from early February 1943 designing and building the first Colossus. After a functional test in December 1943, Colossus was shipped to Bletchley Park, where it was delivered on 18 January 1944 and attacked its first message on 5 February. Colossus was the world's first
electronic Electronic may refer to: *Electronics, the science of how to control electric energy in semiconductor *Electronics (magazine), ''Electronics'' (magazine), a defunct American trade journal *Electronic storage, the storage of data using an electroni ...
digital programmable computer. It used a large number of valves (vacuum tubes). It had paper-tape input and was capable of being configured to perform a variety of
boolean logic 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 ...
al operations on its data, but it was not
Turing-complete In computability theory, a system of data-manipulation rules (such as a computer's instruction set In computer science Computer science is the study of computation, automation, and information. Computer science spans theoretical di ...
. 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 ENIAC (; Electronic Numerical Integrator and Computer) was the first Computer programming, programmable, Electronics, electronic, general-purpose digital computer, completed in 1945. There were other computers that had these features, but the ...
(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 In computability theory, a system of data-manipulation rules (such as a computer's instruction set In computer science Computer science is the study of computation, automation, and information. Computer science spans theoretical di ...
. 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 A stored-program computer is a computer that stores Instruction (computer science), program instructions in electronically or optically accessible memory. This contrasts with systems that stored the program instructions with plugboards or simila ...
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 John William Mauchly (August 30, 1907 – January 8, 1980) was an American physicist who, along with J. Presper Eckert, designed ENIAC, the first general-purpose electronic digital computer, as well as EDVAC, BINAC and UNIVAC I, the first com ...
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 Alan Mathison Turing (; 23 June 1912 – 7 June 1954) was an English mathematician, computer scientist, logician, cryptanalyst, philosopher, and theoretical biologist. Turing was highly influential in the development of theoretical ...
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 In computer science, a universal Turing machine (UTM) is a Turing machine that can simulate an arbitrary Turing machine on arbitrary input. The universal machine essentially achieves this by reading both the description of the machine to be simu ...
. 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 A stored-program computer is a computer that stores Instruction (computer science), program instructions in electronically or optically accessible memory. This contrasts with systems that stored the program instructions with plugboards or simila ...
, where all the instructions for computing are stored in memory.
Von Neumann Von Neumann may refer to: * John von Neumann John von Neumann (; hu, Neumann János Lajos, ; December 28, 1903 – February 8, 1957) was a Hungarian-American mathematician, physicist, computer scientist, engineer and polymath. He w ...
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 In theoretical computer science and mathematics, the theory of computation is the branch that deals with what problems can be solved on a model of computation, using an algorithm, how algorithmic efficiency, efficiently they can be solved or t ...
. Except for the limitations imposed by their finite memory stores, modern computers are said to be
Turing-complete In computability theory, a system of data-manipulation rules (such as a computer's instruction set In computer science Computer science is the study of computation, automation, and information. Computer science spans theoretical di ...
, which is to say, they have
algorithm In mathematics and computer science, an algorithm () is a finite sequence of rigorous instructions, typically used to solve a class of specific Computational problem, problems or to perform a computation. Algorithms are used as specificat ...
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 In computer science Computer science is the study of computation, automation, and information. Computer science spans theoretical disciplines (such as algorithms, theory of computation, information theory, and automation) to Applied sci ...
and can store in memory a set of instructions (a program) that details the
computation Computation is any type of arithmetic or non-arithmetic calculation that follows a well-defined model (e.g., an algorithm). Mechanical or electronic devices (or, History of computing hardware, historically, people) that perform computations are ...
. The theoretical basis for the stored-program computer was laid out by
Alan Turing Alan Mathison Turing (; 23 June 1912 – 7 June 1954) was an English mathematician, computer scientist, logician, cryptanalyst, philosopher, and theoretical biologist. Turing was highly influential in the development of theoretical ...
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 The University of Pennsylvania (also known as Penn or UPenn) is a Private university, private research university in Philadelphia. It is the fourth-oldest institution of higher education in the United States and is ranked among the highest- ...
also circulated his ''
First Draft of a Report on the EDVAC The ''First Draft of a Report on the EDVAC'' (commonly shortened to ''First Draft'') is an incomplete 101-page document written by John von Neumann John von Neumann (; hu, Neumann János Lajos, ; December 28, 1903 – February 8, ...
'' in 1945. The
Manchester Baby The Manchester Baby, also called the Small-Scale Experimental Machine (SSEM), was the first electronic stored-program computer. It was built at the University of Manchester by Frederic Calland Williams, Frederic C. Williams, Tom Kilburn, and Ge ...
was the world's first
stored-program computer A stored-program computer is a computer that stores Instruction (computer science), program instructions in electronically or optically accessible memory. This contrasts with systems that stored the program instructions with plugboards or simila ...
. It was built at the
University of Manchester The University of Manchester is a public university, public research university in Manchester, England. The main campus is south of Manchester city centre, Manchester City Centre on Wilmslow Road, Oxford Road. The university owns and operates majo ...
in England by Frederic C. Williams,
Tom Kilburn Tom Kilburn (11 August 1921 – 17 January 2001) was an English mathematician A mathematician is someone who uses an extensive knowledge of mathematics in their work, typically to solve mathematical problems. Mathematicians are concerned ...
and
Geoff Tootill Geoff C. Tootill (4 March 1922 – 26 October 2017) was an electronic engineer Electronics engineering is a sub-discipline of electrical engineering which emerged in the early 20th century and is distinguished by the additional use of active ...
, and ran its first program on 21 June 1948. It was designed as a
testbed A testbed (also spelled test bed) is a platform for conducting rigorous, transparent, and replicable testing of scientific theories, computational tools, and new technologies. The term is used across many disciplines to describe experimental rese ...
for the
Williams tube The Williams tube, or the Williams–Kilburn tube named after inventors Frederic Calland Williams, Freddie Williams and Tom Kilburn, is an early form of computer memory. It was the first Random-access memory, random-access digital storage devic ...
, the first random-access digital storage device. Although the computer was described as "small and primitive" by a 1998 retrospective, it was the first working machine to contain all of the elements essential to a modern electronic computer. As soon as the Baby had demonstrated the feasibility of its design, a project began at the university to develop it into a practically useful computer, the
Manchester Mark 1 The Manchester Mark 1 was one of the earliest stored-program computers, developed at the Victoria University of Manchester, England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It shares la ...
. The Mark 1 in turn quickly became the prototype for the
Ferranti Mark 1 The Ferranti Mark 1, also known as the Manchester Electronic Computer in its sales literature, and thus sometimes called the Manchester Ferranti, was produced by British electrical engineering firm Ferranti, Ferranti Ltd. It was the world's fir ...
, the world's first commercially available general-purpose computer. Built by
Ferranti Ferranti or Ferranti International plc was a UK electrical engineering Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems which use electricity, electron ...
, 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 Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses ** Thin-shell structure Science Biology * Seashell, a hard out ...
labs in
Amsterdam Amsterdam ( , , , lit. ''The Dam on the River Amstel'') is the Capital of the Netherlands, capital and Municipalities of the Netherlands, most populous city of the Netherlands, with The Hague being the seat of government. It has a population ...
. 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 Cambridge ( ) is a College town, university city and the county town in Cambridgeshire, England. It is located on the River Cam approximately north of London. As of the 2021 United Kingdom census, the population of Cambridge was 145,700. Cam ...
EDSAC The Electronic Delay Storage Automatic Calculator (EDSAC) was an early British computer. Inspired by John von Neumann's seminal ''First Draft of a Report on the EDVAC'', the machine was constructed by Maurice Wilkes and his team at the Universit ...
of 1949, became operational in April 1951 and ran the world's first routine office computer job.
Grace Hopper Grace Brewster Hopper (; December 9, 1906 – January 1, 1992) was an American computer scientist, mathematician, and United States Navy Rear admiral (United States), rear admiral. One of the first programmers of the Harvard Mark I, Harvard Mar ...
was the first to develop a
compiler In computing, a compiler is a computer program that Translator (computing), translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily ...
for a programming language.


