Background
Intheearlyinformationprocessingsystem,thecomputeronlyservedoneuser.Althoughbatchprocessingcaneffectivelyimprovetheutilizationrateofthemachine,theuserlosestheabilitytocontrolandmodifythejobafterhandingoverthejobtothesystem,anditusuallytakesseveralhoursorevendaystogetthedesiredresult.Usershopetodirectlyenjoycomputerresourcesthroughtheirownterminals,sotheideaoftimesharingappears.Duetothehighspeedofthecomputer,itcanservemultipleusersefficientlyonthebasisoftimesharing.
Systemintroduction
Thetime-sharingprocessingsystemisacomputersystem(seefigure),whichincludesmanyindependent,relativelylow-speedonlineterminaldevicesthatcanbeusedatthesametime(seeonlineprocessing),eachterminalcandirectlyaccessthecentralprocessingunit.Thecentralprocessingunitiscontrolledbyaclockandswitchesfromoneterminaltoanotheraccordingtoacertaintime.Itcompletesapartofeachjobwithinthespecifiedtimeslice,savestheresultoftheintermediateprocessing,andthenturnstoanotherterminal,andsoonuntilthejobisallover.Thetimesliceassignedtoeachuserisveryshort,forexample,about1/40second,butduetothehighspeedofthecomputer,itcanstillcompletealotofoperationprocessingduringthistime.Switchingbetweenusersisextremelyfrequent,whichcanmakeusersfeelasiftheyareusinganinformationprocessingsystemalone.Usersoperateindependentlyofeachotherwithoutconfusionordestruction.Generally,acertainprioritycanalsobegiventothejobsofeachuser,andthejobsarearrangedinaqueueaccordingtothepriority.Jobswithhigherprioritymaygetmoreorlongertimeslices.
Providingservices
Thetime-sharingsystemisdifferentfromthosedesignedforthespecialpurposeofadepartment.Itstrivestoprovideservicesformultipledepartmentsandhandleawiderrangeofbusinessandscience.Operation.Therefore,itsmainmemoryhasalargecapacityandthecentralprocessingunithasgoodversatilitytosupportallcomplexprogrammingandcontrolfunctions.Time-sharingprocessinghasalargenumberofusers'informationstoredinthesamefilesystem,soconfidentialityismoreimportant,andnecessarymeasuresneedtobetaken(seedatasecurity).
Systemuse
Time-sharingprocessingisthebasicmethodofcommercialcomputingservices.Commercialcomputingcompaniessellprocessingtimetoalltypesofcustomersandprovideavarietyofservices,sothatcustomersonlyneedtocareabouttheapplicationsystemstheyhavebuilt,withouthavingtoconsiderissuessuchasdatabasemanagementanddatacommunication.Customerscanconnecttothecomputersystemthrougharemoteterminalandpayaccordingtothetimetheterminalisconnectedtothecentralprocessingunitandthetimeoccupiedbythecentralprocessingunit.Variousschoolscanusethetime-sharingprocesstoprovidestudentswithopportunitiestogetonthecomputer.Commercialandindustrialsectorsalsoneedinformationprocessingsystemswithtime-sharingcapabilitiesintheirdailywork.
Thedesignofthesingle-chiptime-sharingsystem
Thesingle-chipsystemisoftenanembeddedcontrolsystem,somostofthecurrentsingle-chipsystemsarestillreal-timesystems.Thedesignideasofthetime-sharingsystemareoftenthosemulti-channelrepetitivedetectioncontrolsystemsthatcantrulyembodythedesignideasofthetime-sharingsystem.Eveninthesemulti-channelrepetitivedetectioncontrolsystems,itsreal-timeperformanceisveryimportant.Inotherwords,thetime-sharingsystemdesignideaisappliedinthesingle-chipmicrocomputersystem,butitstimelinessshouldbeconsideredfirst.
Withtheimprovementoftheperformanceofthesingle-chipmicrocomputer,thesoftwareizationofsomehardwarefunctionsinthesystemdesignofthesingle-chipmicrocomputerisageneraltrend.Butatthesametime,therapidchiptechnologyalsoprovidesthepossibilityforlow-costhardwaretocompletehigh-performancefunctions.Whetherafunctionisrealizedbyhardwareorsoftwarecannotbegeneralized.Itisthegoalofeverysingle-chipsystemdesignertoachievethehighestcost-performanceratiooftheentiresystemthroughsystemdesign.
Inthehardwaredesignofthesingle-chiptime-sharingsystem,thetimelinessrequirementsofthesystemcannotbereduced,andtheprocessingspeedofmostsingle-chipcomputersisrelativelyslow.Therefore,inthedesignoftheinterfacehardware,somedevicesthatcanholdtheamountofinformation,suchasflip-flopsandlatches,shouldbeused.Atthesametime,itisrequiredthatthesedevicesshouldbetri-stategateoutput,becauseitisamulti-channeltime-sharingsystem.WhentheCPUisnotaccessed,thedeviceoutputpresentsahighimpedancetofacilitatethebus'saccesstootherdevices.Also,sometime-consumingoperationswithsoftwareshouldbetransferredtohardwareforcompletion.SuchasLEDdynamicdisplay,thereisnoneedtouseintel?8155orintel?8255hardwareinterfacesothatthesoftwarealwaystakesgreatpainstodisplaynumbers.Itcanbedonewithintel?8279orMAX7218andMAX7219programmableperipheraldevices,sothatthedisplayisbothbeautifulandbeautiful.simple.Ofcourse,whichfunctionsarelefttothehardwaretocomplete,andwhichfunctionsarelefttothesoftwaretocomplete,shouldbespecificallydesignedaccordingtodifferentsystems.Inshort,theoverallconsiderationshouldbegiventothepursuitofthehighestprice-performanceratio.