BOOK2-Unit3Computers-“黄冈杯”一等奖

相关信息(FurtherInformation)

Computer

Computerisadevicethatprocessesinformationwithastonishingspeedandaccuracy．Computersprocessinformationbyhelpingtocreateitandbydisplayingit，storingit，reorganizingit，calculatingwithit，andcommunicatingittoothercomputers．Computerscanprocessnumbers，words，stillpictures，movingpictures，andsounds．Themostpowerfulcomputerscanperformtensofbillionsofcalculationspersecond．

Thecomputerhaschangedthewaywework，learn，communicate，andplay.Virtuallyeverykindoforganizationthroughouttheworldconductsbusinesswithcomputers．Students，teachers，andresearchscientistsusethecomputerasalearningtool．MillionsofindividualsandorganizationscommunicatewithoneanotheroveranetworkofcomputerscalledtheInternet．Computergamesentertainpeopleofallages．

Almostallcomputersareelectronicdigitalcomputers．Theyareelectronicintheiruseofelectriccurrent(aflowofelectriccharge)tocarryinformation．Theyaredigitalinthattheyprocessinformationasunitsofelectricchargerepresentingnumbers．Theworddigitalmeanshavingtodowithnumbers．Toenableacomputertoprocessinformationthatisnotnumerical—suchaswords，pictures，orsounds—thecomputerorsomeotherdevicemustfirstdigitizethatinformation．Adevicedigitizesinformationbytranslatingitintochargesthatrepresentnumbers．Afterthecomputerprocessesthedigitizedinformationbyworkingwiththecharges，thecomputeroradeviceconnectedtothecomputertranslatesitsresultsbackintotheiroriginalform．

Thus，anartistmightuseamachinecalledascannertodigitizeaphotograph．Theartistwouldnextprocesstheresultingelectricchargesinacomputertochangethephotograph—perhapstoaddaborder．Theartistwouldthenuseaprinterconnectedtothecomputertoproduceacopyofthealteredphoto．

Thetechnologyofcomputerhardware(thephysicalpartsofcomputersystems)hasadvancedtremendouslysince1946，whenthefirstelectronicdigitalcomputerwasbuilt．Thatmachinefilledahugeroom．Today，asinglemicroprocessor，adevicethesizeofafingernail，candothesameworkasthatpioneeringmachine．

Thetechnologyofsoftware(programs，orsetsofcomputerinstructionsandinformation)isalsoadvancingrapidly．Earlyusersofcomputerswrotetheirownsoftware．Today，mostusersbuyprogramscreatedbycompaniesthatspecializeinwritingsoftware．Hundredsofthousandsofdifferentprogramsareavailableforbusinessesandindividuals．

Becauseofadvancesinhardwareandsoftware，thepriceofcomputinghasdroppedsharply．Asaresult，thenumberofcomputersinoperationhasrisenrapidlyeversincethefirstcommercialdigitalcomputersweremanufacturedinthe1950’S．Morethan10000computerswereinoperationworldwideby1961．Tenyearslater，thenumberexceeded100000．By1990，about100millioncomputerswererunning．Bythemid-1990’s，thenumberhadreachedabout200million．

Kindsofcomputers

Computersvarywidelyinsize，speed，andability．Theymaybegroupedintofourcategories：(1)personalcomputers，(2)mainframes，(3)dedicatedcomputers，and(4)embeddedcomputers．

Personalcomputersareusedbyonepersonatatime．Thelargestpersonalcomputers，orPC’s，canfitonadesktop．Someofthesemachineshavemorethanonemicroprocessor．Besidestheprimaryprocessor，whichisageneral-purposedevice，aPCmayhaveoneormoreco-processorstohandlespecialkindsofwork．Somemachines，forexample，havemathco-processors．Othershavegraphicsco-processorstohelpprocessphotographsandotherillustrations．Stillothershavesoundco—processors．

Largeandmiddle-sizedbusinessescommonlyusePC’sinclient-servernetworks．Anetworkconsistsofagroupofcomputersconnectedbytelephonelinesorothercommunicationscables．Inaclient—servernetwork，apowerfulcentralcomputerdistributesinformationtoanumberofPC’s．Thecentralcomputeriscalledtheserver．ThePC’saretheclientsbutareusuallyreferredtoasworkstationsorsimplyPC’s．ThecentralcomputermaybeaPC，amachinemuchlikeaPCwithextra-largestoragecapacity，oranevenlargertypeofcomputer．

Theserveralsostoresallthenetwork’sessentialinformation．Inatypicalnetwork，individualsoperatingtheworkstationsobtaincopiesofinformationfromtheserver．Theworkersprocessthisinformation，thensendcopiesoftheprocessedinformationbacktotheserver．Inmostcases，theworkersareinthesameofficeastheserver．Butalargecompanymayhaveanetworkthatconnectsitsbranchofficestothemainoffice．Inaddition，manyemployeesworkoncomputersathomeandsendtheirprocesseddatatothecompanyserver．Thisuseofcomputersisknownastelecommuting．

OfficeworkersalsousePC’sthatarenotconnectedtoanetwork．Thesemachinesareusedforsuchtasksaswordprocessing，performingfinancialcalculations，andorganizingandsortingbodiesofinformationcalleddatabases．Homeusersofcomputersdosomeofthesamekindsofworkonpersonaldata．Theyuseword-processingprogramsforprivatecorrespondence，financialsoftwareforhouseholdbudgets，anddatabasemanagementprogramsforaddresslistsandrecipes．IndividualsalsousetheirhomecomputerstoplaygamesandtocommunicateovertheInternet．

Small，portablePC’sarepopularwithpeoplewhooftenworkawayfromtheirdesks．Theportablesincludelaptopcomputers，whichcanbeheldonthelap；notebookcomputers，whichareaboutthesizeofaloose-leafnotebook；