Transistors

The concept of a
field-effect transistor The field-effect transistor (FET) is a type of transistor that uses an electric field to control the flow of Electric current, current in a semiconductor. FETs (JFETs or MOSFETs) are devices with three terminals: ''source'', ''gate'', and ''dra ...
was proposed by
Julius Edgar Lilienfeld Julius Edgar Lilienfeld (April 18, 1882 – August 28, 1963) was an Austro-Hungarian, and later American (where he moved in 1921) physicist and electrical engineer, who was credited with the first patent on the field effect (semiconductor), f ...
in 1925.
John Bardeen John Bardeen (; May 23, 1908 – January 30, 1991) was an American physicist and engineer. He is the only person to be awarded the Nobel Prize in Physics twice: first in 1956 with William Shockley and Walter Houser Brattain, Walter Brattain for t ...
and
Walter Brattain Walter Houser Brattain (; February 10, 1902 – October 13, 1987) was an American physicist at Bell Labs who, along with fellow scientists John Bardeen and William Shockley, invented the point-contact transistor in December 1947. They shared the ...
, while working under
William Shockley William Bradford Shockley Jr. (February 13, 1910 – August 12, 1989) was an American physicist and inventor. He was the manager of a research group at Bell Labs that included John Bardeen and Walter Houser Brattain, Walter Brattain. The three ...
at
Bell Labs Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984), then AT&T Bell Laboratories (1984–1996) and Bell Labs Innovations (1996–2007), is an American industrial research and scientific development company A com ...
, built the first working
transistor file:MOSFET Structure.png, upright=1.4, Metal-oxide-semiconductor field-effect transistor (MOSFET), showing Metal gate, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink). A ...
, the
point-contact transistor The point-contact transistor was the first type of transistor to be successfully demonstrated. It was developed by research scientists John Bardeen and Walter Houser Brattain, Walter Brattain at Bell Laboratories in December 1947. They worked in ...
, in 1947, which was followed by Shockley's
bipolar junction transistor A bipolar junction transistor (BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. In contrast, a unipolar transistor, such as a field-effect transistor, uses only one kind of charge carrier. A bipolar t ...
in 1948. From 1955 onwards, transistors replaced
vacuum tube A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied. The type kn ...
s 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 Mass production, also known as flow production or continuous production, is the production of substantial amounts of standardized products in a constant flow, including and especially on assembly lines. Together with job production and batch ...
basis, which limited them to a number of specialised applications. At the
University of Manchester The University of Manchester is a public university, public research university in Manchester, England. The main campus is south of Manchester city centre, Manchester City Centre on Wilmslow Road, Oxford Road. The university owns and operates majo ...
, a team under the leadership of
Tom Kilburn Tom Kilburn (11 August 1921 – 17 January 2001) was an English mathematician A mathematician is someone who uses an extensive knowledge of mathematics in their work, typically to solve mathematical problems. Mathematicians are concerned ...
designed and built a machine using the newly developed transistors instead of valves. 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 Drum memory was a magnetic data storage device invented by Gustav Tauschek in 1932 in Austria. Drums were widely used in the 1950s and into the 1960s as computer memory. For many early computers, drum memory formed the main working memory of ...
, 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 The Atomic Energy Research Establishment (AERE) was the main Headquarters, centre for nuclear power, atomic energy research and development in the United Kingdom from 1946 to the 1990s. It was created, owned and funded by the British Governm ...
at Harwell. The metal–oxide–silicon field-effect transistor (MOSFET), also known as the MOS transistor, was invented by
Mohamed M. Atalla Mohamed M. Atalla ( ar, محمد عطاالله; August 4, 1924 – December 30, 2009) was an Egyptian-American engineer, physicist A physicist is a scientist who specializes in the field of physics, which encompasses the interactions o ...
and
Dawon Kahng Dawon Kahng ( ko, 강대원; May 4, 1931 – May 13, 1992) was a Korean-American electrical engineer and inventor, known for his work in solid-state electronics. He is best known for inventing the MOSFET (metal–oxide–semiconductor field-effe ...
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 high scalability, and much lower power consumption and higher density than bipolar junction transistors, the MOSFET made it possible to build high-density integrated circuits. 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 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 Magnetic-core memory was the predominant form of random access, random-access computer memory for 20 years between about 1955 and 1975. Such memory is often just called core memory, or, informally, core. Core memory uses toroids (rings) of a ...
in computers. The MOSFET led to the
microcomputer revolution The history of the personal computer as a mass-market consumer electronic device began with the microcomputer revolution of the 1970s. A personal computer is one intended for interactive individual use, as opposed to a mainframe computer where ...
, 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 Digital electronics is a field of electronics involving the study of digital signals and the engineering of devices that use or produce them. This is in contrast to analog electronics and analog signals. Digital electronic circuits are usually ...
.


Integrated circuits

The next great advance in computing power came with the advent of the
integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of ti ...
(IC). The idea of the integrated circuit was first conceived by a radar scientist working for the
Royal Radar Establishment The Royal Radar Establishment was a Science park, research centre in Malvern, Worcestershire in the United Kingdom. It was formed in 1953 as the Radar Research Establishment by the merger of the Air Ministry's Telecommunications Research Establi ...
of the
Ministry of Defence {{unsourced, date=February 2021 A ministry of defence or defense (see spelling differences), also known as a department of defence or defense, is an often-used name for the part of a government A government is the system or group o ...
, 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. The first working ICs were invented by
Jack Kilby Jack St. Clair Kilby (November 8, 1923 – June 20, 2005) was an American electrical engineer who took part (along with Robert Noyce of Fairchild Semiconductor, Fairchild) in the realization of the first integrated circuit while working at Texa ...
at
Texas Instruments Texas Instruments Incorporated (TI) is an American technology company headquartered in Dallas, Texas, that designs and manufactures semiconductors and various integrated circuits, which it sells to electronics designers and manufacturers globall ...
and
Robert Noyce Robert Norton Noyce (December 12, 1927 – June 3, 1990), nicknamed "the Mayor of Silicon Valley", was an American physicist and entrepreneur who co-founded Fairchild Semiconductor in 1957 and Intel Corporation Intel Corporation is an ...
at
Fairchild Semiconductor Fairchild Semiconductor International, Inc. was an American semiconductor company based in San Jose, California. Founded in 1957 as a division of Fairchild Camera and Instrument, it became a pioneer in the manufacturing of transistors and of ...
. 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 A hybrid integrated circuit (HIC), hybrid microcircuit, hybrid circuit or simply hybrid is a miniaturized electronic circuit constructed of individual devices, such as semiconductor devices (e.g. transistors, diodes or Integrated circuits, mon ...
(hybrid IC), rather than a
monolithic integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuit An electronic circuit is composed of individual electronic components, such as resistors, transistor ...
(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
silicon Silicon is a chemical element with the Symbol (chemistry), symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a Tetravalence, tetravalent metalloid and semiconductor. It is a member ...
, whereas Kilby's chip was made of
germanium Germanium is a chemical element with the Symbol (chemistry), symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid in the carbon group that is chemically similar to it ...
. Noyce's monolithic IC was fabricated using the
planar process The planar process is a manufacturing process used in the semiconductor industry The semiconductor industry is the aggregate of companies engaged in the Electronic design automation, design and Fabrication (semiconductor), fabrication of semi ...
, developed by his colleague
Jean Hoerni Jean Amédée Hoerni (September 26, 1924 – January 12, 1997) was a Swiss-American engineer. He was a silicon transistor pioneer, and a member of the "traitorous eight". He developed the planar process, an important technology for reliably Semic ...
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
MOSFET The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a type of field-effect transistor (FET), most commonly fabricated by the controlled oxidation of silicon. It has an insulated gate, the voltage of which ...
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 The RCA Corporation was a major American electronics company, which was founded as the Radio Corporation of America in 1919. It was initially a patent pool, patent trust owned by General Electric (GE), Westinghouse Electric Corporation, Westin ...
in 1962.
General Microelectronics General Micro-electronics (GMe) was an American semiconductor company in the 1960s. It was formed by three former members of Fairchild Semiconductor, and is thus one of the "Fairchildren". It was acquired in 1966 by Philco-Ford and became their Mic ...
later introduced the first commercial MOS IC in 1964, developed by Robert Norman. Following the development of the
self-aligned gate In Semiconductor device fabrication, semiconductor electronics fabrication technology, a self-aligned gate is a transistor manufacturing approach whereby the gate (transistor), gate electrode of a MOSFET (metal–oxide–semiconductor field-effec ...
(silicon-gate) MOS transistor by Robert Kerwin, Donald Klein and John Sarace at Bell Labs in 1967, the first
silicon-gate In Semiconductor device fabrication, semiconductor electronics fabrication technology, a self-aligned gate is a transistor manufacturing approach whereby the gate (transistor), gate electrode of a MOSFET (metal–oxide–semiconductor field-effec ...
MOS IC with
self-aligned gate In Semiconductor device fabrication, semiconductor electronics fabrication technology, a self-aligned gate is a transistor manufacturing approach whereby the gate (transistor), gate electrode of a MOSFET (metal–oxide–semiconductor field-effec ...
s was developed by
Federico Faggin Federico Faggin (, ; born 1 December 1941) is an Italian physicist, engineer, inventor and entrepreneur. He is best known for designing the first commercial microprocessor, the Intel 4004. He led the Intel 4004, 4004 (MCS-4) project and the desi ...
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
microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circu ...
, 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 The Intel 4004 is a 4-bit computing, 4-bit central processing unit (CPU) released by Intel, Intel Corporation in 1971. Sold for US$60, it was the first commercially produced microprocessor, and the first in a List of Intel microprocessors, long ...
, designed and realized by Federico Faggin with his silicon-gate MOS IC technology, along with Ted Hoff,
Masatoshi Shima is a Japanese Electronic engineering, electronics engineer. He was one of the architects of the world's first microprocessor, the Intel 4004. In 1968, Shima worked for Busicom in Japan, and did the logic design for a specialized CPU to be transl ...
and Stanley Mazor at
Intel Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California, Santa Clara, California. It is the world's largest semiconductor chip manufacturer by revenue, and is one of the devel ...
.
Federico Faggin Federico Faggin (, ; born 1 December 1941) is an Italian physicist, engineer, inventor and entrepreneur. He is best known for designing the first commercial microprocessor, the Intel 4004. He led the Intel 4004, 4004 (MCS-4) project and the desi ...

