View source for Computer

{{Short description|Programmable machine that processes data}}
{{Other uses|Computer (disambiguation)}}
{{Pp-semi-indef}}
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{{multiple image|perrow = 2|total_width=300
| image1 = ENIAC-changing a tube (cropped).jpg | alt1 = Black-and-white image of a man replacing one vacuum tube out of hundreds in early computer
| image2 = IBM System360 Mainframe.jpg | alt2 = Computer room with multiple computer cabinets and operating panel
| image3 = LYF WATER 2 Smartphone.JPG | alt3 = Smartphone with rainbow-like display held in a hand
| image4 = ThinkCentre S50.jpg | alt4 = Black desktop computer with monitor on top and keyboard in front
| image5 = Gamecube-console.jpg | alt5 = Purple video game console with attached controller
| image6 = Summit (supercomputer).jpg | alt6 = Rows of large, dark computer cabinets in warehouse-like room
| footer = Computers and computing devices from different eras—left to right, top to bottom:
{{bulleted list
|Early vacuum tube computer ([[ENIAC]])
|[[Mainframe]] computer ([[IBM System/360]])
|[[Smartphone]] ([[LYF]] Water 2)
|[[Desktop computer]] (IBM [[ThinkCentre#S50|ThinkCentre S50]] with monitor)
|[[Video game console]] (Nintendo [[GameCube]])
|[[Supercomputer]] (IBM [[Summit (supercomputer)|Summit]])
}}
}}

A '''computer''' is a [[machine]] that can be [[Computer programming|programmed]] to automatically [[Execution (computing)|carry out]] sequences of [[arithmetic]] or [[logical operations]] (''[[computation]]''). Modern [[digital electronic]] computers can perform generic sets of operations known as [[Computer program|''programs'']], which enable computers to perform a wide range of tasks. The term '''computer system''' may refer to a nominally complete computer that includes the [[Computer hardware|hardware]], [[operating system]], [[software]], and [[peripheral]] equipment needed and used for full operation; or to a group of computers that are linked and function together, such as a [[computer network]] or [[computer cluster]].

A broad range of [[Programmable logic controller|industrial]] and [[Consumer electronics|consumer products]] use computers as [[control system]]s, including simple special-purpose devices like [[microwave oven]]s and [[remote control]]s, and factory devices like [[industrial robot]]s. Computers are at the core of general-purpose devices such as [[personal computer]]s and [[mobile device]]s such as [[smartphone]]s. Computers power the [[Internet]], which links billions of computers and users.

Early computers were meant to be used only for [[calculations]]. Simple manual instruments like the [[abacus]] have aided people in doing calculations since ancient times. Early in the [[Industrial Revolution]], some mechanical devices were built to automate long, tedious tasks, such as guiding patterns for [[loom]]s. More sophisticated electrical machines did specialized [[Analogue electronics|analog]] calculations in the early 20th century. The first [[Digital data|digital]] electronic calculating machines were developed during [[World War II]], both [[Mechanical computer|electromechanical]] and using [[thermionic valve]]s. The first [[semiconductor]] [[transistor]]s in the late 1940s were followed by the [[silicon]]-based [[MOSFET]] (MOS transistor) and [[monolithic integrated circuit]] chip technologies in the late 1950s, leading to the [[microprocessor]] and the [[microcomputer revolution]] in the 1970s. The speed, power, and versatility of computers have been increasing dramatically ever since then, with [[transistor count]]s increasing at a rapid pace ([[Moore's law]] noted that counts doubled every two years), leading to the [[Digital Revolution]] during the late 20th and early 21st centuries.

Conventionally, a modern computer consists of at least one [[processing element]], typically a [[central processing unit]] (CPU) in the form of a [[microprocessor]], together with some type of [[computer memory]], typically [[semiconductor memory]] chips. The processing element carries out arithmetic and logical operations, and a sequencing and control unit can change the order of operations in response to stored [[data|information]]. Peripheral devices include input devices ([[Keyboard technology|keyboards]], [[Computer mouse|mice]], [[joysticks]], etc.), output devices ([[Computer monitor|monitors]], [[Printer (computing)|printers]], etc.), and [[Input and output devices|input/output devices]] that perform both functions (e.g. [[touchscreen|touchscreens]]). Peripheral devices allow information to be retrieved from an external source, and they enable the results of operations to be saved and retrieved.
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== Etymology ==
[[File:X-4 with Female Computer - GPN-2000-001932.jpg|thumb|upright=1.15|A [[human computer]], with microscope and calculator, 1952|alt=A human computer.]]
It was not until the mid-20th century that the word acquired its modern definition; according to the ''[[Oxford English Dictionary]]'', the first known use of the word ''computer'' was in a different sense, in a 1613 book called ''The Yong Mans Gleanings'' by the English writer [[Richard Brathwait]]: "I haue {{sic}} read the truest computer of Times, and the best Arithmetician that euer {{sic|nolink=y}} breathed, and he reduceth thy dayes into a short number." This usage of the term referred to a [[human computer]], a person who carried out calculations or [[computation]]s. The word continued to have 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.{{Sfn|Evans|2018|p=23}} By 1943, most human computers were women.{{Sfn|Smith|2013|p=6}}

The ''[[Online Etymology Dictionary]]'' gives the first attested use of ''computer'' in the 1640s, meaning 'one who calculates'; this is an "agent noun from compute (v.)". The ''Online Etymology Dictionary'' states that the use of the term to mean {{" '}}calculating machine' (of any type) is from 1897." The ''Online Etymology Dictionary'' indicates that the "modern use" of the term, to mean 'programmable digital electronic computer' dates from "1945 under this name; [in a] theoretical [sense] from 1937, as ''[[Turing machine]]''".<ref>{{cite web |title=computer (n.) |url=http://www.etymonline.com/index.php?term=computer |url-status=live |access-date=2021-08-19 |website=Online Etymology Dictionary |language=en-US |archive-date=16 November 2016 |archive-url=https://web.archive.org/web/20161116065135/http://www.etymonline.com/index.php?term=computer }}</ref> The name has remained, although modern computers are capable of many higher-level functions.

== History ==
{{Main|History of computing|History of computing hardware}}
{{For timeline|Timeline of computing}}

=== Pre-20th century ===
[[File:Os d'Ishango IRSNB.JPG|thumb|upright=0.65|The [[Ishango bone]], a [[bone tool]] dating back to [[prehistoric Africa]]]]
Devices have been used to aid computation for thousands of years, mostly using [[one-to-one correspondence]] with [[finger counting|fingers]]. The earliest counting device was most likely a form of [[tally stick]]. Later record keeping aids throughout the [[Fertile Crescent]] included calculi (clay spheres, cones, etc.) which represented counts of items, likely livestock or grains, sealed in hollow unbaked clay containers.{{efn|According to {{harvnb|Schmandt-Besserat|1981}}, these clay containers contained tokens, the total of which were the count of objects being transferred. The containers thus served as something of a [[bill of lading]] or an accounts book. In order to avoid breaking open the containers, first, clay impressions of the tokens were placed on the outside of the containers, for the count; the shapes of the impressions were abstracted into stylized marks; finally, the abstract marks were systematically used as numerals; these numerals were finally formalized as numbers.<br />Eventually the marks on the outside of the containers were all that were needed to convey the count, and the clay containers evolved into clay tablets with marks for the count. {{harvnb|Schmandt-Besserat|1999}} estimates it took 4000 years.}}<ref>{{Cite book|first=Eleanor|last=Robson|author-link=Eleanor Robson|year=2008 |title=Mathematics in Ancient Iraq|isbn=978-0-691-09182-2|page=5|publisher=Princeton University Press }}: calculi were in use in Iraq for primitive accounting systems as early as 3200–3000 BCE, with commodity-specific counting representation systems. Balanced accounting was in use by 3000–2350 BCE, and a [[sexagesimal number system]] was in use 2350–2000 BCE.</ref> The use of [[counting rods]] is one example.

[[File:Abacus 6.png|thumb|upright=1.15|left|The Chinese [[suanpan]] ({{lang|zh|算盘}}). The number represented on this [[abacus]] is 6,302,715,408.]]
The [[abacus]] was initially used for arithmetic tasks. The [[Roman abacus]] was developed from devices used in [[Babylonia]] as early as 2400 BCE. Since then, many other forms of reckoning boards or tables have been invented. In a medieval European [[counting house]], a checkered cloth would be placed on a table, and markers moved around on it according to certain rules, as an aid to calculating sums of money.<ref>{{Cite book |author=Flegg, Graham. |title=Numbers through the ages |date=1989 |publisher=Macmillan Education|isbn=0-333-49130-0|location=Houndmills, Basingstoke, Hampshire |language=en-US |oclc=24660570}}</ref>

[[File:Antikythera Fragment A (Front).webp|thumb|upright=0.8|The [[Antikythera mechanism]], dating back to [[ancient Greece]] circa 200–80 BCE, is an early [[analog computing]] device.]]
The [[Antikythera mechanism]] is believed to be the earliest known mechanical [[analog computer]], according to [[Derek J. de Solla Price]].<ref>[http://www.antikythera-mechanism.gr/project/general/the-project.html ''The Antikythera Mechanism Research Project''] {{Webarchive|url=https://web.archive.org/web/20080428070448/http://www.antikythera-mechanism.gr/project/general/the-project.html |date=28 April 2008 }}, The Antikythera Mechanism Research Project. Retrieved 1 July 2007.</ref> It was designed to calculate astronomical positions. It was discovered in 1901 in the [[Antikythera wreck]] off the Greek island of [[Antikythera]], between [[Kythera]] and [[Crete]], and has been dated to approximately {{circa|100 BCE}}. Devices of comparable complexity to the Antikythera mechanism would not reappear until the fourteenth century.<ref>{{Cite journal |last=Marchant |first=Jo |date=1 November 2006 |title=In search of lost time |journal=Nature |volume=444 |issue=7119 |pages=534–538 |doi=10.1038/444534a |pmid=17136067 |bibcode=2006Natur.444..534M |s2cid=4305761 |doi-access=free  | issn = 0028-0836}}</ref>

Many mechanical aids to calculation and measurement were constructed for astronomical and navigation use. The [[planisphere]] was a [[star chart]] invented by [[Al-Biruni|Abū Rayhān al-Bīrūnī]] in the early 11th century.<ref name="Wiet">G. Wiet, V. Elisseeff, P. Wolff, J. Naudu (1975). ''History of Mankind, Vol 3: The Great medieval Civilisations'', p. 649. George Allen & Unwin Limited, [[UNESCO]].</ref> The [[astrolabe]] was invented in the [[Hellenistic civilization|Hellenistic world]] in either the 1st or 2nd centuries BCE and is often attributed to [[Hipparchus]]. A combination of the [[planisphere]] and [[dioptra]], the astrolabe was effectively an analog computer capable of working out several different kinds of problems in [[spherical astronomy]]. An astrolabe incorporating a mechanical [[calendar]] computer<ref>Fuat Sezgin. "Catalogue of the Exhibition of the Institute for the History of Arabic-Islamic Science (at the Johann Wolfgang Goethe University", Frankfurt, Germany), Frankfurt Book Fair 2004, pp.&nbsp;35 & 38.</ref><ref>{{cite journal |first=François |last=Charette |title=Archaeology: High tech from Ancient Greece |journal=Nature |volume=444 |issue=7119 |pages=551–552 |year=2006 |doi=10.1038/444551a|pmid=17136077 |bibcode=2006Natur.444..551C |s2cid=33513516 |doi-access=free }}</ref> and [[gear]]-wheels was invented by Abi Bakr of [[Isfahan]], [[Persia]] in 1235.<ref>{{cite journal|first1=Silvio A.|last1=Bedini|first2=Francis R.|last2=Maddison|year=1966|title=Mechanical Universe: The Astrarium of Giovanni de' Dondi|journal=Transactions of the American Philosophical Society|volume=56|issue=5|pages=1–69|jstor=1006002|doi=10.2307/1006002}}</ref> Abū Rayhān al-Bīrūnī invented the first mechanical geared [[lunisolar calendar]] astrolabe,<ref>{{cite journal|first=Derek de S.|last=Price|author-link=Derek J. de Solla Price|year=1984|title=A History of Calculating Machines|journal=IEEE Micro|volume=4|number=1|pages=22–52|doi=10.1109/MM.1984.291305}}</ref> an early fixed-[[wire]]d knowledge processing machine<ref name=Oren>{{cite journal|first=Tuncer|last=Őren|author-link=Tuncer Őren|year=2001|title=Advances in Computer and Information Sciences: From Abacus to Holonic Agents|url=http://www.site.uottawa.ca/~oren/pubs/pubs-2001-02-Tubitak.pdf|journal=Turk J Elec Engin|volume=9|number=1|pages=63–70|access-date=21 April 2016|archive-date=15 September 2009|archive-url=https://web.archive.org/web/20090915033859/http://www.site.uottawa.ca/~oren/pubs/pubs-2001-02-Tubitak.pdf|url-status=live}}</ref> with a [[gear train]] and gear-wheels,<ref>[[Donald Routledge Hill]] (1985). "Al-Biruni's mechanical calendar", ''Annals of Science'' '''42''', pp.&nbsp;139–163.</ref> {{circa|1000 AD}}.

The [[Sector (instrument)|sector]], a calculating instrument used for solving problems in proportion, [[trigonometry]], multiplication and division, and for various functions, such as squares and cube roots, was developed in the late 16th century and found application in gunnery, surveying and navigation.

The [[planimeter]] was a manual instrument to calculate the area of a closed figure by tracing over it with a mechanical linkage.

[[File:Sliderule 2005.png|thumb|upright=1.25|left|A [[slide rule]]]]
The [[slide rule]] was invented around 1620–1630, by the English clergyman [[William Oughtred]], shortly after the publication of the concept of the [[logarithm]]. It is a hand-operated analog computer for doing multiplication and division. As slide rule development progressed, added scales provided reciprocals, squares and square roots, cubes and cube roots, as well as [[transcendental function]]s such as logarithms and exponentials, circular and [[hyperbolic functions|hyperbolic]] trigonometry and other [[Function (mathematics)|functions]]. Slide rules with special scales are still used for quick performance of routine calculations, such as the [[E6B]] circular slide rule used for time and distance calculations on light aircraft.

In the 1770s, [[Pierre Jaquet-Droz]], a Swiss [[watchmaker]], built a mechanical doll ([[automata|automaton]]) that could write holding a quill pen. By switching the number and order of its internal wheels different letters, and hence different messages, could be produced. In effect, it could be mechanically "programmed" to read instructions. Along with two other complex machines, the doll is at the Musée d'Art et d'Histoire of [[Neuchâtel]], [[Switzerland]], and still operates.<ref>{{cite web |date=11 July 2013 |title=The Writer Automaton, Switzerland |url=http://www.chonday.com/Videos/the-writer-automaton  |publisher=chonday.com |access-date=28 January 2015 |archive-date=20 February 2015 |archive-url=https://web.archive.org/web/20150220154407/http://www.chonday.com/Videos/the-writer-automaton }}</ref>

In 1831–1835, mathematician and engineer [[Giovanni Plana]] devised a [[Cappella dei Mercanti (Turin)#Perpetual calendar|Perpetual Calendar machine]], which through a system of pulleys and cylinders could predict the [[perpetual calendar]] for every year from 0 CE (that is, 1 BCE) to 4000 CE, keeping track of leap years and varying day length. The [[tide-predicting machine]] invented by the Scottish scientist [[William Thomson, 1st Baron Kelvin|Sir William Thomson]] in 1872 was of great utility to navigation in shallow waters. It used a system of pulleys and wires to automatically calculate predicted tide levels for a set period at a particular location.

The [[differential analyser]], a mechanical analog computer designed to solve [[differential equation]]s by [[integral|integration]], used wheel-and-disc mechanisms to perform the integration. In 1876, Sir William Thomson had already discussed the possible construction of such calculators, but he had been stymied by the limited output torque of the [[ball-and-disk integrator]]s.<ref name="scientific-computing.com">Ray Girvan, [http://www.scientific-computing.com/scwmayjun03computingmachines.html "The revealed grace of the mechanism: computing after Babbage"], {{webarchive|url=https://web.archive.org/web/20121103094710/http://www.scientific-computing.com/scwmayjun03computingmachines.html|date=3 November 2012}}, ''Scientific Computing World'', May/June 2003.</ref> In a differential analyzer, the output of one integrator drove the input of the next integrator, or a graphing output. The [[torque amplifier]] was the advance that allowed these machines to work. Starting in the 1920s, [[Vannevar Bush]] and others developed mechanical differential analyzers.

