Acomputerisamachinethatmanipulatesdataaccordingtoalistofinstructions.

　　Thefirstdevicesthatresemblemoderncomputersdatetothemid-20thcentury(1940–1945),althoughthecomputerconceptandvariousmachinessimilartocomputersexistedearlier.Earlyelectroniccomputerswerethesizeofalargeroom,consumingasmuchpowerasseveralhundredmodernpersonalcomputers.Moderncomputersarebasedontinyintegratedcircuitsandaremillionstobillionsoftimesmorecapablewhileoccupyingafractionofthespace.Today,simplecomputersmaybemadesmallenoughtofitintoawristwatchandbepoweredfromawatchbattery.Personalcomputers,invariousforms,areiconsoftheInformationAgeandarewhatmostpeoplethinkofas"acomputer";however,themostcommonformofcomputerinusetodayistheembeddedcomputer.Embeddedcomputersaresmall,simpledevicesthatareusedtocontrolotherdevices—forexample,theymaybefoundinmachinesrangingfromfighteraircrafttoindustrialrobots,digitalcameras,andchildren'stoys.

　　Theabilitytostoreandexecutelistsofinstructionscalledprogramsmakescomputersextremelyversatileanddistinguishesthemfromcalculators.TheChurch–Turingthesisisamathematicalstatementofthisversatility:anycomputerwithacertainminimumcapabilityis,inprinciple,capableofperformingthesametasksthatanyothercomputercanperform.Therefore,computerswithcapabilityandcomplexityrangingfromthatofapersonaldigitalassistanttoasupercomputerareallabletoperformthesamecomputationaltasksgivenenoughtimeandstoragecapacity.

　　Historyofcomputing

　　Mainarticle:Historyofcomputerhardware

　　TheJacquardloomwasoneofthefirstprogrammabledevices.Itisdifficulttoidentifyanyonedeviceastheearliestcomputer,partlybecausetheterm"computer"hasbeensubjecttovaryinginterpretationsovertime.Originally,theterm"computer"referredtoapersonwhoperformednumericalcalculations(ahumancomputer),oftenwiththeaidofamechanicalcalculatingdevice.

　　Thehistoryofthemoderncomputerbeginswithtwoseparatetechnologies-thatofautomatedcalculationandthatofprogrammability.

　　Examplesofearlymechanicalcalculatingdevicesincludedtheabacus,theslideruleandarguablytheastrolabeandtheAntikytheramechanism(whichdatesfromabout150-100BC).HeroofAlexandria(c.10–70AD)builtamechanicaltheaterwhichperformedaplaylasting10minutesandwasoperatedbyacomplexsystemofropesanddrumsthatmightbeconsideredtobeameansofdecidingwhichpartsofthemechanismperformedwhichactionsandwhen.Thisistheessenceofprogrammability.

　　The"castleclock",anastronomicalclockinventedbyAl-Jazariin1206,isconsideredtobetheearliestprogrammableanalogcomputer.Itdisplayedthezodiac,thesolarandlunarorbits,acrescentmoon-shapedpointertravellingacrossagatewaycausingautomaticdoorstoopeneveryhour,andfiveroboticmusicianswhoplaymusicwhenstruckbyleversoperatedbyacamshaftattachedtoawaterwheel.Thelengthofdayandnightcouldbere-programmedeverydayinordertoaccountforthechanginglengthsofdayandnightthroughouttheyear.

　　TheendoftheMiddleAgessaware-invigorationofEuropeanmathematicsandengineering,andWilhelmSchickard's1623devicewasthefirstofanumberofmechanicalcalculator