CITS2002SystemsProgramming

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AnIntroductiontoOperatingSystemsWhatisanoperatingsystem?

Apieceofsystemssoftwarethatprovidesaconvenient,efficientenvironmentfortheexecutionofuserprograms.

It'sprobablythelargestandmostcomplexprogramyou'lleverrun!

Whydoweneedanoperatingsystem?

Theuser'sviewpoint:toprovidetheuserinterface,commandinterpreter,anddirectorystructure,andtoexecuteapplicationprograms(wordprocessor,emailclient,webbrowser,MP3player).

Theprogrammingenvironmentviewpoint:toenhancethebaremachine,toprovideutilityprograms(suchascompilers,editors,filters),toprovidehigh-levelinputandoutput(I/O),tostructureinformationintofiles,andtoimproveaccesstomemory(size,protection,sharing).

Theefficiencyviewpoint:toreplacethe(longdeparted)humanoperator,toscheduletasks,toefficientlystoreandretrievedata,andtoinvokeandshareprograms.

Theeconomicviewpoint:toallowsimultaneoususeandschedulingofresources,includingdisk-bounddataandexpensiveperipherals.

Traditionally,wewouldsummarizeanoperatingsystem'sgoalsasmaking"thesystem"convenienttouseandschedulingitsresourcesefficientlyandfairly.

Inaddition,itmustsupporthardwareandsoftwarenotyetdeveloped.

CITS2002SystemsProgramming,Lecture3,p1,2ndAugust2021.

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OperatingSystem≠User/ComputerInterfaceAnoperatingsystemisoftensimplyseenanddescribedastheuser/computerinterface.

Weoften(mistakenly)claimtounderstand,andlikeordislike,an"operatingsystem"basedonitsinterface.

Suchaninterfaceprovidesuswith:

programcreation(editors,compilers,debuggers,linkers)programexecution(characterandgraphical)accesstoI/Odevices(bothfixedandremovable)constrainedaccesstofilesofmediaconstrainedaccessto"internal"resourceserrordetection,response,reporting,andaccountingandmonitoring.

Whetherornotacertaininterfacerunsonaparticularhardwareoroperatingsystemplatformisusuallydictatedbyeconomics,marketing,andpolitics-nottechnology.

CITS2002SystemsProgramming,Lecture3,p2,2ndAugust2021.

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OperatingSystem≡ResourceManagerAnoperatingsystemisbetterconsideredasbeingincontrolofitshardwareandsoftwareresources.

Betterstill,becausethe"controls"areoftentemporalorexternaltotheoperatingsystemitself,let'sconsidertheoperatingsystemasaresourcemanager.

Anoperatingsystemisjustanotherprogramrunningontheavailablehardware.

Mostofthetime,theoperatingsystemrelinquishescontroltotheuserprocessesuntilthehardwareagaindispatchesthecontrol.

CITS2002SystemsProgramming,Lecture3,p3,2ndAugust2021.

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OperatingSystemsMustBeExtensibleOfimportanceisanoperatingsystem'sabilitytoevolvetomeetnewhardwareandsoftwaredemands:

Newhardwareisconstantlyintroduced-addingmorememorypresentslittledifficulty;newtypesofdisks,videocards,etc,aremoreproblematic.Newapplicationprograms,tools,andsystemservicesareadded.Fixesandpatchesarereleasedtocorrectoperatingsystemdeficiencies.

Allofthissuggeststhattheoperatingsystem,asaprogram,needstobeextensible-amodulardesignseemsessential.Considerthefollowingfigure:

Aviewofoperatingsystemservices

Ofcourse,theabovediagramprovidesaverysimplifiedrepresentationofoperatingsystemsandtheirservices.Inpractice,therelationshipsbetweenthemodularcomponentsbecomeverycomplex-LinuxandWindows-10.

CITS2002SystemsProgramming,Lecture3,p4,2ndAugust2021.

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TraditionalOperatingSystemServices

CPUscheduling:distributeorapportioncomputingtimeamongseveralprocesses(ortasks)whichappeartoexecutesimultaneously.