In the 1890s, the Spanish engineer [[Leonardo Torres Quevedo]] began to develop a series of advanced [[Leonardo Torres Quevedo#Analogue calculating machines|analog machines]] that could solve real and complex roots of [[polynomial]]s,<ref>{{Cite journal |last=Torres |first=Leonardo |author-link=Leonardo Torres Quevedo |date=1895-10-10 |title=Memória sobre las Máquinas Algébricas |url=https://quickclick.es/rop/pdf/publico/1895/1895_tomoI_28_01.pdf |journal=Revista de Obras Públicas |language=es |issue=28 |pages=217–222}}</ref><ref name="MaquinasAlgebricasLTQ">Leonardo Torres. ''[https://books.google.com/books?id=Eo0NAQAAIAAJ Memoria sobre las máquinas algébricas: con un informe de la Real academia de ciencias exactas, fisicas y naturales]'', Misericordia, 1895.</ref><ref name="Thomas2008">{{Cite journal |last=Thomas |first=Federico |date=2008-08-01 |title=A short account on Leonardo Torres' endless spindle |url=https://www.sciencedirect.com/science/article/pii/S0094114X07001231 |journal=[[Mechanism and Machine Theory]] |publisher=[[International Federation for the Promotion of Mechanism and Machine Science|IFToMM]] |volume=43 |issue=8 |pages=1055–1063 |doi=10.1016/j.mechmachtheory.2007.07.003 |issn=0094-114X|hdl=10261/30460 |hdl-access=free }}</ref><ref name="Gomez-JaureguiGutierrez-GarciaGonzález-RedondoIglesiasManchadoOtero2022">{{Cite journal |last1=Gomez-Jauregui |first1=Valentin |last2=Gutierrez-Garcia |first2=Andres |last3=González-Redondo |first3=Francisco A. |last4=Iglesias |first4=Miguel |last5=Manchado |first5=Cristina |last6=Otero |first6=Cesar |date=2022-06-01 |title=Torres Quevedo's mechanical calculator for second-degree equations with complex coefficients|journal=[[Mechanism and Machine Theory]] |publisher=[[International Federation for the Promotion of Mechanism and Machine Science|IFToMM]] |volume=172 |issue=8|page=104830 |doi=10.1016/j.mechmachtheory.2022.104830|s2cid=247503677 |doi-access=free |hdl=10902/24391 |hdl-access=free }}</ref> which were published in 1901 by the [[French Academy of Sciences|Paris Academy of Sciences]].<ref>{{cite journal|date=1901|first=Leonardo|language=fr|last=Torres Quevedo|publisher=Impr. nationale (París)|title=Machines á calculer|url=https://gallica.bnf.fr/ark:/12148/bpt6k840139b?rk=21459;2 |journal=Mémoires Présentés par Divers Savants à l'Académie des Scienes de l'Institut de France |volume=XXXII}}<!-- auto-translated by Module:CS1 translator --></ref>

=== First computer ===
[[File:Charles Babbage - 1860.jpg|thumb|left|upright=0.8|[[Charles Babbage]]]]
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|caption1 = A diagram of a portion of Babbage's [[Difference engine]]
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|caption2 = The Difference Engine Number 2 at the [[Intellectual Ventures]] laboratory in Seattle
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[[Charles Babbage]], an English mechanical engineer and [[polymath]], originated the concept of a programmable computer. Considered the "[[computer pioneer|father of the computer]]",<ref>{{cite book |author=Halacy, Daniel Stephen |title=Charles Babbage, Father of the Computer |url=https://archive.org/details/charlesbabbagefa00hala |url-access=registration |year=1970 |publisher=Crowell-Collier Press |isbn=978-0-02-741370-0 }}</ref> he conceptualized and invented the first [[mechanical computer]] in the early 19th century.

After working on his [[difference engine]] he announced his invention in 1822, in a paper to the [[Royal Astronomical Society]], titled "Note on the application of machinery to the computation of astronomical and mathematical tables".<ref>{{cite web |last1=O'Connor |first1=John J. |last2=Robertson |first2=Edmund F. |author-link2=Edmund F. Robertson |date=1998 |url=http://www-gap.dcs.st-and.ac.uk/~history/Mathematicians/Babbage.html |title=Charles Babbage |work=MacTutor History of Mathematics archive |publisher=School of Mathematics and Statistics, University of St Andrews, Scotland |access-date=2006-06-14 |archive-url=https://web.archive.org/web/20060616002258/http://www-gap.dcs.st-and.ac.uk/~history/Mathematicians/Babbage.html |archive-date=2006-06-16 }}</ref> He also designed to aid in navigational calculations, in 1833 he realized that a much more general design, an [[analytical engine]], was possible. The input of programs and data was to be provided to the machine via [[punched card]]s, a method being used at the time to direct mechanical [[loom]]s such as the [[Jacquard loom]]. For output, the machine would have a [[Printer (computing)|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 would incorporate an [[arithmetic logic unit]], [[control flow]] in the form of [[conditional branching]] and [[program loop#Loops|loops]], and integrated [[computer memory|memory]], making it the first design for a general-purpose computer that could be described in modern terms as [[Turing-complete]].<ref name="babbageonline">{{cite web |date=19 January 2007 |title=Babbage |url=http://www.sciencemuseum.org.uk/onlinestuff/stories/babbage.aspx?page=5  |access-date=1 August 2012 |work=Online stuff |publisher=Science Museum |archive-date=7 August 2012 |archive-url=https://web.archive.org/web/20120807185334/http://www.sciencemuseum.org.uk/onlinestuff/stories/babbage.aspx?page=5 }}</ref><ref>{{cite web |last=Graham-Cumming |first=John |date=23 December 2010 |title=Let's build Babbage's ultimate mechanical computer |url=https://www.newscientist.com/article/mg20827915.500-lets-build-babbages-ultimate-mechanical-computer.html |url-status=live |access-date=1 August 2012 |work=opinion |publisher=New Scientist |language=en-US |archive-date=5 August 2012 |archive-url=https://web.archive.org/web/20120805050111/http://www.newscientist.com/article/mg20827915.500-lets-build-babbages-ultimate-mechanical-computer.html }}</ref>

The machine was about a century ahead of its time. All the parts for his machine had to be made by hand – this was a major problem for a device with thousands of parts. Eventually, the project was dissolved with the decision of the [[British Government]] to cease funding. Babbage's failure to complete the analytical engine can be chiefly attributed to political and financial difficulties as well as his desire to develop an increasingly sophisticated computer and to move ahead faster than anyone else could follow. Nevertheless, his son, [[Henry Babbage]], completed a simplified version of the analytical engine's computing unit (the ''mill'') in 1888. He gave a successful demonstration of its use in computing tables in 1906.

=== Electromechanical calculating machine ===
[[File:Aritmómetro_Electromecánico.jpg|thumb|left|Electro-mechanical calculator (1920) by [[Leonardo Torres Quevedo]].]]

In his work ''Essays on Automatics'' published in 1914, [[Leonardo Torres Quevedo]] wrote a brief history of Babbage's efforts at constructing a mechanical Difference Engine and Analytical Engine. The paper contains a design of a machine capable to calculate formulas like <math>a^x(y - z)^2</math>, for a sequence of sets of values. The whole machine was to be controlled by a [[Read-only memory|read-only]] program, which was complete with provisions for [[conditional branching]]. He also introduced the idea of [[floating-point arithmetic]].<ref name="LTQ1914es">L. Torres Quevedo. ''Ensayos sobre Automática – Su definicion. Extension teórica de sus aplicaciones,'' Revista de la Academia de Ciencias Exacta, Revista 12, pp. 391–418, 1914.</ref><ref>Torres Quevedo, Leonardo. [https://quickclick.es/rop/pdf/publico/1914/1914_tomoI_2043_01.pdf Automática: Complemento de la Teoría de las Máquinas, (pdf)], pp. 575–583, Revista de Obras Públicas, 19 November 1914.</ref><ref>Ronald T. Kneusel. ''[https://books.google.com/books?id=eq4ZDgAAQBAJ&dq=leonardo+torres+quevedo++electromechanical+machine+essays&pg=PA84 Numbers and Computers],'' Springer, pp. 84–85, 2017. {{ISBN|978-3-319-50508-4}}</ref> In 1920, to celebrate the 100th anniversary of the invention of the [[arithmometer]], Torres presented in Paris the Electromechanical Arithmometer, which allowed a user to input arithmetic problems through a [[Keyboard layout|keyboard]], and computed and printed the results,{{Sfn|Randell|1982|p=6, 11–13}}<ref name="Randell1982p109">B. Randell. ''Electromechanical Calculating Machine,'' The Origins of Digital Computers, pp.109–120, 1982.</ref>{{sfn|Bromley|1990}}<ref>Cristopher Moore, Stephan Mertens. ''[https://books.google.com/books?id=z4zMiZyAE1kC&dq=leonardo+torres+quevedo+++computing&pg=PA291 The Nature of Computation],'' Oxford, England: Oxford University Press, p. 291, 2011. {{ISBN|978-0-199-23321-2}}.</ref> demonstrating the feasibility of an electromechanical analytical engine.<ref>Randell, Brian. [https://dl.acm.org/doi/pdf/10.5555/1074100.1074334 Digital Computers, History of Origins, (pdf)], p. 545, Digital Computers: Origins, Encyclopedia of Computer Science, January 2003.</ref>

=== Analog computers ===
{{Main|Analog computer}}
[[File:099-tpm3-sk.jpg|thumb|left|upright=0.9|[[William Thomson, 1st Baron Kelvin|Sir William Thomson]]'s third tide-predicting machine design, 1879–81]]
During the first half of the 20th century, many scientific [[computing]] needs were met by increasingly sophisticated analog computers, which used a direct mechanical or electrical model of the problem as a basis for [[computation]]. However, these were not programmable and generally lacked the versatility and accuracy of modern digital computers.<ref name="stanf">{{cite book |url=http://plato.stanford.edu/entries/computing-history/ |title=The Modern History of Computing |publisher=Stanford Encyclopedia of Philosophy |year=2017 |language=en-US |access-date=7 January 2014 |archive-date=12 July 2010 |archive-url=https://web.archive.org/web/20100712072148/http://plato.stanford.edu/entries/computing-history/ |url-status=live }}</ref> The first modern analog computer was a [[tide-predicting machine]], invented by [[William Thomson, 1st Baron Kelvin|Sir William Thomson]] (later to become Lord Kelvin) in 1872. The [[differential analyser]], a mechanical analog computer designed to solve differential equations by integration using wheel-and-disc mechanisms, was conceptualized in 1876 by [[James Thomson (engineer)|James Thomson]], the elder brother of the more famous Sir William Thomson.<ref name="scientific-computing.com" />

The art of mechanical analog computing reached its zenith with the [[differential analyzer]], completed in 1931 by [[Vannevar Bush]] at [[Massachusetts Institute of Technology|MIT]].<ref>{{Cite web |date=2000-05-01 |title=Computing Before Silicon |url=https://www.technologyreview.com/2000/05/01/236348/computing-before-silicon/ |access-date=2025-05-18 |website=MIT Technology Review |language=en}}</ref> By the 1950s, the success of digital electronic computers had spelled the end for most analog computing machines, but analog computers remained in use during the 1950s in some specialized applications such as education ([[slide rule]]) and aircraft ([[control system]]s).{{Citation needed|date=February 2025}}

=== Digital computers ===

==== Electromechanical ====
[[Claude Shannon]]'s 1937 [[A Symbolic Analysis of Relay and Switching Circuits|master's thesis]] laid the foundations of digital computing, with his insight of applying Boolean algebra to the analysis and synthesis of switching circuits being the basic concept which underlies all electronic digital computers.<ref>{{Cite book |url=https://books.google.com/books?id=081H96F1enMC |title=A Brief History of Computing |date=2008 |publisher=Springer London |isbn=978-1-84800-083-4 |editor-last=O’Regan |editor-first=Gerard |location=London |pages=28 |language=en |doi=10.1007/978-1-84800-084-1}}</ref><ref name=":1">{{Cite web |last=Tse |first=David |author-link=David Tse |date=2020-12-22 |title=How Claude Shannon Invented the Future |url=https://www.quantamagazine.org/how-claude-shannons-information-theory-invented-the-future-20201222/ |access-date=2024-11-05 |website=Quanta Magazine}}</ref>

By 1938, the [[United States Navy]] had developed the [[Torpedo Data Computer]], an electromechanical analog computer for [[submarine|submarines]] that used trigonometry to solve the problem of firing a torpedo at a moving target. During [[World War II]], similar devices were developed in other countries.<ref>{{Cite web |last=Parmar |first=Sunil |date=2021-09-23 |title=Restoration of the TDC MARK III aboard USS PAMPANITO |url=https://archive.navalsubleague.org/1995/restoration-of-the-tdc-mark-m-aboard-pampanito |access-date=2025-05-17 |website=NSL Archive |language=en-US}}</ref>

[[File:Z3 Deutsches Museum.JPG|thumb|left|upright=0.9|Replica of [[Konrad Zuse]]'s [[Z3 (computer)|Z3]], the first fully automatic, digital (electromechanical) computer]]
Early digital computers were [[electromechanics|electromechanical]]; electric switches drove mechanical relays to perform the calculation. These devices had a low operating speed and were eventually superseded by much faster all-electric computers, originally using [[vacuum tube]]s. The [[Z2 (computer)|Z2]], created by German engineer [[Konrad Zuse]] in 1939 in [[Berlin]], was one of the earliest examples of an electromechanical relay computer.<ref name="Part 4 Zuse">{{cite web|url=http://www.epemag.com/zuse/part4a.htm|title=Part 4: Konrad Zuse's Z1 and Z3 Computers|last=Zuse|first=Horst|work=The Life and Work of Konrad Zuse|publisher=EPE Online|access-date=17 June 2008 |archive-url=https://web.archive.org/web/20080601210541/http://www.epemag.com/zuse/part4a.htm |archive-date=1 June 2008}}</ref>

[[File:Konrad Zuse (1992).jpg|thumb|right|upright=0.6|[[Konrad Zuse]], inventor of the modern computer<ref name="Bellis">{{cite web |last=Bellis |first=Mary |date=15 May 2019 |orig-date=First published 2006 at inventors.about.com/library/weekly/aa050298.htm |title=Biography of Konrad Zuse, Inventor and Programmer of Early Computers |url=https://www.thoughtco.com/konrad-zuse-modern-computer-4078237 |url-status=live |archive-url=https://web.archive.org/web/20201213003237/https://www.thoughtco.com/konrad-zuse-modern-computer-4078237 |archive-date=13 December 2020 |access-date=3 February 2021 |website=thoughtco.com |publisher=Dotdash Meredith |quote=Konrad Zuse earned the semiofficial title of 'inventor of the modern computer'{{who|date=February 2023}}.}}</ref><ref>{{Cite web|url=https://www.computerhope.com/issues/ch001335.htm|title=Who is the Father of the Computer?|website=ComputerHope}}</ref>]]
In 1941, Zuse followed his earlier machine up with the [[Z3 (computer)|Z3]], the world's first working electromechanical [[Computer programming|programmable]], fully automatic digital computer.<ref>{{Cite book|last=Zuse|first=Konrad|author-link=Konrad Zuse|title=The Computer – My Life ''Translated by McKenna, Patricia and Ross, J. Andrew from:'' Der Computer, mein Lebenswerk (1984)|place=Berlin/Heidelberg|publisher=Springer-Verlag|orig-date=1984|year=2010|language=en|isbn=978-3-642-08151-4}}</ref><ref>{{cite news |last=Salz Trautman |first=Peggy |date=20 April 1994 |title=A Computer Pioneer Rediscovered, 50 Years On |newspaper=[[The New York Times]] |url=https://www.nytimes.com/1994/04/20/news/20iht-zuse.html  |access-date=15 February 2017 |archive-date=4 November 2016 |archive-url=https://web.archive.org/web/20161104051054/http://www.nytimes.com/1994/04/20/news/20iht-zuse.html }}</ref> The Z3 was built with 2000 [[relay]]s, implementing a 22 [[bit]] [[Word (computer architecture)|word length]] that operated at a [[clock frequency]] of about 5–10 [[Hertz|Hz]].<ref>{{cite book|last=Zuse|first=Konrad|author-link=Konrad Zuse|title=Der Computer. Mein Lebenswerk.|edition=3rd|year=1993|publisher=Springer-Verlag|location=Berlin|language=de|isbn=978-3-540-56292-4|page=55}}</ref> Program code was supplied on punched [[celluloid|film]] while data could be stored in 64 words of memory or supplied from the keyboard. It was quite similar to modern machines in some respects, pioneering numerous advances such as [[floating-point number]]s. Rather than the harder-to-implement decimal system (used in [[Charles Babbage]]'s earlier design), using a [[binary number|binary]] system meant that Zuse's machines were easier to build and potentially more reliable, given the technologies available at that time.<ref>{{cite web|url=https://goremotesupport.com/blog/crash-the-story-of-it-zuse|title=Crash! The Story of IT: Zuse|access-date=1 June 2016|url-status=usurped|archive-url=https://web.archive.org/web/20160918203643/https://goremotesupport.com/blog/crash-the-story-of-it-zuse/|archive-date=18 September 2016}}</ref> The Z3 was not itself a universal computer but could be extended to be [[Turing complete]].<ref name="rojas-ieee">{{cite journal|last=Rojas |first=R. |s2cid=14606587 |title=How to make Zuse's Z3 a universal computer |journal=IEEE Annals of the History of Computing |volume=20 |issue=3 |pages=51–54 |year=1998 |doi=10.1109/85.707574 |author-link=Raúl Rojas}}</ref><ref name="rojas-universal">{{cite web |last=Rojas |first=Raúl |title=How to Make Zuse's Z3 a Universal Computer |url=http://www.inf.fu-berlin.de/users/rojas/1997/Universal_Computer.pdf |url-status=live |access-date=2015-09-28 |website=fu-berlin.de |archive-date=9 August 2017 |archive-url=https://web.archive.org/web/20170809123935/http://www.inf.fu-berlin.de/users/rojas/1997/Universal_Computer.pdf }}</ref>

