英语翻译

thefirstgenerationofcomputers,whichusedvacuumtubes,cameoutinthelate1940s.univacIisanexampleofthesecomputerswhichcouldperformthousandsofcalculationspersecond.in1960,thesecondgenerationofcomputerswasdevelopandthesecouldperformworktentimesfasterthantheirpredecessor.thereasonforthisextraspeedwastheuseoftransistorsinsteadofvacuumtubesthesecond-generationcomputersweresmaller,fasterandmoredependablethanfirst-generationcomputers.thethird-generationcomputersappearedonthemarketin1965.thesecomputerscoulddoamillioncalculationsasecond,whichis1000timesasmanyasfirst-generationcomputers.unlikesecond-generationcomputers,thesearecontrolledbytinyintegrated

circuitsandareconsequentlysmallerandmoredependable.fourth-generationcomputershavenow

arrived,andtheintegratedcircuitsthatarebeingdevelopedhavebeengreatlyreducedinsize.

thisisduetomicrominiaturization,whichmeansthatthecircuitsaremuchsmallerthanbefore；as

manyas1000tinycircuitsnowfitontoasinglechip.achipisasquareortectangularpieceofsilicon,usuallyfrom1/10to1/4inch,uponwhichserverallayersofanintegratedcircuitareetchedorimprinted,afterwhichthecircuitisencapsulatedinplastic,ceramicormetal.fourth-generationcomputersare50timesfasterthanthird-generationcomputersandcancompleteapproximately1000000instructionspersecond.