The Making of the First Microprocessor
, ''IEEE Solid-State Circuits Magazine'', Winter 2009,
IEEE Xplore IEEE Xplore digital library is a research database for discovery and access to journal articles, conference proceedings, technical standards, and related materials on computer science, electrical engineering and electronics, and allied fields. It ...
In the early 1970s, MOS IC technology enabled the
integration Integration may refer to: Biology * Multisensory integration * Path integration * Pre-integration complex The pre-integration complex (PIC) is a nucleoprotein complex of viral genetic material and associated viral and host proteins which is capa ...
of more than 10,000 transistors on a single chip.
System on a Chip A system on a chip or system-on-chip (SoC ; pl. ''SoCs'' ) is an integrated circuit that integrates most or all components of a computer or other Electronics, electronic system. These components almost always include a central processing unit ( ...
(SoCs) are complete computers on a
microchip An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Transistor count, Large ...
(or chip) the size of a coin. They may or may not have integrated
RAM Ram, ram, or RAM may refer to: Animals * A male sheep Sheep or domestic sheep (''Ovis aries'') are domesticated, ruminant mammals typically kept as livestock. Although the term ''sheep'' can apply to other species in the genus ''Ovis'', in ...
and
flash memory Flash memory is an Integrated circuit, electronic Non-volatile memory, non-volatile computer memory storage medium that can be electrically erased and reprogrammed. The two main types of flash memory, NOR flash and NAND flash, are named for t ...
. If not integrated, the RAM is usually placed directly above (known as
Package on package Package on a package (PoP) is an integrated circuit packaging method to vertically combine discrete logic and memory ball grid array (BGA) packages. Two or more packages are installed atop each other, i.e. stacked, with a standard interface to rout ...
) or below (on the opposite side of the
circuit board A printed circuit board (PCB; also printed wiring board or PWB) is a medium used in Electrical engineering, electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a L ...
) 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
mobile computers Mobile computing is human–computer interaction in which a computer is expected to be transported during normal usage, which allows for the transmission of data, voice, and video. Mobile computing involves mobile communication, mobile hardware ...
were heavy and ran from mains power. The
IBM 5100 The IBM 5100 Portable Computer is a portable computer (one of the first) introduced in September 1975, six years before the IBM Personal Computer, and eight before the first successful IBM compatible portable computer, the Compaq Portable. It ...
was an early example. Later portables such as the
Osborne 1 The Osborne 1 is the first commercially successful portable computer, released on April 3, 1981 by Osborne Computer Corporation. It weighs , cost US$1,795, and runs the CP/M 2.2 operating system. It is powered from a AC power plugs and sockets, w ...
and
Compaq Portable The Compaq Portable was an early portable computer A portable computer is a computer designed to be easily moved from one place to another and included a Computer monitor, display and Keyboard technology, keyboard together, with a single ...
were considerably lighter but still needed to be plugged in. The first
laptop A laptop, laptop computer, or notebook computer is a small, portable personal computer (PC) with a screen and alphanumeric keyboard. Laptops typically have a Flip (form), clam shell Form factor (design), form factor with the computer scr ...
s, such as the
Grid Compass The Grid Compass (written ''GRiD'' by its manufacturer GRiD Systems Corporation) is one of the first laptop computer A laptop, laptop computer, or notebook computer is a small, portable personal computer (PC) with a screen and alpha ...
, 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
smartphone A smartphone is a Mobile device, portable computer device that combines Mobile phone, mobile telephone and Mobile computing, computing functions into one unit. They are distinguished from feature phones by their stronger hardware capabilities ...
s and 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 A system on a chip or system-on-chip (SoC ; pl. ''SoCs'' ) is an integrated circuit that integrates most or all components of a computer or other Electronics, electronic system. These components almost always include a central processing unit ( ...
(SoCs), which are complete computers on a microchip the size of a coin.


Types

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


By architecture

*
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 ...
*
Digital computer A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as C ...
*
Hybrid computer Hybrid computers are computers that exhibit features of analog computers and digital computers. The digital component normally serves as the controller and provides logical and Numerical analysis, numerical operations, while the analog component ...
*
Harvard architecture The Harvard architecture is a computer architecture with separate computer storage, storage and signal pathways for Machine code, instructions and data. It contrasts with the von Neumann architecture, where program instructions and data share ...
*
Von Neumann architecture The von Neumann architecture — also known as the von Neumann model or Princeton architecture — is a computer architecture based on a 1945 description by John von Neumann, and by others, in the ''First Draft of a Report on the EDVAC''. The ...
*
Complex instruction set computer A complex instruction set computer (CISC ) is a computer architecture In computer engineering, computer architecture is a description of the structure of a computer system made from component parts. It can sometimes be a high-level description ...
*
Reduced instruction set computer In computer engineering, a reduced instruction set computer (RISC) is a computer designed to simplify the individual instructions given to the computer to accomplish tasks. Compared to the instructions given to a complex instruction set comput ...