Zuse's next computer, the [[Z4 (computer)|Z4]], became the world's first commercial computer; after initial delay due to the Second World War, it was completed in 1950 and delivered to the [[ETH Zurich]].<ref name="OReganZuse">{{Cite book |last=O'Regan |first=Gerard |title=A Brief History of Computing |publisher=Springer Nature |year=2010 |isbn=978-3-030-66599-9 |page=65 |language=en-US}}</ref> The computer was manufactured by Zuse's own company, [[Zuse KG]], which was founded in 1941 as the first company with the sole purpose of developing computers in Berlin.<ref name="OReganZuse" /> The Z4 served as the inspiration for the construction of the [[ERMETH]], the first Swiss computer and one of the first in Europe.<ref>{{Cite book |last=Bruderer |first=Herbert |title=Milestones in Analog and Digital Computing |publisher=Springer |year=2021 |isbn=978-3-03040973-9 |edition=3rd |pages=1009, 1087}}</ref>

==== Vacuum tubes and digital electronic circuits ====
{{Anchor|Digital computer|Digital}}
Purely [[electronic circuit]] elements soon replaced their mechanical and electromechanical equivalents, at the same time that digital calculation replaced analog. The engineer [[Tommy Flowers]], working at the [[Post Office Research Station]] in London in the 1930s, began to explore the possible use of electronics for the [[telephone exchange]]. Experimental equipment that he built in 1934 went into operation five years later, converting a portion of the [[telephone exchange]] network into an electronic data processing system, using thousands of [[vacuum tube]]s.<ref name="stanf" /> In the US, [[John Vincent Atanasoff]] and [[Clifford Berry|Clifford E. Berry]] of [[Iowa State University]] developed and tested the [[Atanasoff–Berry Computer]] (ABC) in 1942,<ref>{{cite news |date=15 January 1941 |title=notice |work=Des Moines Register}}</ref> the first "automatic electronic digital computer".<ref>{{cite book|title=The First Electronic Computer|author=Arthur W. Burks|year=1989|publisher=University of Michigan Press |url={{GBurl|id=_Zja6hoP4psC}}|isbn=0-472-08104-7|access-date=1 June 2019}}</ref> This design was also all-electronic and used about 300 vacuum tubes, with capacitors fixed in a mechanically rotating drum for memory.<ref name=Copeland2006>{{Cite book|last=Copeland|first=Jack|year=2006|title=Colossus: The Secrets of Bletchley Park's Codebreaking Computers|location=Oxford|publisher=[[Oxford University Press]]|pages=101–115|isbn=978-0-19-284055-4}}</ref>

[[File:Colossus.jpg|thumb|upright=1.15|[[Colossus computer|Colossus]], the first [[Digital electronics|electronic digital]] programmable computing device, was used to break German ciphers during World War II. It is seen here in use at [[Bletchley Park]] in 1943.|alt=Two women are seen by the Colossus computer.]]
During World War II, the British code-breakers at [[Bletchley Park]] achieved a number of successes at breaking encrypted German military communications. The German encryption machine, [[Enigma machine|Enigma]], was first attacked with the help of the electro-mechanical [[bombe]]s which were often run by women.<ref name=":0">{{Cite news |last=Miller |first=Joe |date=November 10, 2014 |title=The woman who cracked Enigma cyphers |language=en-GB |work=BBC News |url=https://www.bbc.com/news/technology-29840653 |url-status=live |access-date=October 14, 2018 |archive-date=10 November 2014 |archive-url=https://web.archive.org/web/20141110140239/https://www.bbc.com/news/technology-29840653 }}</ref><ref>{{Cite news |last=Bearne |first=Suzanne |date=July 24, 2018 |title=Meet the female codebreakers of Bletchley Park |url=https://www.theguardian.com/careers/2018/jul/24/meet-the-female-codebreakers-of-bletchley-park |url-status=live |access-date=October 14, 2018 |website=The Guardian |language=en |archive-date=7 February 2019 |archive-url=https://web.archive.org/web/20190207020226/https://www.theguardian.com/careers/2018/jul/24/meet-the-female-codebreakers-of-bletchley-park }}</ref> To crack the more sophisticated German [[Lorenz SZ 40/42]] machine, used for high-level Army communications, [[Max Newman]] and his colleagues commissioned Flowers to build the [[Colossus computer|Colossus]].<ref name=Copeland2006 /> He spent eleven months from early February 1943 designing and building the first Colossus.<ref>{{Cite news |title=Bletchley's code-cracking Colossus |language=en-US |work=BBC |url=http://news.bbc.co.uk/2/hi/technology/8492762.stm |access-date=2021-11-24 |archive-date=4 February 2010 |archive-url=https://web.archive.org/web/20100204035124/http://news.bbc.co.uk/2/hi/technology/8492762.stm |url-status=live }}</ref> After a functional test in December 1943, Colossus was shipped to Bletchley Park, where it was delivered on 18 January 1944<ref name="The Colossus Computer">{{cite web|url=http://www.tnmoc.org/colossus-rebuild-story|title=Colossus – The Rebuild Story|website=The National Museum of Computing|access-date=7 January 2014|archive-url=https://web.archive.org/web/20150418230306/http://www.tnmoc.org/colossus-rebuild-story|archive-date=18 April 2015}}</ref> and attacked its first message on 5 February.<ref name="Copeland2006" />

Colossus was the world's first [[Digital electronics|electronic digital]] programmable computer.<ref name="stanf" /> 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]]al operations on its data, but it was not Turing-complete. Nine Mk II Colossi were built (The Mk I was converted to a Mk II making ten machines in total). Colossus Mark I contained 1,500 thermionic valves (tubes), but Mark II with 2,400 valves, was both five times faster and simpler to operate than Mark I, greatly speeding the decoding process.<ref>{{Cite news |last1=Randell|first1=Brian|author-link1=Brian Randell|last2=Fensom|first2=Harry|last3=Milne|first3=Frank A.|title=Obituary: Allen Coombs|newspaper=The Independent|date=15 March 1995|url=https://www.independent.co.uk/news/people/obituary-allen-coombs-1611270.html|access-date=18 October 2012|archive-date=3 February 2012|archive-url=https://web.archive.org/web/20120203042657/http://www.independent.co.uk/news/people/obituary-allen-coombs-1611270.html|url-status=live}}</ref><ref>{{Cite news |last=Fensom|first=Jim|title=Harry Fensom obituary|date=8 November 2010|url=https://www.theguardian.com/theguardian/2010/nov/08/harry-fensom-obituary|access-date=17 October 2012|newspaper=The Guardian|archive-date=17 September 2013|archive-url=https://web.archive.org/web/20130917220225/http://www.theguardian.com/theguardian/2010/nov/08/harry-fensom-obituary|url-status=live}}</ref>

[[File:Eniac.jpg|thumb|upright=1.15|left|[[ENIAC]] was the first [[Electronics|electronic]], Turing-complete device, and performed ballistics trajectory calculations for the [[United States Army]].]]
The [[ENIAC]]<ref>John Presper Eckert Jr. and John W. Mauchly, Electronic Numerical Integrator and Computer, United States Patent Office, US Patent 3,120,606, filed 26 June 1947, issued 4 February 1964, and invalidated 19 October 1973 after court ruling on ''[[Honeywell v. Sperry Rand]]''.</ref> (Electronic Numerical Integrator and Computer) was the first electronic [[Computer programming|programmable]] computer built in the U.S. Although the ENIAC was similar to the Colossus, it was much faster, more flexible, and it was Turing-complete. Like the Colossus, a "program" on the ENIAC was defined by the [[State (computer science)|states]] of its patch cables and switches, a far cry from the [[stored program]] electronic machines that came later. Once a program was written, it had to be mechanically set into the machine with manual resetting of plugs and switches. The programmers of the ENIAC were six women, often known collectively as the "ENIAC girls".{{Sfn|Evans|2018|p=39}}{{Sfn|Light|1999|p=459}}

It combined the high speed of electronics with the ability to be programmed for many complex problems. It could add or subtract 5000 times a second, a thousand times faster than any other machine. It also had modules to multiply, divide, and square root. High speed memory was limited to 20 words (about 80 bytes). Built under the direction of [[John Mauchly]] and [[J. Presper Eckert]] at the University of Pennsylvania, ENIAC's development and construction lasted from 1943 to full operation at the end of 1945. The machine was huge, weighing 30 tons, using 200 kilowatts of electric power and contained over 18,000 vacuum tubes, 1,500 relays, and hundreds of thousands of resistors, capacitors, and inductors.<ref name="Eniac">{{cite web|url=http://www.techiwarehouse.com/engine/a046ee08/Generations-of-Computer|title=Generations of Computer|publisher=techiwarehouse.com|access-date=7 January 2014|archive-url=https://web.archive.org/web/20150702211455/http://www.techiwarehouse.com/engine/a046ee08/Generations-of-Computer/|archive-date=2 July 2015}}</ref>

=== Modern computers ===

==== Concept of modern computer ====
The principle of the modern computer was proposed by [[Alan Turing]] in his seminal 1936 paper,<ref>{{cite journal|doi=10.1112/plms/s2-42.1.230|last=Turing|first=A. M.|year=1937|title=On Computable Numbers, with an Application to the Entscheidungsproblem|journal=Proceedings of the London Mathematical Society|series=2 |volume=42|number=1|pages=230–265|s2cid=73712 }}</ref> ''On Computable Numbers''. Turing proposed a simple device that he called "Universal Computing machine" and that is now known as a [[universal Turing machine]]. He proved that such a machine is capable of computing anything that is computable by executing instructions (program) stored on tape, allowing the machine to be programmable. The fundamental concept of Turing's design is the [[stored program]], where all the instructions for computing are stored in memory. [[John von Neumann|Von Neumann]] acknowledged that the central concept of the modern computer was due to this paper.<ref>{{cite book |last=Copeland |first=Jack |author-link=Jack Copeland |year=2004 |title=The Essential Turing |quote-page=22|quote=von Neumann&nbsp;... firmly emphasized to me, and to others I am sure, that the fundamental conception is owing to Turing—insofar as not anticipated by Babbage, Lovelace and others.}} Letter by [[Stanley Frankel]] to [[Brian Randell]], 1972.</ref> Turing machines are to this day a central object of study in [[theory of computation]]. Except for the limitations imposed by their finite memory stores, modern computers are said to be [[Turing completeness|Turing-complete]], which is to say, they have [[algorithm]] execution capability equivalent to a universal Turing machine.

==== Stored programs ====
{{Main|Stored-program computer}}
[[File:SSEM Manchester museum close up.jpg|right|thumb|upright=1.15|alt=Three tall racks containing electronic circuit boards|A section of the reconstructed [[Manchester Baby]], the first electronic [[stored-program computer]]]]
Early computing machines had fixed programs. Changing its function required the re-wiring and re-structuring of the machine.<ref name="Copeland2006" /> With the proposal of the stored-program computer this changed. A stored-program computer includes by design an [[instruction set]] and can store in memory a set of instructions (a [[computer program|program]]) that details the [[computation]]. The theoretical basis for the stored-program computer was laid out by [[Alan Turing]] in his 1936 paper. In 1945, Turing joined the [[National Physical Laboratory (United Kingdom)|National Physical Laboratory]] and began work on developing an electronic stored-program digital computer. His 1945 report "Proposed Electronic Calculator" was the first specification for such a device. John von Neumann at the [[University of Pennsylvania]] also circulated his ''[[First Draft of a Report on the EDVAC]]'' in 1945.<ref name="stanf" />

The [[Manchester Baby]] was the world's first [[stored-program computer]]. It was built at the [[University of Manchester]] in England by [[Frederic Calland Williams|Frederic C. Williams]], [[Tom Kilburn]] and [[Geoff Tootill]], and ran its first program on 21 June 1948.<ref>{{cite journal |last=Enticknap |first=Nicholas |title=Computing's Golden Jubilee |journal=Resurrection |issue=20 |date=Summer 1998 |url=http://www.cs.man.ac.uk/CCS/res/res20.htm#d |issn=0958-7403 |access-date=19 April 2008 |archive-url=https://web.archive.org/web/20120109142655/http://www.cs.man.ac.uk/CCS/res/res20.htm#d |archive-date=9 January 2012  }}</ref> It was designed as a [[testbed]] for the [[Williams tube]], the first [[Random-access memory|random-access]] digital storage device.<ref>{{cite journal|title=Early computers at Manchester University|journal=Resurrection|volume=1|issue=4|date=Summer 1992|url=http://www.cs.man.ac.uk/CCS/res/res04.htm#g|issn=0958-7403|access-date=7 July 2010|archive-url=https://web.archive.org/web/20170828010743/http://www.cs.man.ac.uk/CCS/res/res04.htm#g|archive-date=28 August 2017}}</ref> 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.<ref>{{cite web|url=http://www.computer50.org/mark1/contemporary.html|title=Early Electronic Computers (1946–51)|publisher=University of Manchester|access-date=16 November 2008|archive-url=https://web.archive.org/web/20090105031620/http://www.computer50.org/mark1/contemporary.html|archive-date=5 January 2009}}</ref> As soon as the Baby had demonstrated the feasibility of its design, a project began at the university to develop it into a practically useful computer, the [[Manchester Mark 1]].

The Mark 1 in turn quickly became the prototype for the [[Ferranti Mark 1]], the world's first commercially available general-purpose computer.<ref name=NapperMK1>{{cite web |last=Napper |first=R. B. E. |title=Introduction to the Mark 1 |url=http://www.computer50.org/mark1/mark1intro.html |publisher=The University of Manchester |access-date=4 November 2008  |archive-url=https://web.archive.org/web/20081026080604/http://www.computer50.org/mark1/mark1intro.html |archive-date=26 October 2008 }}</ref> Built by [[Ferranti]], it was delivered to the University of Manchester in February 1951. At least seven of these later machines were delivered between 1953 and 1957, one of them to [[Royal Dutch Shell|Shell]] labs in [[Amsterdam]].<ref>{{cite web|publisher=[[Computer Conservation Society]]|title=Our Computer Heritage Pilot Study: Deliveries of Ferranti Mark I and Mark I Star computers|url=http://www.ourcomputerheritage.org/wp/|archive-url=https://web.archive.org/web/20161211201840/http://www.ourcomputerheritage.org/wp/|archive-date=11 December 2016|access-date=9 January 2010}}</ref> In October 1947 the directors of British catering company [[J. Lyons and Co.|J. Lyons & Company]] decided to take an active role in promoting the commercial development of computers. Lyons's [[LEO computer|LEO I]] computer, modelled closely on the Cambridge [[Electronic Delay Storage Automatic Calculator|EDSAC]] of 1949, became operational in April 1951<ref>{{cite web |last=Lavington |first=Simon |title=A brief history of British computers: the first 25 years (1948–1973). |publisher=[[British Computer Society]] |url=http://www.bcs.org/server.php? |access-date=10 January 2010 |archive-date=5 July 2010 |archive-url=https://web.archive.org/web/20100705050757/http://www.bcs.org/server.php  }}</ref> and ran the world's first routine office computer [[job (software)|job]].