Memorymanagement:divideandsharephysicalmemoryamongseveralprocesses.

Swapping:moveprocessesandtheirdatabetweenmainmemoryanddisktopresenttheillusionofabiggermachine.

I/Odevicesupport:providespecializedcodetooptimallysupportdevicerequirements.

Filesystem:organizemassstorage(ondisk)intofilesanddirectories.

CITS2002SystemsProgramming,Lecture3,p5,2ndAugust2021.

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TraditionalOperatingSystemServices,continued

Utilityprograms:accounting,setting/constrainingsystemresourceaccess,manipulatingthefilesystem.

Acommandinterface:textualorgraphical,toenableinteractiveinterrogationandmanipulationofoperatingsystemfeatures.

Systemcalls:allowconstrainedaccesstotheinterioroftherunningoperatingsystem(asaprogram).

Protection:keepprocessesfrominterferingwitheachother,theirdata,and"thesystem",whilstpermittingsharingwhenrequested.

Communication:allowusersandprocessestocommunicatewithinasinglemachine(inter-processcommunication),andacrossnetworks.

CITS2002SystemsProgramming,Lecture3,p6,2ndAugust2021.

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AWhirlwindHistoryofOperatingSystemsTounderstandthewaymodernoperatingsystemsarethewaytheyare,itisusefultoexaminetheirevolutionoverthelastsixtyyearsorso.

Advancesinoperatingsystemsoftenaccompaniedadvancesinhardware,fallingprices,and"exploding"capacities.

ThefirsttruedigitalcomputerwasdesignedbyEnglishmathematicianCharlesBabbage(1792-1871).

AlthoughBabbagespentmostofhisworkinglifeandfortunebuildinghis"analyticalengine",itsmechanicaldesignandthewoodentechnologyofthedaycouldnotprovidetherequiredprecision.

Needlesstosay,theanalyticalenginedidnothaveanoperatingsystem.

CITS2002SystemsProgramming,Lecture3,p7,2ndAugust2021.

Everythingthatcanbeinventedhasbeeninvented.— CharlesH.Duell,Commissioner,U.S.OfficeofPatents,1899.“

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1945-55:VacuumTubesandPlugboardsUntilWorldWarII,littleprogresswasmadeinconstructingdigitalcomputers.Sixsignificantgroupscanreasonablyclaimthefirstelectricalcomputers:

TommyFlowersandMaxNewman,BletchleyPark,England,HowardAitken,Harvard,JohnvonNeumann,InstituteofAdvanceStudies,Princeton,TomKilburnandFreddieWilliams,Manchester,J.P.EckertandW.Mauchley,UniversityofPennsylvania,andKonranZuse,Germany.

Asinglegroupofpeopledesigned,built,programmed,operatedandmaintainedeachmachine.Althoughfillingsmallwarehouses,withtensofthousandsofvacuumtubes,theywerenomatchfortoday'scheapesthomecomputers.

Programswereloadedmanuallyusingconsoleswitches,ormorelikelybydirectreconfigurationofwiring;indicationofaprogram'sexecutionanddebuggingreturnedthroughconsolelights.

Advantages:Interactive,anduserreceivedimmediateresponse.

Disadvantages:Expensivemachinewasidlemostofthetime,becausepeople'sreactions(andthinking)wereslow.Programminganddebuggingweretedious;hardwarewasveryunreliable.Eachprogramwasselfcontained,includingitsowncodeformathematicalfunctionsandI/Odevicesupport.

CITS2002SystemsProgramming,Lecture3,p8,2ndAugust2021.

Ithinkthereisaworldmarketformaybefivecomputers.— ThomasWatson(1874-1956),ChairmanofIBM,1943.“

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1955-65:TransistorsandBatchSystemsProgramminglanguagesandoperatingsystems(asweknowthemtoday)stillunheardof.Collectionsofsubroutines(procedures)todriveperipheralsandtoevaluatetrigonometricfunctionswerethefirstexamplesofoperatingsystemsservices.Themid-1950ssawtheuser(stillastheprogrammer)submittingadeckofpunchedHollerithcardsdescribingajobtobeexecuted.