By size, form-factor and purpose

*
Supercomputer A supercomputer is a computer with a high level of performance as compared to a general-purpose computer. The performance of a supercomputer is commonly measured in floating-point operations per second (FLOPS) instead of million instructions p ...
*
Mainframe computer A mainframe computer, informally called a mainframe or big iron, is a computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital ele ...
*
Minicomputer A minicomputer, or colloquially mini, is a class of smaller general purpose computers that developed in the mid-1960s and sold at a much lower price than Mainframe computer, mainframe and mid-size computers from IBM and BUNCH, its direct competi ...
(term no longer used) * Server ** Rackmount server **
Blade server A blade server is a stripped-down server computer with a modular design optimized to minimize the use of physical space and energy. Blade servers have many components removed to save space, minimize power consumption and other considerations, whil ...
** Tower server *
Personal computer A personal computer (PC) is a multi-purpose microcomputer whose size, capabilities, and price make it feasible for individual use. Personal computers are intended to be operated directly by an end user, rather than by a computer expert or techn ...
**
Workstation A workstation is a special computer designed for technical or computational science, scientific applications. Intended primarily to be used by a single user, they are commonly connected to a local area network and run multi-user operating syste ...
**
Microcomputer A microcomputer is a small, relatively inexpensive computer having a central processing unit (CPU) made out of a microprocessor. The computer also includes Computer memory, memory and input/output (I/O) circuitry together mounted on a printed ...
(term no longer used) *** Home computer (term fallen into disuse) **
Desktop computer A desktop computer (often abbreviated desktop) is a personal computer designed for regular use at a single location on or near a desk due to its size and power requirements. The most common configuration has a computer case, case that houses th ...
*** Tower desktop *** Slimline desktop **** Multimedia computer (
non-linear editing system Non-linear editing is a form of offline editing for Audio editing, audio, Video editing, video, and image editing. In offline editing, the original content is not modified in the course of editing. In non-linear editing, edits are specified an ...
computers, video editing PCs and the like, this term is no longer used) **** Gaming computer ***
All-in-one PC An all-in-one computer or all-in-one PC (AIO) is a personal computer that integrates the system's internal components into the same case as the display, thus occupying a smaller footprint (with fewer cables) than desktop computer, desktops that in ...
***
Nettop A nettop (or miniature PC, Mini PC or Smart Micro PC) is a small-sized, inexpensive, low-power, Legacy free PC, legacy-free desktop computer, desktop computer designed for basic tasks such as Web navigation, web browsing, accessing web applicat ...
( Small form factor PCs, Mini PCs) ***
Home theater PC A home theater PC (HTPC) or media center computer is a technological convergence, convergent device that combines some or all the capabilities of a personal computer with a software application that focuses on video, photo, audio playback, and ...
***
Keyboard computer A keyboard computer is a computer which contains all of the regular components of a personal computer A personal computer (PC) is a multi-purpose microcomputer whose size, capabilities, and price make it feasible for individual use. Personal ...
***
Portable computer A portable computer is a computer designed to be easily moved from one place to another and included a Computer monitor, display and Keyboard technology, keyboard together, with a single plug, much like later desktop computers called ''Desk ...
***
Thin client In computer networking, a thin client is a simple (low-Computer performance, performance) computer that has been Program optimization, optimized for Remote desktop, establishing a remote connection with a Server (computing), server-based comp ...
***
Internet appliance An Internet appliance is a consumer device whose main function is easy access to Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communica ...
**
Laptop A laptop, laptop computer, or notebook computer is a small, portable personal computer (PC) with a screen and alphanumeric keyboard. Laptops typically have a Flip (form), clam shell Form factor (design), form factor with the computer scr ...
***
Desktop replacement computer A desktop replacement computer (DTR) is a personal computer that provides the full capabilities of a desktop computer while remaining Mobile computing, mobile. They are often larger, bulkier laptops or in some cases 2-in-1 PCs with a Tablet compu ...
*** Gaming laptop *** Rugged laptop ***
2-in-1 PC A 2-in-1 PC, also known as convertible laptop, 2-in-1 tablet, 2-in-1 laptop, 2-in-1 detachable, laplet, tabtop, laptop tablet, or simply 2-in-1, is a portable computer that has features of both tablet computer, tablets and laptops. Before the e ...
***
Ultrabook Ultrabook is a marketing term, originated and trademarked by Intel, for a category of high-end laptop computers. They were originally marketed as featuring ultra thin form factor and light weight design without compromising battery life or perf ...
***
Chromebook A Chromebook (sometimes stylized in lowercase as chromebook) is a laptop or tablet running the Linux-based ChromeOS as its operating system. Initially designed to heavily rely on web applications for tasks using the Google Chrome browser, Chromeb ...
***
Subnotebook Subnotebook, also called ultraportable, superportable, or mini notebook, was a marketing term for laptop computers that are smaller and lighter than a typical notebook-sized laptop. Types and sizes As typical laptop sizes have decreased over t ...
***
Netbook Netbook was a commonly used term that identified a product class of small and inexpensive laptop computer, laptops which were sold from 2007 to around 2013. These machines were designed primarily as cost-effective tools for consumers to ...
*
Mobile computers Mobile computing is human–computer interaction in which a computer is expected to be transported during normal usage, which allows for the transmission of data, voice, and video. Mobile computing involves mobile communication, mobile hardware ...
: **
Tablet computer A tablet computer, commonly shortened to tablet, is a mobile device, typically with a mobile operating system and touchscreen display processing circuitry, and a rechargeable battery in a single, thin and flat package. Tablets, being comput ...
**
Smartphone A smartphone is a Mobile device, portable computer device that combines Mobile phone, mobile telephone and Mobile computing, computing functions into one unit. They are distinguished from feature phones by their stronger hardware capabilities ...
**
Ultra-mobile PC An ultra-mobile PC, or ultra-mobile personal computer (UMPC), is a miniature version of a Pen computing, pen computer, a class of laptop whose specifications were launched by Microsoft and Intel in spring 2006. Sony had already made a first att ...
**
Pocket PC A Pocket PC (P/PC, PPC) is a class of personal digital assistant (PDA) that runs the Windows Mobile or Windows Embedded Compact operating system that has some of the abilities of modern desktop IBM PC compatible, PCs. The name was introduced by ...
**
Palmtop PC A handheld personal computer (PC) is a miniature computer typically built around a clamshell form factor and is significantly smaller than any standard laptop A laptop, laptop computer, or notebook computer is a small, portable pers ...
**
Handheld PC A handheld personal computer (PC) is a miniature computer typically built around a clamshell form factor and is significantly smaller than any standard laptop A laptop, laptop computer, or notebook computer is a small, portable pers ...
*
Wearable computer A wearable computer, also known as a body-borne computer, is a computing device worn on the body. The definition of 'wearable computer' may be narrow or broad, extending to smartphones or even ordinary wristwatches. Wearables may be for general ...
**
Smartwatch A smartwatch is a wearable computer in the form of a watch; modern smartwatches provide a local touchscreen interface for daily use, while an associated smartphone app provides management and telemetry, such as long-term biomonitoring. While ea ...
**
Smartglasses Smartglasses or smart glasses are eye or head-worn wearable computer, wearable computers that offer useful capabilities to the user. Many smartglasses include displays that add information alongside or to what the wearer sees. Alternatively, sm ...
*
Single-board computer A single-board computer (SBC) is a complete computer built on a single circuit board, with microprocessor(s), random-access memory, memory, input/output (I/O) and other features required of a functional computer. Single-board computers are common ...
*
Plug computer A plug computer is an external device, often configured for use in the home A home, or domicile, is a space used as a permanent or semi-permanent residence for one or many humans, and sometimes various pet, companion animals. It is a f ...
*
Stick PC A stick PC or PC on a stick is a single-board computer in a small elongated casing resembling a stick, that can usually be plugged directly (without an HDMI cable) into an HDMI video port. A stick PC is a device which has independent CPUs or proce ...
*
Programmable logic controller A programmable logic controller (PLC) or programmable controller is an industrial computer that has been Rugged computer, ruggedized and adapted for the control of manufacturing processes, such as assembly lines, machines, robotic devices, or ...
*
Computer-on-module A computer-on-module (COM) is a type of single-board computer (SBC), a subtype of an embedded computer system. An extension of the concept of System on a chip, system on chip (SoC) and system in package (SiP), COM lies between a full-up computer ...
*
System on module A system on a module (SoM) is a board-level circuit that integrates a system function in a single module. It may integrate digital and analog functions on a single board. A typical application is in the area of embedded systems. Unlike a sing ...
*
System in a package A system in a package (SiP) or system-in-package is a number of integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small fla ...
*
System-on-chip A system on a chip or system-on-chip (SoC ; pl. ''SoCs'' ) is an integrated circuit that integrates most or all components of a computer or other Electronics, electronic system. These components almost always include a central processing unit ( ...
(Also known as an Application Processor or AP if it lacks circuitry such as radio circuitry) *
Microcontroller A microcontroller (MCU for ''microcontroller unit'', often also MC, UC, or μC) is a small computer on a single VLSI integrated circuit (IC) chip. A microcontroller contains one or more Central processing unit, CPUs (processor cores) along with ...