==== Transistors ====
{{Main|Transistor|History of the transistor}}
{{Further|Transistor computer|MOSFET}}
<!-- [[Second generation of computers]] redirects here -->
[[File:Transistor-die-KSY34.jpg|thumb|right|[[Bipolar junction transistor]] (BJT)]]
The concept of a [[field-effect transistor]] was proposed by [[Julius Edgar Lilienfeld]] in 1925. [[John Bardeen]] and [[Walter Brattain]], while working under [[William Shockley]] at [[Bell Labs]], built the first working [[transistor]], the [[point-contact transistor]], in 1947, which was followed by Shockley's [[bipolar junction transistor]] in 1948.<ref name="Lee">{{cite book |last1=Lee |first1=Thomas H. |title=The Design of CMOS Radio-Frequency Integrated Circuits |date=2003 |publisher=[[Cambridge University Press]] |isbn=978-1-139-64377-1 |url=https://web.stanford.edu/class/archive/ee/ee214/ee214.1032/Handouts/HO2.pdf |access-date=31 July 2019 |archive-date=9 December 2019 |archive-url=https://web.archive.org/web/20191209032130/https://web.stanford.edu/class/archive/ee/ee214/ee214.1032/Handouts/HO2.pdf  }}</ref><ref name="Puers">{{cite book |last1=Puers |first1=Robert |last2=Baldi |first2=Livio |last3=Voorde |first3=Marcel Van de |last4=Nooten |first4=Sebastiaan E. van |title=Nanoelectronics: Materials, Devices, Applications, 2 Volumes |date=2017 |publisher=[[John Wiley & Sons]] |isbn=978-3-527-34053-8 |page=14 |url={{GBurl|id=JOqVDgAAQBAJ|p=14}} |access-date=31 July 2019 }}</ref> From 1955 onwards, transistors replaced [[vacuum tube]]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 transistor]]s were much more reliable than vacuum tubes and had longer, indefinite, service life. Transistorized computers could contain tens of thousands of binary logic circuits in a relatively compact space. However, early junction transistors were relatively bulky devices that were difficult to manufacture on a [[mass-production]] basis, which limited them to a number of specialized applications.<ref name="Moskowitz">{{cite book |last1=Moskowitz |first1=Sanford L. |title=Advanced Materials Innovation: Managing Global Technology in the 21st century |date=2016 |publisher=[[John Wiley & Sons]] |isbn=978-0-470-50892-3 |pages=165–167 |url={{GBurl|id=2STRDAAAQBAJ|p=165}} |access-date=28 August 2019 }}</ref>

At the [[University of Manchester]], a team under the leadership of [[Tom Kilburn]] designed and built a machine using the newly developed transistors instead of valves.{{sfn|Lavington|1998|pp=34–35}} Their first [[transistor computer|transistorized computer]] and the first in the world, was [[Manchester computers#Transistor Computer|operational by 1953]], and a second version was completed there in April 1955. However, the machine did make use of valves to generate its 125&nbsp;kHz clock waveforms and in the circuitry to read and write on its magnetic [[drum memory]], so it was not the first completely transistorized computer. That distinction goes to the [[Harwell CADET]] of 1955,<ref name="ieeexplore.ieee">{{cite journal |last=Cooke-Yarborough |first=E. H. |date=June 1998 |title=Some early transistor applications in the UK |url=https://ieeexplore.ieee.org/document/689507 |url-status=dead |journal=Engineering Science & Education Journal |volume=7 |issue=3 |pages=100–106 |doi=10.1049/esej:19980301 |doi-broken-date=7 December 2024 |issn=0963-7346 |archive-url=https://web.archive.org/web/20201108041817/https://ieeexplore.ieee.org/document/689507 |archive-date=8 November 2020 |access-date=7 June 2009|url-access=subscription }} {{subscription required}}.</ref> built by the electronics division of the [[Atomic Energy Research Establishment]] at [[Harwell, Oxfordshire|Harwell]].<ref name="ieeexplore.ieee" /><ref>{{cite book |last=Cooke-Yarborough |first=E. H. |title=Introduction to Transistor Circuits |publisher=Oliver and Boyd |year=1957 |location=Edinburgh, Scotland |page=139}}</ref>

[[File:MOSFET Structure.svg|thumb|right|[[MOSFET]] (MOS transistor), 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).]]

The [[MOSFET|metal–oxide–silicon field-effect transistor]] (MOSFET), also known as the MOS transistor, was invented at Bell Labs between 1955 and 1960<ref name=":03">{{Cite journal |last1=Huff |first1=Howard |last2=Riordan |first2=Michael |date=2007-09-01 |title=Frosch and Derick: Fifty Years Later (Foreword) |url=https://iopscience.iop.org/article/10.1149/2.F02073IF |journal=The Electrochemical Society Interface |volume=16 |issue=3 |pages=29 |doi=10.1149/2.F02073IF |issn=1064-8208|url-access=subscription }}</ref><ref>{{Cite journal |last1=Frosch |first1=C. J. |last2=Derick |first2=L |date=1957 |title=Surface Protection and Selective Masking during Diffusion in Silicon |url=https://iopscience.iop.org/article/10.1149/1.2428650 |journal=Journal of the Electrochemical Society |language=en |volume=104 |issue=9 |pages=547 |doi=10.1149/1.2428650|url-access=subscription }}</ref><ref>{{Cite journal |last=Kahng |first=D. |date=1961 |title=Silicon-Silicon Dioxide Surface Device |url=https://doi.org/10.1142/9789814503464_0076 |journal=Technical Memorandum of Bell Laboratories |pages=583–596 |doi=10.1142/9789814503464_0076 |isbn=978-981-02-0209-5|url-access=subscription }}</ref><ref>{{Cite book |last=Lojek |first=Bo |title=History of Semiconductor Engineering |date=2007 |publisher=Springer-Verlag Berlin Heidelberg |isbn=978-3-540-34258-8 |location=Berlin, Heidelberg |page=321}}</ref><ref>{{Cite journal |last1=Ligenza |first1=J. R. |last2=Spitzer |first2=W. G. |date=1960 |title=The mechanisms for silicon oxidation in steam and oxygen |url=https://linkinghub.elsevier.com/retrieve/pii/0022369760902195 |journal=Journal of Physics and Chemistry of Solids |language=en |volume=14 |pages=131–136 |bibcode=1960JPCS...14..131L |doi=10.1016/0022-3697(60)90219-5|url-access=subscription }}</ref><ref name="Lojek12023">{{cite book |last1=Lojek |first1=Bo |title=History of Semiconductor Engineering |date=2007 |publisher=[[Springer Science & Business Media]] |isbn=9783540342588 |page=120}}</ref> and was the first truly compact transistor that could be miniaturized and mass-produced for a wide range of uses.<ref name="Moskowitz"/> With its [[MOSFET scaling|high scalability]],<ref>{{cite journal |last1=Motoyoshi |first1=M. |s2cid=29105721 |title=Through-Silicon Via (TSV) |journal=Proceedings of the IEEE |date=2009 |volume=97 |issue=1 |pages=43–48 |doi=10.1109/JPROC.2008.2007462 |issn=0018-9219}}</ref> and much lower power consumption and higher density than bipolar junction transistors,<ref>{{cite news |last=Young |first=Ian |date=12 December 2018 |title=Transistors Keep Moore's Law Alive |language=en-US |work=[[EETimes]] |url=https://www.eetimes.com/author.asp?section_id=36&doc_id=1334068 |url-status=live |access-date=18 July 2019 |archive-date=24 September 2019 |archive-url=https://web.archive.org/web/20190924091622/https://www.eetimes.com/author.asp?section_id=36 }}</ref> the MOSFET made it possible to build [[Very large-scale integration|high-density integrated circuits]].<ref name="computerhistory-transistor">{{cite web |last=Laws |first=David |date=4 December 2013 |title=Who Invented the Transistor? |url=https://www.computerhistory.org/atchm/who-invented-the-transistor/ |url-status=live |access-date=20 July 2019 |website=[[Computer History Museum]] |archive-date=13 December 2013 |archive-url=https://web.archive.org/web/20131213221601/https://www.computerhistory.org/atchm/who-invented-the-transistor/ }}</ref><ref name="Hittinger">{{cite journal |last1=Hittinger |first1=William C. |title=Metal-Oxide-Semiconductor Technology |journal=Scientific American |date=1973 |volume=229 |issue=2 |pages=48–59 |issn=0036-8733|jstor=24923169 |doi=10.1038/scientificamerican0873-48 |bibcode=1973SciAm.229b..48H }}</ref> In addition to data processing, it also enabled the practical use of MOS transistors as [[memory cell (computing)|memory cell]] storage elements, leading to the development of MOS [[semiconductor memory]], which replaced earlier [[magnetic-core memory]] in computers. The MOSFET led to the [[microcomputer revolution]],<ref>{{cite book |last1=Malmstadt |first1=Howard V. |last2=Enke |first2=Christie G. |last3=Crouch |first3=Stanley R. |title=Making the Right Connections: Microcomputers and Electronic Instrumentation |date=1994 |publisher=[[American Chemical Society]] |isbn=978-0-8412-2861-0 |page=389 |url={{GBurl|id=lyJGAQAAIAAJ}} |quote=The relative simplicity and low power requirements of MOSFETs have fostered today's microcomputer revolution. |access-date=28 August 2019 }}</ref> and became the driving force behind the [[computer revolution]].<ref>{{cite book |author1-link=Jerry G. Fossum |last1=Fossum |first1=Jerry G. |last2=Trivedi |first2=Vishal P. |title=Fundamentals of Ultra-Thin-Body MOSFETs and FinFETs |date=2013 |publisher=[[Cambridge University Press]] |isbn=978-1-107-43449-3 |page=vii |url={{GBurl|id=zZJfAAAAQBAJ|pg=PR7}} |access-date=28 August 2019 }}</ref><ref name="uspto">{{cite web |last=Marriott |first=J. W. |date=June 10, 2019 |title=Remarks by Director Iancu at the 2019 International Intellectual Property Conference |url=https://www.uspto.gov/about-us/news-updates/remarks-director-iancu-2019-international-intellectual-property-conference |archive-url=https://web.archive.org/web/20191217200937/https://www.uspto.gov/about-us/news-updates/remarks-director-iancu-2019-international-intellectual-property-conference |archive-date=17 December 2019 |access-date=20 July 2019 |website=[[United States Patent and Trademark Office]]}}</ref> The MOSFET is the most widely used transistor in computers,<ref name="kahng">{{cite web |title=Dawon Kahng |url=https://www.invent.org/inductees/dawon-kahng |url-status=live |access-date=27 June 2019 |website=[[National Inventors Hall of Fame]] |archive-date=27 October 2019 |archive-url=https://web.archive.org/web/20191027062651/https://www.invent.org/inductees/dawon-kahng }}</ref><ref name="atalla">{{cite web|title=Martin Atalla in Inventors Hall of Fame, 2009|url=https://www.invent.org/inductees/martin-john-m-atalla|access-date=21 June 2013|archive-date=19 September 2019|archive-url=https://web.archive.org/web/20190919204631/https://www.invent.org/inductees/martin-john-m-atalla|url-status=live}}</ref> and is the fundamental building block of [[digital electronics]].<ref name="triumph">{{cite AV media |title=Triumph of the MOS Transistor |url=https://www.youtube.com/watch?v=q6fBEjf9WPw |archive-url=https://web.archive.org/web/20210818215224/https://www.youtube.com/watch?v=q6fBEjf9WPw |archive-date=2021-08-18 |via=YouTube |publisher=[[Computer History Museum]] |access-date=21 July 2019 |date=6 August 2010}}</ref>

==== Integrated circuits ====
{{Main|Integrated circuit|Invention of the integrated circuit}}
{{Further|Planar process|Microprocessor}}

[[File:MOS 6502A.jpg|thumb|Integrated circuits are typically packaged in plastic, metal, or ceramic cases to protect the IC from damage and for ease of assembly.]]
The next great advance in computing power came with the advent of the [[integrated circuit]] (IC).
The idea of the integrated circuit was first conceived by a radar scientist working for the [[Royal Radar Establishment]] of the [[Ministry of Defence (United Kingdom)|Ministry of Defence]], [[Geoffrey Dummer|Geoffrey W.A. Dummer]]. Dummer presented the first public description of an integrated circuit at the Symposium on Progress in Quality Electronic Components in [[Washington, D.C.|Washington,&nbsp;D.C.]], on 7 May 1952.<ref>[http://www.epn-online.com/page/22909/the-hapless-tale-of-geoffrey-dummer-this-is-the-sad-.html "The Hapless Tale of Geoffrey Dummer"] {{webarchive |url=https://web.archive.org/web/20130511181443/http://www.epn-online.com/page/22909/the-hapless-tale-of-geoffrey-dummer-this-is-the-sad-.html |date=11 May 2013 }}, (n.d.), (HTML), ''Electronic Product News'', accessed 8 July 2008.</ref>

The first working ICs were invented by [[Jack Kilby]] at [[Texas Instruments]] and [[Robert Noyce]] at [[Fairchild Semiconductor]].<ref>{{Cite web|first=Jack|last=Kilby|author-link=Jack Kilby|title=Nobel lecture|publisher=Nobel Foundation|year=2000|location=Stockholm|url=http://nobelprize.org/nobel_prizes/physics/laureates/2000/kilby-lecture.pdf|access-date=15 May 2008|archive-date=29 May 2008|archive-url=https://web.archive.org/web/20080529024119/http://nobelprize.org/nobel_prizes/physics/laureates/2000/kilby-lecture.pdf|url-status=live}}</ref> Kilby recorded his initial ideas concerning the integrated circuit in July 1958, successfully demonstrating the first working integrated example on 12 September 1958.<ref name="TIJackBuilt">[http://www.ti.com/corp/docs/kilbyctr/jackbuilt.shtml ''The Chip that Jack Built''] {{Webarchive|url=https://web.archive.org/web/20150501073820/http://www.ti.com/corp/docs/kilbyctr/jackbuilt.shtml |date=1 May 2015 }}, (c. 2008), (HTML), Texas Instruments, Retrieved 29 May 2008.</ref> In his patent application of 6 February 1959, Kilby described his new device as "a body of semiconductor material&nbsp;... wherein all the components of the electronic circuit are completely integrated".<ref>Jack S. Kilby, Miniaturized Electronic Circuits, United States Patent Office, US Patent 3,138,743, filed 6 February 1959, issued 23 June 1964.</ref><ref>{{cite book |last=Winston |first=Brian |title=Media Technology and Society: A History: From the Telegraph to the Internet |url={{GBurl|id=gfeCXlElJTwC|p=221}} |year=1998 |publisher=Routledge |isbn=978-0-415-14230-4 |page=221 |access-date=6 June 2020}}</ref> However, Kilby's invention was a [[hybrid integrated circuit]] (hybrid IC), rather than a [[monolithic integrated circuit]] (IC) chip.<ref name="Saxena140">{{cite book |last1=Saxena |first1=Arjun N. |title=Invention of Integrated Circuits: Untold Important Facts |date=2009 |publisher=[[World Scientific]] |isbn=978-981-281-445-6 |page=140 |url={{GBurl|id=-3lpDQAAQBAJ|p=140}} |access-date=28 August 2019 }}</ref> Kilby's IC had external wire connections, which made it difficult to mass-produce.<ref name="nasa">{{cite web |title=Integrated circuits |url=https://www.hq.nasa.gov/alsj/ic-pg3.html |website=[[NASA]] |access-date=13 August 2019 |archive-date=21 July 2019 |archive-url=https://web.archive.org/web/20190721173218/https://www.hq.nasa.gov/alsj/ic-pg3.html |url-status=live }}</ref>

Noyce also came up with his own idea of an integrated circuit half a year later than Kilby.<ref>[[Robert Noyce]]'s Unitary circuit, {{Ref patent |country=US |number=2981877|status=patent|gdate=1961-04-25|title=Semiconductor device-and-lead structure |assign1=[[Fairchild Semiconductor Corporation]]}}.</ref> Noyce's invention was the first true monolithic IC chip.<ref name="computerhistory1959">{{cite web |title=1959: Practical Monolithic Integrated Circuit Concept Patented |url=https://www.computerhistory.org/siliconengine/practical-monolithic-integrated-circuit-concept-patented/ |website=[[Computer History Museum]] |access-date=13 August 2019 |archive-date=24 October 2019 |archive-url=https://web.archive.org/web/20191024144046/https://www.computerhistory.org/siliconengine/practical-monolithic-integrated-circuit-concept-patented/ |url-status=live }}</ref><ref name="nasa"/> His chip solved many practical problems that Kilby's had not. Produced at Fairchild Semiconductor, it was made of [[silicon]], whereas Kilby's chip was made of [[germanium]]. Noyce's monolithic IC was [[semiconductor device fabrication|fabricated]] using the [[planar process]], developed by his colleague [[Jean Hoerni]] in early 1959. In turn, the planar process was based on [[Carl Frosch]] and Lincoln Derick work on semiconductor surface passivation by silicon dioxide.<ref>{{Cite journal |last1=Frosch |first1=C. J. |last2=Derick |first2=L. |date=1957 |title=Surface Protection and Selective Masking during Diffusion in Silicon |url=https://iopscience.iop.org/article/10.1149/1.2428650 |journal=Journal of the Electrochemical Society |language=en |volume=104 |issue=9 |pages=547 |doi=10.1149/1.2428650|url-access=subscription }}</ref><ref>{{Cite patent|number=US2802760A|title=Oxidation of semiconductive surfaces for controlled diffusion|gdate=1957-08-13|invent1=Lincoln|invent2=Frosch|inventor1-first=Derick|inventor2-first=Carl J.|url=https://patents.google.com/patent/US2802760A}}.</ref><ref name="Moskowitz4">{{cite book |last1=Moskowitz |first1=Sanford L. |url=https://books.google.com/books?id=2STRDAAAQBAJ&pg=PA168 |title=Advanced Materials Innovation: Managing Global Technology in the 21st century |date=2016 |publisher=[[John Wiley & Sons]] |isbn=978-0-470-50892-3 |page=168}}</ref><ref>{{cite book |last1=Lécuyer |first1=Christophe |url=https://books.google.com/books?id=LaZpUpkG70QC&pg=PA62 |title=Makers of the Microchip: A Documentary History of Fairchild Semiconductor |last2=Brook |first2=David C. |last3=Last |first3=Jay |date=2010 |publisher=MIT Press |isbn=978-0-262-01424-3 |pages=62–63}}</ref><ref>{{cite book |last1=Claeys |first1=Cor L. |url=https://books.google.com/books?id=bu22JNYbE5MC&pg=PA27 |title=ULSI Process Integration III: Proceedings of the International Symposium |date=2003 |publisher=[[The Electrochemical Society]] |isbn=978-1-56677-376-8 |pages=27–30}}</ref><ref name="Lojek1204">{{cite book |last1=Lojek |first1=Bo |title=History of Semiconductor Engineering |date=2007 |publisher=[[Springer Science & Business Media]] |isbn=9783540342588 |page=120}}</ref>

Modern monolithic ICs are predominantly MOS ([[metal–oxide–semiconductor]]) integrated circuits, built from [[MOSFET]]s (MOS transistors).<ref name="Kuo">{{cite journal |last1=Kuo |first1=Yue |title=Thin Film Transistor Technology—Past, Present, and Future |journal=The Electrochemical Society Interface |date=1 January 2013 |volume=22 |issue=1 |pages=55–61 |doi=10.1149/2.F06131if |bibcode=2013ECSIn..22a..55K |url=https://www.electrochem.org/dl/interface/spr/spr13/spr13_p055_061.pdf |issn=1064-8208 |doi-access=free |access-date=31 July 2019 |archive-date=29 August 2017 |archive-url=https://web.archive.org/web/20170829042321/http://www.electrochem.org/dl/interface/spr/spr13/spr13_p055_061.pdf |url-status=live }}</ref> The earliest experimental MOS IC to be fabricated was a 16-transistor chip built by Fred Heiman and Steven Hofstein at [[RCA]] in 1962.<ref name="computerhistory-digital">{{cite web |title=Tortoise of Transistors Wins the Race – CHM Revolution |url=https://www.computerhistory.org/revolution/digital-logic/12/279 |website=[[Computer History Museum]] |access-date=22 July 2019 |archive-date=10 March 2020 |archive-url=https://web.archive.org/web/20200310142421/https://www.computerhistory.org/revolution/digital-logic/12/279 |url-status=live }}</ref> [[General Microelectronics]] later introduced the first commercial MOS IC in 1964,<ref>{{cite web|url=http://www.computerhistory.org/semiconductor/timeline/1964-Commecial.html|title=1964 – First Commercial MOS IC Introduced|website=[[Computer History Museum]]|access-date=31 July 2019|archive-date=22 December 2015|archive-url=https://web.archive.org/web/20151222203215/http://www.computerhistory.org/semiconductor/timeline/1964-Commecial.html|url-status=live}}</ref> developed by Robert Norman.<ref name="computerhistory-digital"/> Following the development of the [[self-aligned gate]] (silicon-gate) MOS transistor by Robert Kerwin, [[Donald L. Klein|Donald Klein]] and John Sarace at Bell Labs in 1967, the first [[silicon-gate]] MOS IC with [[self-aligned gate]]s was developed by [[Federico Faggin]] at Fairchild Semiconductor in 1968.<ref>{{cite web |title=1968: Silicon Gate Technology Developed for ICs |url=https://www.computerhistory.org/siliconengine/silicon-gate-technology-developed-for-ics/ |website=[[Computer History Museum]] |access-date=22 July 2019 |archive-date=29 July 2020 |archive-url=https://web.archive.org/web/20200729145834/https://www.computerhistory.org/siliconengine/silicon-gate-technology-developed-for-ics/ |url-status=live }}</ref> The MOSFET has since become the most critical device component in modern ICs.<ref name="Kuo" />

[[File:MOS 6502 die.jpg|thumb|[[Die (integrated circuit)|Die]] photograph of a [[MOS Technology 6502|MOS 6502]], an early 1970s microprocessor integrating 3500 transistors on a single chip]]
The development of the MOS integrated circuit led to the invention of the [[microprocessor]],<ref name="computerhistory1971">{{cite web |title=1971: Microprocessor Integrates CPU Function onto a Single Chip |url=https://www.computerhistory.org/siliconengine/microprocessor-integrates-cpu-function-onto-a-single-chip/ |website=[[Computer History Museum]] |access-date=22 July 2019 |archive-date=12 August 2021 |archive-url=https://web.archive.org/web/20210812104243/https://www.computerhistory.org/siliconengine/microprocessor-integrates-cpu-function-onto-a-single-chip/ |url-status=live }}</ref><ref name="Colinge2016">{{cite book |last1=Colinge |first1=Jean-Pierre |last2=Greer |first2=James C. |title=Nanowire Transistors: Physics of Devices and Materials in One Dimension |date=2016 |publisher=[[Cambridge University Press]] |isbn=978-1-107-05240-6 |page=2 |url={{GBurl|id=FvjUCwAAQBAJ|p=2}} |access-date=31 July 2019 }}</ref> 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]],<ref>{{Cite web|title=Intel's First Microprocessor—the Intel 4004 |publisher=Intel Corp. |date=November 1971 |url=http://www.intel.com/museum/archives/4004.htm |access-date=17 May 2008  |archive-date=13 May 2008 |archive-url=https://web.archive.org/web/20080513221700/http://www.intel.com/museum/archives/4004.htm}}</ref> designed and realized by Federico Faggin with his silicon-gate MOS IC technology,<ref name="computerhistory1971"/> along with [[Marcian Hoff|Ted Hoff]], [[Masatoshi Shima]] and [[Stanley Mazor]] at [[Intel]].{{efn|The Intel 4004 (1971) die was 12&nbsp;mm<sup>2</sup>, composed of 2300 transistors; by comparison, the Pentium Pro was 306&nbsp;mm<sup>2</sup>, composed of 5.5&nbsp;million transistors.<ref>{{cite book |last1=Patterson |first1=David |last2=Hennessy |first2=John |year=1998 |title=Computer Organization and Design |location=San Francisco |publisher=[[Morgan Kaufmann]] |isbn=978-1-55860-428-5 |pages=[https://archive.org/details/computerorganiz000henn/page/27 27–39] |url=https://archive.org/details/computerorganiz000henn}}</ref>}}<ref name="ieee">[[Federico Faggin]], [https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=4776530 The Making of the First Microprocessor], ''IEEE Solid-State Circuits Magazine'', Winter 2009, [[IEEE Xplore]].</ref> In the early 1970s, MOS IC technology enabled the [[very large-scale integration|integration]] of more than 10,000 transistors on a single chip.<ref name="Hittinger"/>

[[System on a Chip]] (SoCs) are complete computers on a [[microchip]] (or chip) the size of a coin.<ref name="networkworld.com">{{Cite web|url=https://www.networkworld.com/article/3154386/7-dazzling-smartphone-improvements-with-qualcomms-snapdragon-835-chip.html|title=7 dazzling smartphone improvements with Qualcomm's Snapdragon 835 chip|date=3 January 2017|access-date=5 April 2019|archive-date=30 September 2019|archive-url=https://web.archive.org/web/20190930224934/https://www.networkworld.com/article/3154386/7-dazzling-smartphone-improvements-with-qualcomms-snapdragon-835-chip.html|url-status=live}}</ref> They may or may not have integrated [[random-access memory|RAM]] and [[flash memory]]. If not integrated, the RAM is usually placed directly above (known as [[Package on package]]) or below (on the opposite side of the [[circuit board]]) the SoC, and the flash memory is usually placed right next to the SoC. This is done to improve data transfer speeds, as the data signals do not have to travel long distances. Since ENIAC in 1945, computers have advanced enormously, with modern SoCs (such as the Snapdragon 865) being the size of a coin while also being hundreds of thousands of times more powerful than ENIAC, integrating billions of transistors, and consuming only a few watts of power.

=== Mobile computers ===
The first [[portable computer|mobile computers]] were heavy and ran from mains power. The {{convert|50|lb|abbr=on}} [[IBM 5100]] was an early example. Later portables such as the [[Osborne 1]] and [[Compaq Portable]] were considerably lighter but still needed to be plugged in. The first laptops, such as the [[Grid Compass]], removed this requirement by incorporating batteries – and with the continued miniaturization of computing resources and advancements in portable battery life, portable computers grew in popularity in the 2000s.<ref>{{cite news|url=https://arstechnica.com/uncategorized/2008/12/global-notebook-shipments-finally-overtake-desktops/|title=Global notebook shipments finally overtake desktops|work=Ars Technica|first=David|last=Chartier|date=23 December 2008|access-date=14 June 2017|archive-date=4 July 2017|archive-url=https://web.archive.org/web/20170704180604/https://arstechnica.com/uncategorized/2008/12/global-notebook-shipments-finally-overtake-desktops/|url-status=live}}</ref> The same developments allowed manufacturers to integrate computing resources into cellular mobile phones by the early 2000s.

These [[smartphone]]s and [[tablet computer|tablets]] run on a variety of operating systems and recently became the dominant computing device on the market.<ref>{{cite web|author=IDC|title=Growth Accelerates in the Worldwide Mobile Phone and Smartphone Markets in the Second Quarter, According to IDC|date=25 July 2013|url=http://www.idc.com/getdoc.jsp?containerId=prUS24239313|archive-url=https://web.archive.org/web/20140626022208/http://www.idc.com/getdoc.jsp?containerId=prUS24239313|archive-date=26 June 2014}}</ref> These are powered by [[System on a Chip]] (SoCs), which are complete computers on a microchip the size of a coin.<ref name="networkworld.com"/>

== Types ==
{{See also|Classes of computers}}
Computers can be classified in a number of different ways, including:

=== By architecture ===
* [[Analog computer]]
* Digital computer
* [[Hybrid computer]]
* [[Harvard architecture]]
* [[Von Neumann architecture]]
* [[Complex instruction set computer]]
* [[Reduced instruction set computer]]

=== By size, form-factor and purpose ===
{{see also|List of computer size categories}}

* [[Supercomputer]]
* [[Mainframe computer]]
* [[Minicomputer]] (term no longer used),<ref>{{Cite web|url=https://books.google.com/ngrams/graph?content=Minicomputer&year_start=1800&year_end=2019&corpus=26&smoothing=3&direct_url=t1;,Minicomputer;,c0|title=Google Books Ngram Viewer|website=books.google.com}}</ref> [[Midrange computer]]
* Server
** [[Server (computing)|Rackmount server]]
** [[Blade server]]
** [[Computer tower|Tower server]]
* Personal computer
** [[Workstation]]
** [[Microcomputer]] (term no longer used)<ref>{{Cite web|url=https://books.google.com/ngrams/graph?content=Microcomputer&year_start=1800&year_end=2019&corpus=26&smoothing=3&direct_url=t1;,Microcomputer;,c0|title=Google Books Ngram Viewer|website=books.google.com}}</ref>
*** [[Home computer]] (term fallen into disuse)<ref>{{Cite web|url=https://books.google.com/ngrams/graph?content=Home+computer&year_start=1800&year_end=2019&corpus=26&smoothing=3&direct_url=t1;,Home+computer;,c0|title=Google Books Ngram Viewer|website=books.google.com}}</ref>
** [[Desktop computer]]
*** [[Computer tower|Tower desktop]]
*** Slimline desktop
**** [[Multimedia computer]] ([[non-linear editing system]] computers, video editing PCs and the like, this term is no longer used)<ref>{{Cite web|url=https://books.google.com/ngrams/graph?content=Multimedia+computer&year_start=1800&year_end=2019&corpus=26&smoothing=3&direct_url=t1;,Multimedia+computer;,c0|title=Google Books Ngram Viewer|website=books.google.com}}</ref>
**** [[Gaming computer]]
*** [[All-in-one PC]]
*** [[Nettop]] ([[Small form factor (desktop and motherboard)|Small form factor PC]]s, Mini PCs)
*** [[Home theater PC]]
***  [[Keyboard computer]]
*** [[Portable computer]]
*** [[Thin client]]
*** [[Internet appliance]]
** [[Laptop|Laptop computer]]
*** [[Desktop replacement computer]]
*** [[Gaming computer#Gaming laptop computers|Gaming laptop]]
*** [[Rugged computer|Rugged laptop]]
*** [[2-in-1 PC]]
*** [[Ultrabook]]
*** [[Chromebook]]
*** [[Subnotebook]]
*** [[Smartbook]]
*** [[Netbook]]
** [[Mobile computing|Mobile computer]]
*** [[Tablet computer]]
*** [[Smartphone]]
*** [[Ultra-mobile PC]]
*** [[Pocket PC]]
*** [[Palmtop PC]]
*** [[Handheld PC]]
*** [[Pocket computer]]
** [[Wearable computer]]
*** [[Smartwatch]]
*** [[Smartglasses]]
* [[Single-board computer]]
* [[Plug computer]]
* [[Stick PC]]
* [[Programmable logic controller]]
* [[Computer-on-module]]
* [[System on module]]
* [[System in a package]]
* [[System-on-chip]] (Also known as an Application Processor or AP if it lacks circuitry such as radio circuitry)
* [[Microcontroller]]

=== Unconventional computers ===
{{Main|Human computer}}
{{See also|Harvard Computers}}

A computer does not need to be [[electronics|electronic]], nor even have a [[Central processing unit|processor]], nor [[Random-access memory|RAM]], nor even a [[hard disk]]. While popular usage of the word "computer" is synonymous with a personal electronic computer,{{efn|According to the ''[[Shorter Oxford English Dictionary]]'' (6th ed, 2007), the word ''computer'' dates back to the mid 17th century, when it referred to "A person who makes calculations; specifically a person employed for this in an observatory etc."}} a typical modern definition of a computer is: "''A device that computes'', especially a programmable [usually] electronic machine that performs high-speed mathematical or logical operations or that assembles, stores, correlates, or otherwise processes information."<ref>{{cite web |title=Definition of computer |url=http://thefreedictionary.com/computer |url-status=live |archive-url=http://arquivo.pt/wayback/20091226162252/http%3A//www.thefreedictionary.com/computer |archive-date=26 December 2009 |access-date=29 January 2012 |publisher=Thefreedictionary.com}}</ref> According to this definition, any device that ''processes information'' qualifies as a computer.