Hardware

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


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 control unit (CU) is a component of a computer's central processing unit (CPU) that directs the operation of the processor. A CU typically uses a binary decoder to convert coded instructions into timing and control signals that direct the ope ...
, the
memory Memory is the faculty of the mind by which data or information is Encoding (memory), encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If Foresight (psycholo ...
, and the input and output devices (collectively termed I/O). These parts are interconnected by
buses A bus (contracted from omnibus, with variants multibus, motorbus, autobus, etc.) is a road vehicle that carries significantly more passengers than an average car or van. It is most commonly used in public transport, but is also in use for char ...
, 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 circuits An electrical network is an interconnection of electronic component, electrical components (e.g., battery (electricity), batteries, resistors, inductors, capacitors, switches, transistors) or a model of such an interconnection, consisting of e ...
which can be turned off or on by means of an
electronic switch In electronics, an electronic switch is an electronic component or device that can switch an electrical circuit, interrupting the Electric current, current or diverting it from one conductor to another. Electronic switches are considered binary de ...
. 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 gate A logic gate is an idealized or physical device implementing a Boolean function, a logical operation performed on one or more Binary number, binary inputs that produces a single binary output. Depending on the context, the term may refer to an id ...
s 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 A computer keyboard is a peripheral input device modeled after the typewriter keyboard which uses an arrangement of buttons or Push-button, keys to act as Mechanical keyboard, mechanical levers or Electronic switching system, electronic switche ...
*
Digital camera A digital camera is a camera that captures photographs in digital memory. Most cameras produced today are digital, largely replacing those that capture images on photographic film. Digital cameras are now widely incorporated into mobile devices ...
*
Digital video Digital video is an electronic representation of moving visual images (video) in the form of encoded digital data. This is in contrast to analog video, which represents moving visual images in the form of analog signals. Digital video comprises ...
*
Graphics tablet A graphics tablet (also known as a digitizer, digital graphic tablet, pen tablet, drawing tablet, external drawing pad or digital art board) is a computer input device that enables a user to hand-draw images, animations and graphics, with a spec ...
*
Image scanner An image scanner—often abbreviated to just scanner—is a device that optically scans images, printed text, handwriting or an object and converts it to a digital image. Commonly used in offices are variations of the desktop ''flatbed scanner'' w ...
*
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 ...
*
Microphone A microphone, colloquially called a mic or mike (), is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and public ...
*
Mouse A mouse (plural, : mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus mus ...
*
Overlay keyboard An overlay keyboard or concept keyboard is a specialized keyboard with no preset keys. Each key can be programmed with a wide range of different functions. Overlay keyboards are often used as a quick and easy way to input items with just two butto ...
*
Real-time clock A real-time clock (RTC) is an electronic device (most often in the form of an integrated circuit) that measures the passage of time. Although the term often refers to the devices in personal computers, server (computing), servers and embedded ...
*
Trackball A trackball is a pointing device consisting of a ball held by a socket containing sensors to detect a rotation of the ball about two axes—like an upside-down ball mouse (computing), mouse with an exposed protruding ball. Users roll the ball t ...
*
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 ...
*
Light pen A light pen is a computer input device in the form of a light-sensitive wand used in conjunction with a computer's cathode-ray tube (CRT) display. It allows the user to point to displayed objects or draw on the screen in a similar way to a tou ...


Output devices

The means through which computer gives output are known as output devices. Some examples of output devices are: *
Computer monitor A computer monitor is an output device that displays information in pictorial or textual form. A discrete monitor comprises a electronic visual display, visual display, support electronics, power supply, Housing (engineering), housing, electric ...
*
Printer Printer may refer to: Technology * Printer (publishing) In publishing, printers are both companies providing printing Printing is a process for mass reproducing text and Printmaking, images using a master form or template. The ear ...
*
PC speaker A PC speaker is a loudspeaker A loudspeaker (commonly referred to as a speaker or speaker driver) is an Acoustical engineering#Electroacoustics, electroacoustic transducer that converts an electrical audio signal into a corresponding soun ...
*
Projector A projector or image projector is an optical device that projects an image (or moving images) onto a surface, commonly a projection screen. Most projectors create an image by shining a light through a small transparent lens, but some newer types ...
*
Sound card A sound card (also known as an audio card) is an internal expansion card that provides input and output of audio signals to and from a computer under the control of computer programs. The term ''sound card'' is also applied to external audio i ...
*
Video card A graphics card (also called a video card, display card, graphics adapter, VGA card/VGA, video adapter, display adapter, or mistakenly GPU) is an expansion card which generates a feed of output images to a display device, such as a computer moni ...


Control unit

The
control unit The control unit (CU) is a component of a computer's central processing unit (CPU) that directs the operation of the processor. A CU typically uses a binary decoder to convert coded instructions into timing and control signals that direct the ope ...
(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 The program counter (PC), commonly called the instruction pointer (IP) in Intel x86 and Itanium microprocessors, and sometimes called the instruction address register (IAR), the instruction counter, or just part of the instruction sequencer, is ...
, a special memory cell (a
register Register or registration may refer to: Arts entertainment, and media Music * Register (music) A register is the "height" or range of a note, set of pitches or pitch classes, melody A melody (from Greek language, Greek μελῳ ...
) 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 In computer science, control flow (or flow of control) is the order in which individual statements, instructions or function calls of an imperative program are executed or evaluated. The emphasis on explicit control flow distinguishes an ' ...
). The sequence of operations that the control unit goes through to process an instruction is in itself like a short
computer program A computer program is a sequence or set of instructions in a programming language for a computer to Execution (computing), execute. Computer programs are one component of software, which also includes software documentation, documentation and oth ...
, and indeed, in some more complex CPU designs, there is another yet smaller computer called a
microsequencer In computer architecture In computer engineering, computer architecture is a description of the structure of a computer system made from component parts. It can sometimes be a high-level description that ignores details of the implementation. At a ...
, which runs a
microcode In processor design, microcode (μcode) is a technique that interposes a layer of computer organization between the central processing unit (CPU) hardware and the programmer-visible instruction set architecture of a computer. Microcode is a laye ...
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 ...
(CPU). Early CPUs were composed of many separate components. Since the 1970s, CPUs have typically been constructed on a single
MOS integrated circuit file:MOSFET Structure.png, upright=1.6, MOSFET, showing metal gate, gate (G), body (B), source (S), and drain (D) terminals. The gate is separated from the body by an gate oxide, insulating layer (pink). The metal–oxide–semiconductor field- ...
chip called a ''
microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circu ...
''.