== Hardware ==
{{Main|Computer hardware|Computer hardware#Personal computer{{!}}Personal computer hardware|Central processing unit|Microprocessor}}[[File:Computer Components.webm|thumb|Video demonstrating the standard components of a "slimline" computer]]

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

=== History of computing hardware ===
{{Main|History of computing hardware}}
<!-- WARNING: Please be careful about modifying this table, especially if you are not familiar with Wikipedia table syntax. Make judicious use of the "Preview" button! -->
{| class="wikitable"
|-
| rowspan="2" | First generation<br />(mechanical/electromechanical) || Calculators || [[Pascal's calculator]], [[Arithmometer]], [[Difference engine]], [[Leonardo Torres y Quevedo#Analytical machines|Quevedo's analytical machines]]
|-
| Programmable devices || [[Jacquard loom]], [[Analytical engine]], [[Harvard Mark I|IBM ASCC/Harvard Mark I]], [[Harvard Mark II]], [[IBM SSEC]], [[Z1 (computer)|Z1]], [[Z2 (computer)|Z2]], [[Z3 (computer)|Z3]]
|-
| rowspan="2" | Second generation<br />(vacuum tubes) || Calculators || [[Atanasoff–Berry Computer]], [[IBM 604]], [[Remington Rand 409|UNIVAC 60]], [[Remington Rand 409|UNIVAC 120]]
|-
| [[List of vacuum-tube computers|Programmable devices]] || [[Colossus computer|Colossus]], [[ENIAC]], [[Manchester Baby]], [[EDSAC]], [[Manchester Mark 1]], [[Ferranti Pegasus]], [[Ferranti Mercury]], [[CSIRAC]], [[EDVAC]], [[UNIVAC I]], [[IBM 701]], [[IBM 702]], [[IBM 650]], [[Z22 (computer)|Z22]]
|-
| rowspan="3" | Third generation<br />(discrete [[transistor]]s and SSI, MSI, LSI [[integrated circuit]]s) || [[Mainframe computer|Mainframes]] || [[IBM 7090]], [[IBM 7080]], [[IBM System/360]], [[BUNCH]]
|-
| [[Minicomputer]] || [[HP 2100|HP 2116A]], [[IBM System/32]], [[IBM System/36]], [[LINC]], [[PDP-8]], [[PDP-11]]
|-
| [[Desktop Computer]] || [[HP 9100]]
|-
| rowspan="8" | Fourth generation<br />([[VLSI]] integrated circuits) || Minicomputer || [[VAX]], [[IBM AS/400]]
|-
| [[4-bit computing|4-bit]] microcomputer || [[Intel 4004]], [[Intel 4040]]
|-
| [[8-bit computing|8-bit]] microcomputer || [[Intel 8008]], [[Intel 8080]], [[Motorola 6800]], [[Motorola 6809]], [[MOS Technology 6502]], [[Zilog Z80]]
|-
| [[16-bit computing|16-bit]] [[microcomputer]]|| [[Intel 8088]], [[Zilog Z8000]], [[WDC 65816/65802]]
|-
| [[32-bit computing|32-bit]] microcomputer || [[Intel 80386]], [[Pentium]], [[Motorola 68000]], [[ARMv7|ARM]]
|-
| [[64-bit computing|64-bit]] microcomputer{{efn|Most major 64-bit [[instruction set]] architectures are extensions of earlier designs. All of the architectures listed in this table, except for Alpha, existed in 32-bit forms before their 64-bit incarnations were introduced.}}|| [[DEC Alpha|Alpha]], [[MIPS architecture|MIPS]], [[PA-RISC]], [[PowerPC]], [[SPARC]], [[x86-64]], [[ARMv8-A]]
|-
| [[Embedded system|Embedded computer]] || [[Intel 8048]], [[Intel 8051]]
|-
| Personal computer || [[Desktop computer]], [[Home computer]], Laptop computer, [[Personal digital assistant]] (PDA), [[Portable computer]], [[tablet computer|Tablet PC]], [[Wearable computer]]
|-
| rowspan="6" | Theoretical/experimental || [[Quantum computer]] || [[IBM Q System One]]
|-
| [[Chemical computer]] ||
|-
| [[DNA computing]] ||
|-
| [[Photonic computing|Optical computer]] ||
|-
| [[Spintronics]]-based computer ||
|-
| [[Wetware computer|Wetware/Organic computer]] ||
|}

=== Other hardware topics ===

{| class="wikitable"
|-
| rowspan="3" | [[Peripheral]] device ([[input/output]]) || Input || [[Computer mouse|Mouse]], [[Computer keyboard|keyboard]], [[joystick]], [[image scanner]], [[webcam]], [[graphics tablet]], [[microphone]]
|-
| Output || [[computer monitor|Monitor]], [[Printer (computing)|printer]], [[Computer speakers|loudspeaker]]
|-
| Both || [[Floppy disk]] drive, [[hard disk drive]], [[optical disc]] drive, [[teleprinter]]
|-
| rowspan="2" | [[Bus (computing)|Computer buses]] || Short range || [[RS-232]], [[SCSI]], [[Peripheral Component Interconnect|PCI]], [[USB]]
|-
| Long range ([[computer network]]ing) || [[Ethernet]], [[Asynchronous Transfer Mode|ATM]], [[Fiber Distributed Data Interface|FDDI]]
|}

A general-purpose computer has four main components: the [[arithmetic logic unit]] (ALU), the [[control unit]], the [[Computer data storage|memory]], and the [[input and output devices]] (collectively termed I/O). These parts are interconnected by [[bus (computing)|buses]], often made of groups of [[wire]]s. Inside each of these parts are thousands to trillions of small [[electrical network|electrical circuits]] which can be turned off or on by means of an [[transistor|electronic switch]]. Each circuit represents a [[bit]] (binary digit) of information so that when the circuit is on it represents a "1", and when off it represents a "0" (in positive logic representation). The circuits are arranged in [[logic gate]]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]]
* [[Digital camera]]
* [[Graphics tablet]]
* [[Image scanner]]
* [[Joystick]]
* [[Microphone]]
* [[Computer mouse|Mouse]]
* [[Overlay keyboard]]
* [[Real-time clock]]
* [[Trackball]]
* [[Touchscreen]]
* [[Light pen]]

=== Output devices ===
The means through which computer gives output are known as output devices. Some examples of output devices are:
* [[Computer monitor]]
* [[Printer (computing)|Printer]]
* [[PC speaker]]
* [[Projector]]
* [[Sound card]]
* [[Graphics card]]

=== Control unit ===
{{Main|CPU design|Control unit}}
[[File:Mips32 addi.svg|thumb|upright=1.5|right|Diagram showing how a particular [[MIPS architecture]] instruction would be decoded by the control system]]

The [[control unit]] (often called a control system or central controller) manages the computer's various components; it reads and interprets (decodes) the program instructions, transforming them into control signals that activate other parts of the computer.{{efn|The control unit's role in interpreting instructions has varied somewhat in the past. Although the control unit is solely responsible for instruction interpretation in most modern computers, this is not always the case. Some computers have instructions that are partially interpreted by the control unit with further interpretation performed by another device. For example, [[EDVAC]], one of the earliest stored-program computers, used a central control unit that interpreted only four instructions. All of the arithmetic-related instructions were passed on to its arithmetic unit and further decoded there.}} Control systems in advanced computers may change the order of execution of some instructions to improve performance.

A key component common to all CPUs is the [[program counter]], a special memory cell (a [[processor register|register]]) that keeps track of which location in memory the next instruction is to be read from.{{efn|Instructions often occupy more than one memory address, therefore the program counter usually increases by the number of memory locations required to store one instruction.}}

The control system's function is as follows— this is a simplified description, and some of these steps may be performed concurrently or in a different order depending on the type of CPU:

# Read the code for the next instruction from the cell indicated by the program counter.
# Decode the numerical code for the instruction into a set of commands or signals for each of the other systems.
# Increment the program counter so it points to the next instruction.
# Read whatever data the instruction requires from cells in memory (or perhaps from an input device). The location of this required data is typically stored within the instruction code.
# Provide the necessary data to an ALU or register.
# If the instruction requires an ALU or specialized hardware to complete, instruct the hardware to perform the requested operation.
# Write the result from the ALU back to a memory location or to a register or perhaps an output device.
# Jump back to step (1).

Since the program counter is (conceptually) just another set of memory cells, it can be changed by calculations done in the ALU. Adding 100 to the program counter would cause the next instruction to be read from a place 100 locations further down the program. Instructions that modify the program counter are often known as "jumps" and allow for loops (instructions that are repeated by the computer) and often conditional instruction execution (both examples of [[control flow]]).

The sequence of operations that the control unit goes through to process an instruction is in itself like a short computer program, and indeed, in some more complex CPU designs, there is another yet smaller computer called a [[microsequencer]], which runs a [[microcode]] program that causes all of these events to happen.

=== Central processing unit (CPU) ===
{{Main|Central processing unit|Microprocessor}}

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

=== Arithmetic logic unit (ALU) ===
{{Main|Arithmetic logic unit}}

The ALU is capable of performing two classes of operations: arithmetic and logic.<ref>{{Cite book |author=Eck |first=David J. |title=The Most Complex Machine: A Survey of Computers and Computing |publisher=A K Peters, Ltd. |year=2000 |isbn=978-1-56881-128-4 |page=54}}</ref> The set of arithmetic operations that a particular ALU supports may be limited to addition and subtraction, or might include multiplication, division, [[trigonometry]] functions such as sine, cosine, etc., and [[square root]]s. Some can operate only on whole numbers ([[integer]]s) while others use [[floating point]] to represent [[real number]]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 [[Truth value|Boolean truth values]] (true or false) depending on whether one is equal to, greater than or less than the other ("is 64 greater than 65?"). Logic operations involve [[Boolean logic]]: [[logical conjunction|AND]], [[logical disjunction|OR]], [[Exclusive or|XOR]], and [[Negation|NOT]]. These can be useful for creating complicated [[conditional (programming)|conditional statements]] and processing [[Boolean logic]].

[[Superscalar]] computers may contain multiple ALUs, allowing them to process several instructions simultaneously.<ref>{{Cite book |author=Kontoghiorghes |first=Erricos John |title=Handbook of Parallel Computing and Statistics |publisher=CRC Press |year=2006 |isbn=978-0-8247-4067-2 |page=45}}</ref> [[Graphics processing unit|Graphics processors]] and computers with [[Single instruction, multiple data|SIMD]] and [[Multiple instruction, multiple data|MIMD]] features often contain ALUs that can perform arithmetic on [[Euclidean vector|vectors]] and [[Matrix (mathematics)|matrices]].

=== Memory ===
{{Main|Computer memory|Computer data storage}}
[[File:Magnetic core.jpg|thumb|right|[[Magnetic-core memory]] (using [[magnetic cores]]) was the [[computer memory]] of choice in the 1960s, until it was replaced by [[semiconductor memory]] (using [[MOSFET|MOS]] memory cells).]]

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 (computing)|memory cell]] is set up to store [[binary number]]s in groups of eight bits (called a [[byte]]). Each byte is able to represent 256 different numbers (2<sup>8</sup> = 256); either from 0 to 255 or −128 to +127. To store larger numbers, several consecutive bytes may be used (typically, two, four or eight). When negative numbers are required, they are usually stored in [[two's complement]] notation. Other arrangements are possible, but are usually not seen outside of specialized applications or historical contexts. A computer can store any kind of information in memory if it can be represented numerically. Modern computers have billions or even trillions of bytes of memory.

The CPU contains a special set of memory cells called [[Processor register|registers]] that can be read and written to much more rapidly than the main memory area. There are typically between two and one hundred registers depending on the type of CPU. Registers are used for the most frequently needed data items to avoid having to access main memory every time data is needed. As data is constantly being worked on, reducing the need to access main memory (which is often slow compared to the ALU and control units) greatly increases the computer's speed.

Computer main memory comes in two principal varieties:
* [[random-access memory]] or RAM
* [[read-only memory]] or ROM
RAM can be read and written to anytime the CPU commands it, but ROM is preloaded with data and software that never changes, therefore the CPU can only read from it. ROM is typically used to store the computer's initial start-up instructions. In general, the contents of RAM are erased when the power to the computer is turned off, but ROM retains its data indefinitely. In a PC, the ROM contains a specialized program called the [[BIOS]] that orchestrates loading the computer's [[operating system]] from the hard disk drive into RAM whenever the computer is turned on or reset. In [[embedded system|embedded computers]], which frequently do not have disk drives, all of the required software may be stored in ROM. Software stored in ROM is often called [[firmware]], because it is notionally more like hardware than software. [[Flash memory]] blurs the distinction between ROM and RAM, as it retains its data when turned off but is also rewritable. It is typically much slower than conventional ROM and RAM however, so its use is restricted to applications where high speed is unnecessary.{{efn|Flash memory also may only be rewritten a limited number of times before wearing out, making it less useful for heavy random access usage.{{sfn|Verma|Mielke|1988}} }}

In more sophisticated computers there may be one or more RAM [[CPU cache|cache memories]], which are slower than registers but faster than main memory. Generally computers with this sort of cache are designed to move frequently needed data into the cache automatically, often without the need for any intervention on the programmer's part.

=== Input/output (I/O) ===
{{Main|Input/output}}
[[File:HDDspin.JPG|thumb|right|[[Hard disk drive]]s are common storage devices used with computers.]]
I/O is the means by which a computer exchanges information with the outside world.<ref>{{Cite book |author=Eadie |first=Donald |title=Introduction to the Basic Computer |publisher=Prentice-Hall |year=1968 |page=12}}</ref> Devices that provide input or output to the computer are called [[peripheral]]s.<ref>{{Cite book |author=Barna |first1=Arpad |url=https://archive.org/details/introductiontomi0000barn/page/85 |title=Introduction to Microcomputers and the Microprocessors |last2=Porat |first2=Dan I. |publisher=Wiley |year=1976 |isbn=978-0-471-05051-3 |page=[https://archive.org/details/introductiontomi0000barn/page/85 85]}}</ref> On a typical personal computer, peripherals include input devices like the keyboard and [[Computer mouse|mouse]], and output devices such as the [[computer monitor|display]] and [[printer (computing)|printer]]. [[Hard disk drive]]s, [[floppy disk]] drives and [[optical disc drive]]s serve as both input and output devices. [[Computer network]]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]] might contain fifty or more tiny computers that perform the calculations necessary to display [[3D computer graphics|3D graphics]].{{Citation needed|date=December 2007}} Modern [[desktop computer]]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 ===
{{Main|Computer 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.<ref>{{Cite book |author=Peek |first1=Jerry |url=https://archive.org/details/learningunixoper00jerr/page/130 |title=Learning the UNIX Operating System: A Concise Guide for the New User |last2=Todino |first2=Grace |last3=Strang |first3=John |publisher=O'Reilly |year=2002 |isbn=978-0-596-00261-9 |page=[https://archive.org/details/learningunixoper00jerr/page/130 130]}}</ref> One means by which this is done is with a special signal called an [[interrupt]], which can periodically cause the computer to stop executing instructions where it was and do something else instead. By remembering where it was executing prior to the interrupt, the computer can return to that task later. If several programs are running "at the same time". Then the interrupt generator might be causing several hundred interrupts per second, causing a program switch each time. Since modern computers typically execute instructions several orders of magnitude faster than human perception, it may appear that many programs are running at the same time, even though only one is ever executing in any given instant. This method of multitasking is sometimes termed "time-sharing" since each program is allocated a "slice" of time in turn.<ref>{{Cite book |author=Davis |first=Gillian M. |title=Noise Reduction in Speech Applications |publisher=CRC Press |year=2002 |isbn=978-0-8493-0949-6 |page=111}}</ref>

Before the era of inexpensive computers, the principal use for multitasking was to allow many people to share the same computer. Seemingly, multitasking would cause a computer that is switching between several programs to run more slowly, in direct proportion to the number of programs it is running, but most programs spend much of their time waiting for slow input/output devices to complete their tasks. If a program is waiting for the user to click on the mouse or press a key on the keyboard, then it will not take a "time slice" until the [[event (computing)|event]] it is waiting for has occurred. This frees up time for other programs to execute so that many programs may be run simultaneously without unacceptable speed loss.

=== Multiprocessing ===
{{Main|Multiprocessing}}
[[File:Cray 2 Arts et Metiers dsc03940.jpg|thumb|upright=1.15|[[Cray]] designed many supercomputers that used multiprocessing heavily.]]
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]]s, [[mainframe computer]]s and [[server (computing)|servers]]. Multiprocessor and [[multi-core]] (multiple CPUs on a single integrated circuit) personal and laptop computers are now widely available, and are being increasingly used in lower-end markets as a result.

Supercomputers in particular often have highly unique architectures that differ significantly from the basic stored-program architecture and from general-purpose computers.{{efn|However, it is also very common to construct supercomputers out of many pieces of cheap commodity hardware; usually individual computers connected by networks. These so-called [[computer cluster]]s can often provide supercomputer performance at a much lower cost than customized designs. While custom architectures are still used for most of the most powerful supercomputers, there has been a proliferation of cluster computers in recent years.{{sfn|TOP500|2006|p={{page needed|date=March 2022}}}} }} They often feature thousands of CPUs, customized high-speed interconnects, and specialized computing hardware. Such designs tend to be useful for only specialized tasks due to the large scale of program organization required to use most of the available resources at once. Supercomputers usually see usage in large-scale [[Computer simulation|simulation]], [[Rendering (computer graphics)|graphics rendering]], and [[cryptography]] applications, as well as with other so-called "[[embarrassingly parallel]]" tasks.