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 root In mathematics, a square root of a number is a number such that ; in other words, a number whose ''square (algebra), square'' (the result of multiplying the number by itself, or  ⋅ ) is . For example, 4 and −4 are square roots o ...
s. Some can operate only on whole numbers (
integer An integer is the number zero (), a positive natural number (, , , etc.) or a negative integer with a minus sign (−1, −2, −3, etc.). The negative numbers are the additive inverses of the corresponding positive numbers. In the language of ...
s) while others use
floating point In computing, floating-point arithmetic (FP) is arithmetic that represents real numbers approximately, using an Integer (computer science), integer with a fixed precision, called the significand, scaled by an integer exponent of a fixed base. ...
to represent
real number In mathematics, a real number is a number that can be used to measurement, measure a ''continuous'' one-dimensional quantity such as a distance, time, duration or temperature. Here, ''continuous'' means that values can have arbitrarily small var ...
s, 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 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 ...
: AND, OR, XOR, and NOT. These can be useful for creating complicated conditional statements and processing
Boolean logic 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 ...
.
Superscalar A superscalar processor is a CPU that implements a form of parallelism called instruction-level parallelism Instruction-level parallelism (ILP) is the Parallel computing, parallel or simultaneous execution of a sequence of Instruction set, ...
computers may contain multiple ALUs, allowing them to process several instructions simultaneously. Graphics processors and computers with
SIMD Single instruction, multiple data (SIMD) is a type of parallel computer, parallel processing in Flynn's taxonomy. SIMD can be internal (part of the hardware design) and it can be directly accessible through an instruction set architecture (IS ...
and
MIMD In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computer, computing machinery. It includes the study and experimentation of algorithmic processes, and development of both computer hardware , hardwa ...
features often contain ALUs that can perform arithmetic on vectors and
matrices Matrix most commonly refers to: * The Matrix (franchise), ''The Matrix'' (franchise), an American media franchise ** ''The Matrix'', a 1999 science-fiction action film ** "The Matrix", a fictional setting, a virtual reality environment, within Th ...
.


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. In almost all modern computers, each memory cell is set up to store
binary number A binary number is a number expressed in the base-2 numeral system or binary numeral system, a method of mathematical expression which uses only two symbols: typically "0" (zero) and "1" (one). The base-2 numeral system is a positional notation ...
s in groups of eight bits (called a
byte The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable un ...
). 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 Two's complement is a mathematical operation to reversibly convert a positive binary number into a negative binary number with equivalent (but negative) value, using the Most Significant Bit, binary digit with the greatest place value (the leftmos ...
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 Random-access memory (RAM; ) is a form of computer memory that can be read and changed in any order, typically used to store working Data (computing), data and machine code. A Random access, random-access memory device allows data items to b ...
or RAM *
read-only memory Read-only memory (ROM) is a type of non-volatile memory used in computers and other electronic devices. Data stored in ROM cannot be electronically modified after the manufacture of the memory device. Read-only memory is useful for storing soft ...
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 In computing, BIOS (, ; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is firmware used to provide runtime services for operating systems and programs and to perform Computer hardware, hardware initializ ...
that orchestrates loading the computer's
operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ef ...
from the hard disk drive into RAM whenever the computer is turned on or reset. In
embedded computers An embedded system is a computer system A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can ...
, 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 In computing, firmware is a specific class of computer software that provides the High- and low-level, low-level control for a device's specific Computer hardware, hardware. Firmware, such as the BIOS of a personal computer, may contain basic fun ...
, because it is notionally more like hardware than software.
Flash memory Flash memory is an Integrated circuit, electronic Non-volatile memory, non-volatile computer memory storage medium that can be electrically erased and reprogrammed. The two main types of flash memory, NOR flash and NAND flash, are named for t ...
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 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
peripheral A peripheral or peripheral device is an auxiliary device used to put information into and get information out of a computer. The term ''peripheral device'' refers to all hardware components that are attached to a computer and are controlled by the ...
s. On a typical personal computer, peripherals include input devices like the keyboard and
mouse A mouse (plural, : mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus mus ...
, and output devices such as the display and
printer Printer may refer to: Technology * Printer (publishing) In publishing, printers are both companies providing printing Printing is a process for mass reproducing text and Printmaking, images using a master form or template. The ear ...
.
Hard disk drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating hard disk platter, platters ...
s,
floppy disk A floppy disk or floppy diskette (casually referred to as a floppy, or a diskette) is an obsolescent type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined wi ...
drives and
optical disc drive In computing, an optical disc drive is a disk drive, disc drive that uses laser light or electromagnetic waves within or near the visible light spectrum as part of the process of reading or writing data to or from optical discs. Some drives ...
s serve as both input and output devices.
Computer network A computer network is a set of computers sharing resources located on or provided by Node (networking), network nodes. The computers use common communication protocols over digital signal, digital interconnections to communicate with each ot ...
ing 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 A graphics processing unit (GPU) is a specialized electronic circuit designed to manipulate and alter memory (computing), memory to accelerate the creation of Digital image, images in a frame buffer intended for output to a display device. GPUs ...
might contain fifty or more tiny computers that perform the calculations necessary to display
3D graphics 3D computer graphics, or “3D graphics,” sometimes called CGI, 3D-CGI or three-dimensional Computer-generated imagery, computer graphics are graphics that use a three-dimensional representation of geometric data (often Cartesian coordinate ...
. Modern
desktop computer A desktop computer (often abbreviated desktop) is a personal computer designed for regular use at a single location on or near a desk due to its size and power requirements. The most common configuration has a computer case, case that houses th ...
s 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. One means by which this is done is with a special signal called an
interrupt In digital computers, an interrupt (sometimes referred to as a trap) is a request for the processor to ''interrupt'' currently executing code (when permitted), so that the event can be processed in a timely manner. If the request is accepted ...
, 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 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
supercomputer A supercomputer is a computer with a high level of performance as compared to a general-purpose computer. The performance of a supercomputer is commonly measured in floating-point operations per second (FLOPS) instead of million instructions p ...
s,
mainframe computer A mainframe computer, informally called a mainframe or big iron, is a computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital ele ...
s and servers. Multiprocessor and
multi-core A multi-core processor is a microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor ...
(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
simulation A simulation is the imitation of the operation of a real-world process or system over time. Simulations require the use of Conceptual model, models; the model represents the key characteristics or behaviors of the selected system or proc ...
, graphics rendering, and
cryptography Cryptography, or cryptology (from grc, , translit=kryptós "hidden, secret"; and ''graphein'', "to write", or ''-logy, -logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of ...
applications, as well as with other so-called "
embarrassingly parallel In parallel computing Parallel computing is a type of computing, computation in which many calculations or Process (computing), processes are carried out simultaneously. Large problems can often be divided into smaller ones, which can then be s ...
" 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 program A computer program is a sequence or set of instructions in a programming language for a computer to Execution (computing), execute. Computer programs are one component of software, which also includes software documentation, documentation and oth ...
s,
libraries A library is a collection of Document, materials, books or media that are accessible for use and not just for display purposes. A library provides physical (hard copies) or electronic media, digital access (soft copies) materials, and may be a ...
and related non-executable
data In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interp ...
, such as online documentation or
digital media Digital media is any media (communication), communication media that operate in conjunction with various encoded machine-readable data formats. Digital media can be created, viewed, distributed, modified, listened to, and preserved on a digital ...
. It is often divided into
system software System software is software designed to provide a platform for other software. Examples of system software include operating systems (OS) like macOS, Linux, Android and Microsoft Windows, computational science software, game engines, search engin ...
and
application software An application program (software application, or application, or app for short) is a computer program designed to carry out a specific task other than one relating to the operation of the computer itself, typically to be used by end user, end-user ...
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 In computing, BIOS (, ; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is firmware used to provide runtime services for operating systems and programs and to perform Computer hardware, hardware initializ ...
ROM Rom, or ROM may refer to: Biomechanics and medicine * Risk of mortality The risk of mortality (ROM) provides a medical classification to estimate the likelihood of inhospital death for a patient. The ROM classes are minor, moderate, major, and e ...
in an
IBM PC compatible IBM PC compatible computers are similar to the original IBM Personal Computer, IBM PC, IBM Personal Computer XT, XT, and IBM Personal Computer/AT, AT, all from computer giant IBM, that are able to use the same software and expansion cards. Such ...
computer, it is sometimes called "firmware".


Languages

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


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 The von Neumann architecture — also known as the von Neumann model or Princeton architecture — is a computer architecture based on a 1945 description by John von Neumann, and by others, in the ''First Draft of a Report on the EDVAC''. The ...
often have machine code in the form of an
imperative programming language In computer science Computer science is the study of computation, automation, and information. Computer science spans theoretical disciplines (such as algorithms, theory of computation, information theory, and automation) to Applied scien ...
. 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 processor A word processor (WP) is a device or computer program that provides for input, editing, formatting, and output of text, often with some additional features. Early word processors were stand-alone devices dedicated to the function, but current ...
s and
web browser A web browser is application software for accessing websites. When a User (computing), user requests a web page from a particular website, the browser retrieves its Computer file, files from a web server and then displays the page on the user' ...
s 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
programmer A computer programmer, sometimes referred to as a software developer, a software engineer, a programmer or a coder, is a person who creates computer software, computer programs — often for larger computer software. A programmer is someone ...
s 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 In computer science, random-access machine (RAM) is an abstract machine in the general class of register machines. The RAM is very similar to the counter machine but with the added capability of 'indirect addressing' of its registers. Like the cou ...
–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 Memory is the faculty of the mind by which data or information is Encoding (memory), encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If Foresight (psycholo ...
and are generally carried out (
executed Capital punishment, also known as the death penalty, is the State (polity), state-sanctioned practice of deliberately killing a person as a punishment for an actual or supposed crime, usually following an authorized, rule-governed process to ...
) 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
branches A branch, sometimes called a ramus in botany, is a woody structural member connected to the central trunk of a tree In botany, a tree is a perennial plant with an elongated Plant stem, stem, or trunk (botany), trunk, usually suppo ...
). Furthermore, jump instructions may be made to happen 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
subroutine In computer programming, a function or subroutine is a sequence of Instruction (computer science), program instructions that performs a specific task, packaged as a unit. This unit can then be used in programs wherever that particular task shou ...
s 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 An electronic calculator is typically a portable Electronics, electronic device used to perform calculations, ranging from basic arithmetic to complex mathematics. The first Solid-state electronics, solid-state electronic calculator was crea ...
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 # 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 In computer programming Computer programming is the process of performing a particular computation (or more generally, accomplishing a specific computing result), usually by designing and building an executable computer program. Programm ...
with each instruction being given a unique number (its operation code or
opcode In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computer, computing machinery. It includes the study and experimentation of algorithmic processes, and development of both computer hardware , hardw ...
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 The Harvard architecture is a computer architecture with separate computer storage, storage and signal pathways for Machine code, instructions and data. It contrasts with the von Neumann architecture, where program instructions and data share ...
after the
Harvard Mark I The Harvard Mark I, or IBM Automatic Sequence Controlled Calculator (ASCC), was a general-purpose electromechanical computer used in the war effort during the last part of World War II. One of the first programs to run on the Mark I was initia ...
computer. Modern von Neumann computers display some traits of the Harvard architecture in their designs, such as in
CPU cache A CPU cache is a hardware cache used by the central processing unit (CPU) of a computer to reduce the average cost (time or energy) to access data (computing), data from the main memory. A cache is a smaller, faster memory, located closer to a proc ...
s. While it is possible to write computer programs as long lists of numbers (
machine language In computer programming, machine code is any low-level programming language, consisting of machine language instruction set architecture, instructions, which are used to control a computer's central processing unit (CPU). Each instruction cau ...
) 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 A mnemonic ( ) device, or memory device, is any learning technique that aids information retention or retrieval (remembering) in the human memory for better understanding. Mnemonics make use of elaborative encoding, retrieval cues, and imagery ...
such as ADD, SUB, MULT or JUMP. These mnemonics are collectively known as a computer's
assembly language In computer programming, assembly language (or assembler language, or symbolic machine code), often referred to simply as Assembly and commonly abbreviated as ASM or asm, is any low-level programming language with a very strong correspondence be ...
. 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 language In neuropsychology, linguistics, and philosophy of language, a natural language or ordinary language is any language that has linguistic evolution, evolved naturally in humans through use and repetition without conscious planning or premeditati ...
s, 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 In computer programming Computer programming is the process of performing a particular computation (or more generally, accomplishing a specific computing result), usually by designing and building an executable computer program. Programm ...
by a
compiler In computing, a compiler is a computer program that Translator (computing), translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily ...
or an
assembler Assembler may refer to: Arts and media * Nobukazu Takemura, avant-garde electronic musician, stage name Assembler * Assemblers, a fictional List of Star Wars races (A-E)#Assembler, race in the ''Star Wars'' universe * Assemblers, an alternative na ...
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

= 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 ARM (stylised in lowercase as arm, formerly an acronym for Advanced RISC Machines and originally Acorn RISC Machine) is a family of reduced instruction set computer (RISC) instruction set architectures for central processing unit, computer ...
CPU (such as may be found in a
smartphone A smartphone is a Mobile device, portable computer device that combines Mobile phone, mobile telephone and Mobile computing, computing functions into one unit. They are distinguished from feature phones by their stronger hardware capabilities ...
or a hand-held videogame) cannot understand the machine language of an x86 CPU that might be in a 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 language In computer science, a high-level programming language is a programming language with strong Abstraction (computer science), abstraction from the details of the computer. In contrast to low-level programming languages, it may use natural language ...
s that are able to express the needs of the
programmer A computer programmer, sometimes referred to as a software developer, a software engineer, a programmer or a coder, is a person who creates computer software, computer programs — often for larger computer software. A programmer is someone ...
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 In computing, a compiler is a computer program that Translator (computing), translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily ...
. 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 console A video game console is an electronic device that Input/output, outputs a video signal or image to display a video game that can be played with a game controller. These may be home video game console, home consoles, which are generally placed i ...
s.


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
software Software is a set of computer programs and associated software documentation, documentation and data (computing), data. This is in contrast to Computer hardware, hardware, from which the system is built and which actually performs the work. ...
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 Software engineering is a systematic engineering approach to software development. A software engineer is a person who applies the principles of software engineering to design, develop, maintain, test, and evaluate software, computer software. Th ...
concentrates specifically on this challenge.