== Software ==
{{Main|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 [[Computer hardware|hardware]] from which the system is built. Computer software includes computer programs, [[Library (computing)|libraries]] and related non-executable [[Data (computing)|data]], such as [[Software documentation|online documentation]] or [[digital media]]. It is often divided into [[system software]] and [[application software]]. Computer hardware and software require each other and neither can be realistically used on its own. When software is stored in hardware that cannot easily be modified, such as with [[BIOS]] [[Read-only memory|ROM]] in an [[IBM PC compatible]] computer, it is sometimes called "firmware".

{| class="wikitable"
|-
| rowspan="7" | [[Operating system]] /System Software
|| [[Unix]] and [[Berkeley Software Distribution|BSD]] || [[UNIX System V]], [[IBM AIX]], [[HP-UX]], [[Solaris (operating system)|Solaris]] ([[SunOS]]), [[IRIX]], [[List of BSD operating systems]]
|-
| [[Linux]] || [[List of Linux distributions]], [[Comparison of Linux distributions]]
|-
| [[Microsoft Windows]] || [[Windows 95]], [[Windows 98]], [[Windows NT]], [[Windows 2000]], [[Windows ME]], [[Windows XP]], [[Windows Vista]], [[Windows 7]], [[Windows 8]], [[Windows 8.1]], [[Windows 10]], [[Windows 11]]
|-
| [[DOS]] || [[86-DOS]] (QDOS), [[IBM PC DOS]], [[MS-DOS]], [[DR-DOS]], [[FreeDOS]]
|-
| [[Macintosh operating systems]] || [[Classic Mac OS]], [[macOS]] (previously OS X and Mac OS X)
|-
| [[Embedded operating system|Embedded]] and [[Real-time operating system|real-time]] || [[List of operating systems#Embedded|List of embedded operating systems]]
|-
| Experimental || [[Amoeba (operating system)|Amoeba]], [[Oberon (operating system)|Oberon]]–[[A2 (operating system)|AOS, Bluebottle, A2]], [[Plan 9 from Bell Labs]]
|-
| rowspan="2" | [[Library (computing)|Library]] || [[Multimedia]] || [[DirectX]], [[OpenGL]], [[OpenAL]], [[Vulkan|Vulkan (API)]]
|-
| Programming library || [[C standard library]], [[Standard Template Library]]
|-
| rowspan="2" | [[Data (computing)|Data]] || [[Protocol (computing)|Protocol]] || [[Internet protocol suite|TCP/IP]], [[Kermit (protocol)|Kermit]], [[File Transfer Protocol|FTP]], [[Hypertext Transfer Protocol|HTTP]], [[Simple Mail Transfer Protocol|SMTP]]
|-
| [[File format]] || [[HTML]], [[XML]], [[JPEG]], [[Moving Picture Experts Group|MPEG]], [[Portable Network Graphics|PNG]]
|-
| rowspan="2" | [[User interface]] || [[Graphical user interface]] ([[WIMP (computing)|WIMP]]) || [[Microsoft Windows]], [[GNOME]], [[KDE]], [[QNX]] Photon, [[Common Desktop Environment|CDE]], [[GEM (desktop environment)|GEM]], [[Aqua (user interface)|Aqua]]
|-
| [[Text-based (computing)|Text-based user interface]] || [[Command-line interface]], [[Text user interface]]
|-
| rowspan="9" | [[Application software|Application]] Software
|| [[Office suite]] || [[Word processing]], [[Desktop publishing]], [[Presentation program]], [[Database management system]], Scheduling & Time management, [[Spreadsheet]], [[Accounting software]]
|-
| Internet Access || [[Web browser|Browser]], [[Email client]], [[Web server]], [[Mail transfer agent]], [[Instant messaging]]
|-
| Design and manufacturing || [[Computer-aided design]], [[Computer-aided manufacturing]], Plant management, Robotic manufacturing, Supply chain management
|-
| [[Computer graphics|Graphics]] || [[Raster graphics editor]], [[Vector graphics editor]], [[3D computer graphics software|3D modeler]], [[Computer animation|Animation editor]], [[3D computer graphics]], [[Video editing]], [[Image processing]]
|-
| [[Digital audio|Audio]] || [[Digital audio editor]], [[Audio player (software)|Audio playback]], [[Audio mixing|Mixing]], [[Software synthesizer|Audio synthesis]], [[Computer music]]
|-
| Software engineering || [[Compiler]], [[Assembler (computer programming)|Assembler]], [[Interpreter (computing)|Interpreter]], [[Debugger]], [[Text editor]], [[Integrated development environment]], [[Software performance analysis]], [[Revision control]], [[Software configuration management]]
|-
| Educational || [[Edutainment]], [[Educational game]], [[Serious game]], [[Flight simulator]]
|-
| [[Video game|Games]] || [[Strategy game|Strategy]], [[Arcade game|Arcade]], [[Puzzle video game|Puzzle]], [[Simulation video game|Simulation]], [[First-person shooter]], [[Platform game|Platform]], [[Massively multiplayer online game|Massively multiplayer]], [[Interactive fiction]]
|-
| Misc || [[Artificial intelligence]], [[Antivirus software]], [[Malware scanner]], [[Installation (computer programs)|Installer]]/[[Package management system]]s, [[File manager]]
|}

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

<!-- ATTENTION! AUTHORS: Please do not add every programming language in existence into this table—there are vastly too many of them—and the right place for listing obscure languages is in the 'List of ...' articles referenced below. Please only add very COMMONLY and CURRENTLY used or highly historically relevant languages to the lists below or else things will rapidly spiral out of control.
-->
{| class="wikitable"
|+[[Programming language]]s
|| Lists of programming languages || [[Timeline of programming languages]], [[List of programming languages by category]], [[Generational list of programming languages]], [[List of programming languages]], [[Non-English-based programming languages]]
|-
|| Commonly used [[assembly language]]s || [[ARM architecture|ARM]], [[MIPS architecture|MIPS]], [[X86 assembly language|x86]]
|-
|| Commonly used [[high-level programming language]]s || [[Ada (programming language)|Ada]], [[BASIC]], [[C (programming language)|C]], [[C++]], [[C Sharp (programming language)|C#]], [[COBOL]], [[Fortran]], [[PL/I]], [[REXX]], [[Java (programming language)|Java]], [[Lisp (programming language)|Lisp]], [[Pascal (programming language)|Pascal]], [[Object Pascal]]
|-
|| Commonly used [[scripting language]]s || [[Bourne shell|Bourne script]], [[JavaScript]], [[Python (programming language)|Python]], [[Ruby (programming language)|Ruby]], [[PHP]], [[Perl]]
|}

=== Programs ===
The defining feature of modern computers which distinguishes them from all other machines is that they can be [[computer programming|programmed]]. That is to say that some type of [[Instruction (computer science)|instructions]] (the [[Computer program|program]]) can be given to the computer, and it will process them. Modern computers based on the [[von Neumann architecture]] often have machine code in the form of an [[imperative programming language]]. In practical terms, a computer program may be just a few instructions or extend to many millions of instructions, as do the programs for [[word processor]]s and [[web browser]]s for example. A typical modern computer can execute billions of instructions per second ([[FLOPS|gigaflops]]) and rarely makes a mistake over many years of operation. Large computer programs consisting of several million instructions may take teams of [[programmer]]s years to write, and due to the complexity of the task almost certainly contain errors.

==== Stored program architecture ====
{{Main|Computer program|Computer programming}}
[[File:SSEM Manchester museum.jpg|thumb|right|Replica of the [[Manchester Baby]], the world's first electronic [[stored-program computer]], at the [[Museum of Science and Industry (Manchester)|Museum of Science and Industry]] in Manchester, England]]
This section applies to most common [[RAM machine]]–based computers.

In most cases, computer instructions are simple: add one number to another, move some data from one location to another, send a message to some external device, etc. These instructions are read from the computer's [[Computer data storage|memory]] and are generally carried out ([[execution (computing)|executed]]) in the order they were given. However, there are usually specialized instructions to tell the computer to jump ahead or backwards to some other place in the program and to carry on executing from there. These are called "jump" instructions (or [[Branch (computer science)|branches]]). Furthermore, jump instructions may be made to happen [[conditional (programming)|conditionally]] so that different sequences of instructions may be used depending on the result of some previous calculation or some external event. Many computers directly support [[subroutine]]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 [[control flow|flow of control]] within the program and it is what allows the computer to perform tasks repeatedly without human intervention.

Comparatively, a person using a pocket [[calculator]] can perform a basic arithmetic operation such as adding two numbers with just a few button presses. But to add together all of the numbers from 1 to 1,000 would take thousands of button presses and a lot of time, with a near certainty of making a mistake. On the other hand, a computer may be programmed to do this with just a few simple instructions. The following example is written in the [[MIPS architecture|MIPS assembly language]]:
{{Clear}}
<syntaxhighlight lang="asm">
  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
</syntaxhighlight>

Once told to run this program, the computer will perform the repetitive addition task without further human intervention. It will almost never make a mistake and a modern PC can complete the task in a fraction of a second.

==== Machine code ====
In most computers, individual instructions are stored as [[machine code]] with each instruction being given a unique number (its operation code or [[opcode]] for short). The command to add two numbers together would have one opcode; the command to multiply them would have a different opcode, and so on. The simplest computers are able to perform any of a handful of different instructions; the more complex computers have several hundred to choose from, each with a unique numerical code. Since the computer's memory is able to store numbers, it can also store the instruction codes. This leads to the important fact that entire programs (which are just lists of these instructions) can be represented as lists of numbers and can themselves be manipulated inside the computer in the same way as numeric data. The fundamental concept of storing programs in the computer's memory alongside the data they operate on is the crux of the von Neumann, or stored program, architecture.<ref>{{cite book |last1=Cragon |first1=Harvey |title=Computer Architecture and Implementation |date=2000 |publisher=Cambridge University Press |isbn=978-0-521-65168-4 |page=5 |url={{GBurl|id=_ykfBAWBkxoC}} |access-date=10 June 2022 |archive-date=30 July 2022 |archive-url=https://web.archive.org/web/20220730093353/https://www.google.com/books/edition/Computer_Architecture_and_Implementation/_ykfBAWBkxoC |url-status=live }}</ref><ref>{{cite book |last1=Xu |first1=Zhiwei |last2=Zhang |first2=Jialin |title=Computational Thinking: A Perspective on Computer Science |date=2021 |publisher=Springer |location=Singapore |isbn=978-981-16-3848-0 |page=60 |url={{GBurl|id=s2RXEAAAQBAJ}} |access-date=10 June 2022 |quote=It is called the stored program architecture or stored program model, also known as the von Neumann architecture. We will use these terms interchangeably. |archive-date=30 July 2022 |archive-url=https://web.archive.org/web/20220730093353/https://www.google.com/books/edition/Computational_Thinking_A_Perspective_on/s2RXEAAAQBAJ |url-status=live }}</ref> In some cases, a computer might store some or all of its program in memory that is kept separate from the data it operates on. This is called the [[Harvard architecture]] after the [[Harvard Mark I]] computer. Modern von Neumann computers display some traits of the Harvard architecture in their designs, such as in [[CPU cache]]s.

While it is possible to write computer programs as long lists of numbers ([[machine code|machine language]]) and while this technique was used with many early computers,{{efn|Even some later computers were commonly programmed directly in machine code. Some [[minicomputer]]s like the DEC [[PDP-8]] could be programmed directly from a panel of switches. However, this method was usually used only as part of the [[booting]] process. Most modern computers boot entirely automatically by reading a boot program from some [[non-volatile memory]].}} 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&nbsp;– a [[mnemonic]] such as ADD, SUB, MULT or JUMP. These mnemonics are collectively known as a computer's [[assembly language]]. Converting programs written in assembly language into something the computer can actually understand (machine language) is usually done by a computer program called an assembler.

[[File:FortranCardPROJ039.agr.jpg|thumb|right|A 1970s [[punched card]] containing one line from a [[Fortran]] program. The card reads: "Z(1) = Y + W(1)" and is labeled "PROJ039" for identification purposes.]]

==== Programming language ====
{{Main|Programming language}}
Programming languages provide various ways of specifying programs for computers to run. Unlike [[natural language]]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]] by a [[compiler]] or an [[Assembly language#Assembler|assembler]] before being run, or translated directly at run time by an [[interpreter (computing)|interpreter]]. Sometimes programs are executed by a hybrid method of the two techniques.

===== Low-level languages =====
{{Main|Low-level programming language}}
Machine languages and the assembly languages that represent them (collectively termed ''low-level programming languages'') are generally unique to the particular architecture of a computer's central processing unit ([[CPU]]). For instance, an [[ARM architecture]] CPU (such as may be found in a [[smartphone]] or a [[handheld video game|hand-held videogame]]) cannot understand the machine language of an [[x86]] CPU that might be in a [[Personal computer|PC]].{{efn|However, there is sometimes some form of machine language compatibility between different computers. An [[x86-64]] compatible microprocessor like the AMD [[Athlon 64]] is able to run most of the same programs that an [[Intel Core 2]] microprocessor can, as well as programs designed for earlier microprocessors like the Intel [[Pentium]]s and [[Intel 80486]]. This contrasts with very early commercial computers, which were often one-of-a-kind and totally incompatible with other computers.}} 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 =====
{{Main|High-level programming language}}
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]]s that are able to express the needs of the [[programmer]] more conveniently (and thereby help reduce programmer error). High level languages are usually "compiled" into machine language (or sometimes into assembly language and then into machine language) using another computer program called a [[compiler]].{{efn|High level languages are also often [[interpreted language|interpreted]] rather than compiled. Interpreted languages are translated into machine code on the fly, while running, by another program called an [[interpreter (computing)|interpreter]].}} 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]]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.<ref name="Leach2016">{{cite book |author=Leach |first=Ronald J. |url={{GBurl|id=8W2mCwAAQBAJ}} |title=Introduction to Software Engineering |date=27 January 2016 |publisher=CRC Press |isbn=978-1-4987-0528-8 |page=11 |access-date=26 November 2022}}</ref> As problems become larger and more complex, features such as subprograms, modules, formal documentation, and new paradigms such as object-oriented programming are encountered.<ref name="Zhu2005">{{cite book |author=Zhu |first=Hong |url={{GBurl|id=rqRVbb0SKjEC}} |title=Software Design Methodology: From Principles to Architectural Styles |date=22 March 2005 |publisher=Elsevier |isbn=978-0-08-045496-2 |pages=47–72 |access-date=26 November 2022}}</ref> Large programs involving thousands of line of code and more require formal software methodologies.<ref name="Leach2016b">{{cite book |author=Leach |first=Ronald J. |url={{GBurl|id=8W2mCwAAQBAJ}} |title=Introduction to Software Engineering |date=27 January 2016 |publisher=CRC Press |isbn=978-1-4987-0528-8 |page=56 |access-date=26 November 2022}}</ref> The task of developing large [[Computer software|software]] systems presents a significant intellectual challenge.<ref name="Knight2012">{{cite book |author=Knight |first=John |url={{GBurl|id=fn06DwAAQBAJ}} |title=Fundamentals of Dependable Computing for Software Engineers |date=12 January 2012 |publisher=CRC Press |isbn=978-1-4665-1821-6 |page=186 |access-date=26 November 2022}}</ref> Producing software with an acceptably high reliability within a predictable schedule and budget has historically been difficult;<ref name="Brooks1975">{{cite book |author1=Brooks (Jr.) |first=Frederick P. |url={{GBurl|id=gWgPAQAAMAAJ}} |title=The Mythical Man-month: Essays on Software Engineering |date=1975 |publisher=Addison-Wesley Publishing Company |isbn=978-0-201-00650-6 |access-date=26 November 2022}}</ref> the academic and professional discipline of software engineering concentrates specifically on this challenge.<ref name="Sommerville2007">{{cite book |author=Sommerville |first=Ian |url={{GBurl|id=B7idKfL0H64C}} |title=Software Engineering |date=2007 |publisher=Pearson Education |isbn=978-0-321-31379-9 |pages=4–17 |access-date=26 November 2022}}</ref>