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 Hang or Hanging may refer to: People * Choe Hang (disambiguation), various people * Luciano Hang (born 1962/1963), Brazilian billionaire businessman * Ren Hang (disambiguation), various people Law * Hanging, a form of capital punishment Arts ...
", becoming unresponsive to input such as
mouse A mouse (plural, : mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus mus ...
clicks or keystrokes, to completely fail, or to crash. Otherwise benign bugs may sometimes be harnessed for malicious intent by an unscrupulous user writing an
exploit Exploit means to take advantage of something (a person, situation, etc.) for one's own end, especially unethically or unjustifiably. Exploit can mean: *Exploitation of natural resources *Exploit (computer security) *Video game exploit *Exploitati ...
, 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 Grace Brewster Hopper (; December 9, 1906 – January 1, 1992) was an American computer scientist, mathematician, and United States Navy Rear admiral (United States), rear admiral. One of the first programmers of the Harvard Mark I, Harvard Mar ...
, an American computer scientist and developer of the first
compiler In computing, a compiler is a computer program that Translator (computing), translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily ...
, 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 The Harvard Mark II, also known as the Aiken Relay Calculator, was an electromechanical computer A mechanical computer is a computer built from machine, mechanical components such as levers and gears rather than electronics, electronic component ...
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 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 A sabre (French language, French: Help:IPA/French, sabʁ or saber in American English) is a type of backsword with a curved blade associated with the light cavalry of the Early Modern warfare, early modern and Napoleonic period, Napoleon ...
. 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 The Defense Advanced Research Projects Agency (DARPA) is a research and development agency of the United States Department of Defense responsible for the development of emerging technologies for use by the military. Originally known as the Adv ...
), and the
computer network A computer network is a set of computers sharing resources located on or provided by Node (networking), network nodes. The computers use common communication protocols over digital signal, digital interconnections to communicate with each ot ...
that resulted was called the
ARPANET The Advanced Research Projects Agency Network (ARPANET) was the first wide-area packet-switched network with distributed control and one of the first networks to implement the TCP/IP protocol suite. Both technologies became the technical fo ...
. 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 The World Wide Web (WWW), commonly known as the Web, is an information system enabling documents and other web resources to be accessed over the Internet. Documents and downloadable media are made available to the network through web se ...
, combined with the development of cheap, fast networking technologies like
Ethernet Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 198 ...
and
ADSL Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line (DSL) technology, a data communications technology that enables faster data transmission over Copper wire, copper telephone lines than a conventional voiceband modem ...
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
electronic Electronic may refer to: *Electronics, the science of how to control electric energy in semiconductor *Electronics (magazine), ''Electronics'' (magazine), a defunct American trade journal *Electronic storage, the storage of data using an electroni ...
, nor even have a
processor Processor may refer to: Computing Hardware * Processor (computing) **Central processing unit (CPU), the hardware within a computer that executes a program *** Microprocessor, a central processing unit contained on a single integrated circuit (I ...
, nor
RAM Ram, ram, or RAM may refer to: Animals * A male sheep Sheep or domestic sheep (''Ovis aries'') are domesticated, ruminant mammals typically kept as livestock. Although the term ''sheep'' can apply to other species in the genus ''Ovis'', in ...
, nor even a
hard disk A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating hard disk platter, platters ...
. 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 suallyelectronic 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.


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 Computable functions are the basic objects of study in recursion theory, computability theory. Computable functions are the formalized analogue of the intuitive notion of algorithm, algorithms, in the sense that a function is computable if there ex ...
, 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 architecture In computer engineering, computer architecture is a description of the structure of a computer system made from component parts. It can sometimes be a high-level description that ignores details of the implementation. At a more detailed level, the ...
s: *
Quantum computer Quantum computing is a type of computation Computation is any type of arithmetic or non-arithmetic calculation that follows a well-defined model (e.g., an algorithm). Mechanical or electronic devices (or, History of computing hardware, histor ...
vs. Chemical computer *
Scalar processor Scalar processors are a class of computer processor In computing and computer science, a processor or processing unit is an electrical component (circuit (computer science), digital circuit) that performs operations on an external data source, u ...
vs.
Vector processor In computing, a vector processor or array processor is a central processing unit (CPU) that implements an instruction set where its Instruction (computer science), instructions are designed to operate efficiently and effectively on large Array d ...
*
Non-Uniform Memory Access Non-uniform memory access (NUMA) is a 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, electroni ...
(NUMA) computers *
Register machine In mathematical logic Mathematical logic is the study of formal logic within 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 ...
vs.
Stack machine In computer science, computer engineering and programming language implementations, a stack machine is a computer processor or a virtual machine in which the primary interaction is moving short-lived temporary values to and from a push down Sta ...
*
Harvard architecture The Harvard architecture is a computer architecture with separate computer storage, storage and signal pathways for Machine code, instructions and data. It contrasts with the von Neumann architecture, where program instructions and data share ...
vs.
von Neumann architecture The von Neumann architecture — also known as the von Neumann model or Princeton architecture — is a computer architecture based on a 1945 description by John von Neumann, and by others, in the ''First Draft of a Report on the EDVAC''. The ...
* Cellular architecture Of all these
abstract machine An abstract machine is a computer science theoretical model that allows for a detailed and precise analysis of how a computer system functions. It is analogous to a Function (mathematics), mathematical function in that it receives inputs and produ ...
s, a quantum computer holds the most promise for revolutionizing computing.
Logic gate A logic gate is an idealized or physical device implementing a Boolean function, a logical operation performed on one or more Binary number, binary inputs that produces a single binary output. Depending on the context, the term may refer to an id ...
s 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
calculator An electronic calculator is typically a portable Electronics, electronic device used to perform calculations, ranging from basic arithmetic to complex mathematics. The first Solid-state electronics, solid-state electronic calculator was crea ...
s. The
Church–Turing thesis In computability theory, the Church–Turing thesis (also known as computability thesis, the Turing–Church thesis, the Church–Turing conjecture, Church's thesis, Church's conjecture, and Turing's thesis) is a thesis A thesis (plura ...
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 Netbook was a commonly used term that identified a product class of small and inexpensive laptop computer, laptops which were sold from 2007 to around 2013. These machines were designed primarily as cost-effective tools for consumers to ...
,
supercomputer A supercomputer is a computer with a high level of performance as compared to a general-purpose computer. The performance of a supercomputer is commonly measured in floating-point operations per second (FLOPS) instead of million instructions p ...
,
cellular automaton A cellular automaton (pl. cellular automata, abbrev. CA) is a discrete model of computation studied in automata theory. Cellular automata are also called cellular spaces, tessellation automata, homogeneous structures, cellular structures, tessel ...
, 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 Artificial intelligence (AI) is intelligence—perceiving, synthesizing, and inferring information—demonstrated by machines, as opposed to intelligence displayed by animal cognition, animals and human intelligence, humans. Example tasks in ...
and
machine learning Machine learning (ML) is a field of inquiry devoted to understanding and building methods that 'learn', that is, methods that leverage data to improve performance on some set of tasks. It is seen as a part of artificial intelligence. Machine ...
. Artificial intelligence based products generally fall into two major categories:
rule-based system In computer science, a rule-based system is used to store and manipulate knowledge to interpret information in a useful way. It is often used in artificial intelligence applications and research. Normally, the term ''rule-based system'' is appli ...
s and
pattern recognition Pattern recognition is the automated recognition of patterns and regularities in data. It has applications in statistical data analysis, signal processing, image analysis, information retrieval, bioinformatics, data compression, computer ...
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 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 Computability theory, also known as recursion theory, is a branch of mathematical logic, computer science, and the theory of computation that originated in the 1930s with the study of computable functions and Turing degrees. The field has since e ...
*
Computer security Computer security, cybersecurity (cyber security), or information technology security (IT security) is the protection of computer systems and computer network, networks from attack by malicious actors that may result in unauthorized informati ...
* Glossary of computer hardware terms *
History of computer science The history of computer science began long before the modern discipline of computer science, usually appearing in forms like mathematics or physics. Developments in previous centuries alluded to the discipline that we now know as computer science ...
* List of computer term etymologies *
List of computer system manufacturers A computer system A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of o ...
* List of fictional computers *
List of pioneers in computer science This is a list of people who made transformative breakthroughs in the creation, development and imagining of what computers could do. Pioneers : ''To arrange the list by date or person (ascending or descending), click that column's small "up-do ...
* Pulse computation *
TOP500 The TOP500 project ranks and details the 500 most powerful non- distributed computer systems in the world. The project was started in 1993 and publishes an updated list of the supercomputers twice a year. The first of these updates always coinc ...
(list of most powerful computers) *
Unconventional computing Unconventional computing is computing Computing is any goal-oriented activity requiring, benefiting from, or creating computer, computing machinery. It includes the study and experimentation of algorithmic processes, and development of both co ...


Notes


References


Sources

* * * * * * * * * * * * * * * * * * * * * * * * * * * *


External links

* *
Warhol & The Computer
(by Chris Garcia) at CHM {{Authority control Consumer electronics Articles containing video clips Articles with example code Electronics industry