==== Bugs ====
{{Main|Software bug}}
[[File:First Computer Bug, 1945.jpg|thumb|The actual first computer bug, a moth found trapped on a relay of the [[Harvard Mark II]] computer]]
Errors in computer programs are called "[[Software bug|bugs]]". They may be benign and not affect the usefulness of the program, or have only subtle effects. However, in some cases they may cause the program or the entire system to "[[Hang (computing)|hang]]", becoming unresponsive to input such as [[Computer mouse|mouse]] clicks or keystrokes, to completely fail, or to [[Crash (computing)|crash]].<ref>{{Cite web |title=Why do computers crash? |url=https://www.scientificamerican.com/article/why-do-computers-crash/ |access-date=2022-03-03 |website=Scientific American |language=en |archive-date=1 May 2018 |archive-url=https://web.archive.org/web/20180501093613/https://www.scientificamerican.com/article/why-do-computers-crash/ |url-status=live }}</ref> Otherwise benign bugs may sometimes be harnessed for malicious intent by an unscrupulous user writing an [[Exploit (computer security)|exploit]], code designed to take advantage of a bug and disrupt a computer's proper execution. Bugs are usually not the fault of the computer. Since computers merely execute the instructions they are given, bugs are nearly always the result of programmer error or an oversight made in the program's design.{{efn|It is not universally true that bugs are solely due to programmer oversight. Computer hardware may fail or may itself have a fundamental problem that produces unexpected results in certain situations. For instance, the [[Pentium FDIV bug]] caused some [[Intel Corporation|Intel]] microprocessors in the early 1990s to produce inaccurate results for certain [[floating point]] division operations. This was caused by a flaw in the [[microprocessor]] design and resulted in a partial recall of the affected devices.}} Admiral [[Grace Hopper]], an American computer scientist and developer of the first [[compiler]], is credited for having first used the term "bugs" in computing after a dead moth was found shorting a relay in the [[Harvard Mark II]] computer in September 1947.<ref name="taylor84">{{cite magazine
|first=Alexander L. III
|last=Taylor
|url=http://www.time.com/time/printout/0,8816,954266,00.html
|archive-url=https://web.archive.org/web/20070316082637/http://www.time.com/time/printout/0,8816,954266,00.html

|archive-date=16 March 2007
|title=The Wizard Inside the Machine
|magazine=[[Time (magazine)|Time]]
|date=16 April 1984
|access-date =17 February 2007}}</ref>

== Networking and the Internet ==
{{Main|Computer network{{!}}Computer networking|Internet}}
[[File:Internet map 1024.jpg|thumb|left|Visualization of a portion of the [[Routing|routes]] on the Internet]]
Computers have been used to coordinate information between multiple physical locations since the 1950s. The U.S. military's [[Semi-Automatic Ground Environment|SAGE]] system was the first large-scale example of such a system, which led to a number of special-purpose commercial systems such as [[Sabre (computer system)|Sabre]].<ref>{{Cite book |author=Hughes |first=Agatha C. |title=Systems, Experts, and Computers |publisher=[[MIT Press]] |year=2000 |isbn=978-0-262-08285-3 |page=161 |quote=The experience of SAGE helped make possible the first truly large-scale commercial real-time network: the SABRE computerized airline reservations system.}}</ref>

In the 1970s, computer engineers at research institutions throughout the United States began to link their computers together using telecommunications technology. The effort was funded by ARPA (now [[DARPA]]), and the [[computer network]] that resulted was called the [[ARPANET]].<ref>{{cite arXiv|title=A Brief History of the Internet|last1=Leiner|first1=Barry M. |last2=Cerf|first2=Vinton G. |last3=Clark|first3=David D. |last4=Kahn|first4=Robert E. |last5=Kleinrock|first5=Leonard |last6=Lynch|first6=Daniel C. |last7=Postel|first7=Jon |last8=Roberts|first8=Larry G. |last9=Wolf|first9=Stephen |year=1999|eprint=cs/9901011}}<!-- Additional cite journal parameters: |bibcode=1999cs........1011L |url=http://www.isoc.org/internet/history/brief.shtml|publisher=[[Internet Society]]|access-date=20 September 2008|url-status=dead --></ref> 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 computers. 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, computer networking become almost ubiquitous, due to the spread of applications like e-mail and the [[World Wide Web]], combined with the development of cheap, fast networking technologies like [[Ethernet]] and [[Asymmetric digital subscriber line|ADSL]].

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.
{{Clear}}

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

=== Computer architecture paradigms ===
There are many types of [[computer architecture]]s:
* [[Quantum computer]] vs. [[Chemical computer]]
* [[Scalar processor]] vs. [[Vector processor]]
* [[Non-Uniform Memory Access]] (NUMA) computers
* [[Register machine]] vs. [[Stack machine]]
* [[Harvard architecture]] vs. [[von Neumann architecture]]
* [[Cellular architecture]]

Of all these [[abstract machine]]s, a quantum computer holds the most promise for revolutionizing computing.<ref>{{cite book |last1=Dumas II |first1=Joseph D. |url={{GBurl|id=ZWaUurOwMPQC|q=quantum%20computers}} |title=Computer Architecture: Fundamentals and Principles of Computer Design |date=2005 |publisher=CRC Press |isbn=978-0-8493-2749-0 |page=340 |language=en |access-date=9 November 2020}}</ref> [[Logic gate]]s are a common abstraction which can apply to most of the above [[Digital data|digital]] or [[analog signal|analog]] paradigms. The ability to store and execute lists of instructions called [[Computer program|programs]] makes computers extremely versatile, distinguishing them from [[calculator]]s. The [[Church–Turing thesis]] is a mathematical statement of this versatility: any computer with a [[Turing-complete|minimum capability (being Turing-complete)]] is, in principle, capable of performing the same tasks that any other computer can perform. Therefore, any type of computer ([[netbook]], [[supercomputer]], [[cellular automaton]], etc.) is able to perform the same computational tasks, given enough time and storage capacity.

=== Artificial intelligence ===
In the 20th century, [[artificial intelligence]] systems were predominantly [[Symbolic artificial intelligence|symbolic]]: they executed code that was explicitly programmed by software developers.<ref>{{Cite web |title=A Gentle Introduction to Symbolic AI |url=https://www.kdnuggets.com/gentle-introduction-symbolic-ai |access-date=2025-05-17 |website=KDnuggets |language=en-US}}</ref> [[Machine learning]] models, however, have a set parameters that are adjusted throughout training, so that the model learns to accomplish a task based on the provided data. The efficiency of machine learning (and in particular of [[Neural network (machine learning)|neural networks]]) has rapidly improved with progress in hardware for [[parallel computing]], mainly [[Graphics processing unit|graphics processing units]] (GPUs).<ref>{{Cite news |date=2023-05-25 |title=Nvidia: The chip maker that became an AI superpower |url=https://www.bbc.com/news/business-65675027 |access-date=2025-05-17 |work=BBC |language=en-GB}}</ref> Some [[Large language model|large language models]] are able to control computers or robots.<ref>{{Cite web |last=Jindal |first=Siddharth |date=2024-10-22 |title=Anthropic's Claude 3.5 Now Controls Your Computer Like You Do |url=https://analyticsindiamag.com/ai-news-updates/anthropics-claude-3-5-now-controls-your-computer-like-you-do/ |access-date=2025-05-17 |website=Analytics India Magazine |language=en-US}}</ref><ref>{{Cite web |last=Edwards |first=Benj |date=2025-02-20 |title=Microsoft’s new AI agent can control software and robots |url=https://arstechnica.com/ai/2025/02/microsofts-new-ai-agent-can-control-software-and-robots/ |access-date=2025-05-17 |website=Ars Technica |language=en}}</ref> AI progress may lead to the creation of [[artificial general intelligence]] (AGI), a type of AI that could accomplish virtually any intellectual task at least as well as humans.<ref>{{Cite web |last= |first= |date=2025-04-03 |title=The Definition of Artificial General Intelligence (AGI) |url=https://time.com/collections/the-ai-dictionary-from-allbusiness-com/7273928/definition-of-artificial-general-intelligence-agi/ |access-date=2025-05-17 |website=TIME |language=en}}</ref>

== Professions and organizations ==
As the use of computers has spread throughout society, there are an increasing number of careers involving computers.
{| class="wikitable"
|+[[:Category:Computer occupations|Computer-related professions]]
|-
| Hardware-related || [[Electrical engineering]], [[Electronic engineering]], [[Computer engineering]], [[Telecommunications engineering]], [[Optical engineering]], [[Nanoengineering]]
|-
| Software-related || [[Computer science]], [[Computer engineering]], [[Desktop publishing]], [[Human–computer interaction]], Information technology, [[Information systems (discipline)|Information systems]], [[Computational science]], Software engineering, [[Video game industry]], [[Web design]]
|}

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

{| class="wikitable"
|+[[:Category:Information technology organizations|Organizations]]
| Standards groups || [[American National Standards Institute|ANSI]], [[International Electrotechnical Commission|IEC]], [[Institute of Electrical and Electronics Engineers|IEEE]], [[Internet Engineering Task Force|IETF]], [[International Organization for Standardization|ISO]], [[World Wide Web Consortium|W3C]]
|-
| Professional societies || [[Association for Computing Machinery|ACM]], [[Association for Information Systems|AIS]], [[Institution of Engineering and Technology|IET]], [[International Federation for Information Processing|IFIP]], [[British Computer Society|BCS]]
|-
| [[Free software|Free]]/[[open source software]] groups || [[Free Software Foundation]], [[Mozilla Foundation]], [[Apache Software Foundation]]
|}

== See also ==
{{Div col|colwidth=18em}}
* [[Computability theory]]
* [[Computer security]]
* [[Glossary of computer hardware terms]]
* [[History of computer science]]
* [[List of computer term etymologies]]
* [[List of computer system manufacturers]]
* [[List of fictional computers]]
* [[List of films about computers]]
* [[List of pioneers in computer science]]
* [[Outline of computers]]
* [[Pulse computation]]
* [[TOP500]] (list of most powerful computers)
* [[Unconventional computing]]
{{div col end}}

== Notes ==
{{notelist}}

== References ==
{{Reflist|30em}}

== Sources ==
{{Refbegin|30em}}
* {{cite book |first=B. V. |last=Bowden |title=Faster than thought |year=1953 |publisher=Pitman publishing corporation |location=New York, Toronto, London |ref=BOWDEN }}
* {{cite book |ref=BERK |last=Berkeley |first=Edmund |year=1949 |title=Giant Brains, or Machines That Think |url=https://archive.org/details/in.ernet.dli.2015.285568 |publisher=John Wiley & Sons }}
* {{cite book |last=Bromley |first=Allan G. |contribution=Difference and Analytical Engines |title=Computing Before Computers |editor-first=William |editor-last=Aspray |publisher=Iowa State University Press |location=Ames |pages=59–98 |url=http://ed-thelen.org/comp-hist/CBC-Ch-02.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://ed-thelen.org/comp-hist/CBC-Ch-02.pdf |archive-date=2022-10-09 |url-status=live |date=1990 |isbn=978-0-8138-0047-9}}
* {{cite journal |ref=AIKEN |last=Cohen |first=Bernard |year=2000 |title=Howard Aiken, Portrait of a computer pioneer |journal=Physics Today |volume=53 |issue=3 |pages=74–75 |publisher=The MIT Press |location=Cambridge, Massachusetts|isbn=978-0-262-53179-5 |bibcode=2000PhT....53c..74C |doi=10.1063/1.883007 |doi-access=free}}
* {{cite book|last=Collier|first=Bruce|title=The little engine that could've: The calculating machines of Charles Babbage|year=1970|publisher=Garland Publishing|isbn=978-0-8240-0043-1|url=http://robroy.dyndns.info/collier/index.html|ref=COLLIER|access-date=24 October 2013|archive-date=20 January 2007|archive-url=https://web.archive.org/web/20070120190231/http://robroy.dyndns.info/collier/index.html|url-status=live}}
* {{cite book |ref=COUFFIGNAL |last=Couffignal |first=Louis |year=1933 |title=Les machines à calculer; leurs principes, leur évolution |publisher=Gauthier-Villars |location=Paris }}
* {{Cite book |ref=DEC |author=Digital Equipment Corporation |publisher=Digital Equipment Corporation |location=[[Maynard, Massachusetts|Maynard, MA]] |title=PDP-11/40 Processor Handbook |url=https://www.minttwist.com/wp-content/uploads/2016/06/D-09-30-PDP11-40-Processor-Handbook.pdf |year=1972 |author-link=Digital Equipment Corporation |access-date=27 November 2017 |archive-date=1 December 2017 |archive-url=https://web.archive.org/web/20171201030856/https://www.minttwist.com/wp-content/uploads/2016/06/D-09-30-PDP11-40-Processor-Handbook.pdf |url-status=live }}
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* {{cite book |ref=JACWEB |last=Essinger |first=James |year=2004 |title=Jacquard's Web, How a hand loom led to the birth of the information age |publisher=Oxford University Press |isbn=978-0-19-280577-5 |url-access=registration |url=https://archive.org/details/jacquardswebhowh0000essi }}
* {{Cite book|last=Evans|first=Claire L.|title=Broad Band: The Untold Story of the Women Who Made the Internet|publisher=Portfolio/Penguin|year=2018|isbn=978-0-7352-1175-9|location=New York|url={{GBurl|id=C8ouDwAAQBAJ|q=9780735211759|pg=PP1}}|access-date=9 November 2020}}
* {{cite book |ref=FELT |last=Felt |first=Dorr E. |title=Mechanical arithmetic, or The history of the counting machine |publisher=Washington Institute |location=Chicago |year=1916 |url=https://archive.org/details/mechanicalarithm00feltrich }}
* {{cite book |ref=IFRAH |last=Ifrah |first=Georges |year=2001 |title=The Universal History of Computing: From the Abacus to the Quantum Computer |location=New York |publisher=John Wiley & Sons |isbn=978-0-471-39671-0 |url=https://archive.org/details/unset0000unse_w3q2 }}
* {{Cite book|last=Lavington |first=Simon |title=A History of Manchester Computers |year=1998 |edition=2nd |publisher=The British Computer Society |location=Swindon |isbn=978-0-902505-01-8 }}
* {{cite book |ref=LIGO |last=Ligonnière |first=Robert |year=1987 |title=Préhistoire et Histoire des ordinateurs |publisher=Robert Laffont |location=Paris |isbn=978-2-221-05261-7 }}
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* {{cite web |ref={{harvid|TOP500|2006}} |url=http://www.top500.org/lists/2006/11/overtime/Architectures |title=Architectures Share Over Time |access-date=27 November 2006 |last=Meuer |first=Hans |author-link=Hans Meuer |author2=Strohmaier, Erich |author3=Simon, Horst |author4=Dongarra, Jack |author4-link=Jack Dongarra |date=13 November 2006 |publisher=[[TOP500]] |archive-date=20 February 2007 |archive-url=https://web.archive.org/web/20070220095222/http://www.top500.org/lists/2006/11/overtime/Architectures }}
* {{cite book |first=Maboth |last=Moseley |title=Irascible Genius, Charles Babbage, inventor |year=1964 |publisher=Hutchinson |location=London |ref=GENIUS }}
* {{cite web |url=http://www.cs.ncl.ac.uk/publications/articles/papers/398.pdf |title=From Analytical Engine to Electronic Digital Computer: The Contributions of Ludgate, Torres, and Bush |last1=Randell |first1=Brian |author-link1=Brian Randell |year=1982 |access-date=29 October 2013  |archive-url=https://web.archive.org/web/20130921055055/http://www.cs.ncl.ac.uk/publications/articles/papers/398.pdf |archive-date=21 September 2013}}
* {{cite journal |last=Schmandt-Besserat |first=Denise |author-link=Denise Schmandt-Besserat |date=1999 |title=Tokens: The Cognitive Significance |journal=Documenta Praehistorica |volume=XXVI |url=http://www.laits.utexas.edu/ghazal/Chap1/dsb/chapter1.html  |archive-url=https://web.archive.org/web/20120130084757/http://www.laits.utexas.edu/ghazal/Chap1/dsb/chapter1.html |archive-date=30 January 2012 }}
* {{Cite journal |last=Schmandt-Besserat |first=Denise |author-link=Denise Schmandt-Besserat |year=1981 |title=Decipherment of the earliest tablets |journal=Science |volume=211 |issue=4479 |pages=283–285 |doi=10.1126/science.211.4479.283 |pmid=17748027 |bibcode=1981Sci...211..283S}}
* {{Cite journal|last=Smith|first=Erika E.|date=2013|title=Recognizing a Collective Inheritance through the History of Women in Computing|journal=CLCWeb: Comparative Literature and Culture|volume=15|issue=1|pages=1–9 |doi=10.7771/1481-4374.1972|doi-access=free}}
* {{Cite conference |last1=Verma |first1=G. |last2=Mielke |first2=N. |title=Reliability performance of ETOX based flash memories |conference=IEEE International Reliability Physics Symposium |year=1988 }}
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{{Refend}}

== External links ==
* {{commons category-inline|Computers}}
* {{sister-inline
|project=v
|links=[[v:How things work college course/Computer quiz|Wikiversity has a quiz on this article]]
|short=yes}}

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{{Basic computer components}}
{{digital systems}}
{{Mainframes}}
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[[Category:Computers| ]]
[[Category:Consumer electronics]]
[[Category:Articles containing video clips]]
[[Category:Articles with example code]]
[[Category:Electronics industry]]