Giventhehighcostofcomputers,waystoincreasetheirutilitywerequicklysought.Thegeneralsolutionwasthebatchsystem.

Similar/relatedprograms,perhapseachrequiringtheFORTRAN(FORmulaTRANslation)compiler,orasetofmathematicalroutines,werebatchedtogethersothattherequiredroutinesneedonlybephysicallyloadedonce.

Programswerefirstwrittenonpapertape,intheemergingFORTRANlanguageorinassemblylanguage,andthencopiedtopunchedcards.Suchdecksofcardsincludedjobcontrolcards,theprogramitself,andoftentheprogram'sdata.

Jobssubmittedbydifferentusersweresequencedautomaticallybytheoperatingsystem'sresidentmonitor.Earlyperipherals,suchaslargemagnetictapedrives,wereusedtobatchinput(jobsanddata)andspool(fromSimultaneousPeripheralOperationOnLine)output.

CITS2002SystemsProgramming,Lecture3,p9,2ndAugust2021.

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1955-65:TransistorsandBatchSystems,continuedGenerally,aninexpensivecomputer,suchasanIBM1401,wasusedforreadingcardsandprintingfromoutputtapes.Theexpensivemachine,suchasanIBM7094,wasusedsolelyforthemathematicalcomputations.

Advantages:

The(true,computational)computerwaskeptbusier.

Disadvantages:

Thecomputerwasnolongerinteractive.Jobsexperiencedalongerturnaroundtime.TheCPUwasstillidlemuchofthetimeforjobs.Otherjobsremainedqueuedforexecution.

Thesignificantoperatingsysteminnovationatthistimewastheintroductionofacommandinterpreter(ajobcontrollanguage-JCL)todescribe,order,andcommenceexecutionofjobs.

Theresidentmonitorwasalsoprotectedfromtheuserprograms,andmanagedtheautomatedloadingoftheprogramsafterthemonitor.

CITS2002SystemsProgramming,Lecture3,p10,2ndAugust2021.

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1965-1980:IntegratedCircuitsandMultiprogrammingIntheearly1960s,computermanufacturerstypicallymadetwotypesofcomputers-word-oriented,largescalescientificcomputers(suchastheIBM-7094),andcharacter-orientedcommercialcomputers(suchastheIBM-1401),whichwerereallybettersuitedforI/O.

Incompatibilityandalackofanupgradepathweretheproblemsoftheday.

IBMattemptedtoaddressbothproblemswiththereleaseoftheirSystem/360,afamilyofsoftwarecompatiblemachinesdifferingonlyincapacity,priceandperformance.Themachineshadthesamearchitectureandinstructionset.

WithheavyCPU-boundscientificcalculations,I/Oisinfrequent,sothetimespent(wasted)waitingwasnotsignificant.However,commercialprocessingprogramsintheemergingCOBOL(ComputerOrientedBusinessOrganizationalLanguage)oftenspent80-90%ofitstimewaitingforI/Otocomplete.

TheadventofseparateI/OprocessorsmadesimultaneousI/OandCPUexecutionpossible.

TheCPUwasmultiplexed(shared),oremployedmultiprogramming,amongstanumberofjobs-whileonejobwaswaitingforI/OfromcomparativelyslowI/Odevices(suchasakeyboardortape),anotherjobcouldusetheCPU.

JobswouldrununtiltheircompletionoruntiltheymadeanI/Orequest.

Advantages:

Interactivitywasrestored.TheCPUwaskeptbusyifenoughjobswerereadytorun.

Disadvantages:

Thecomputerhardwareandtheoperatingsystemsoftwarebecamesignificantlymorecomplex(andtherehasbeennolookingbacksince!).

CITS2002SystemsProgramming,Lecture3,p11,2ndAugust2021.

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1965-1980:IntegratedCircuitsandMultiprogramming,continuedStill,thedesireforquickerresponsetimesinspiredavariantofmultiprogramminginwhicheachusercommunicateddirectlywithoneofamultitudeofI/Odevices.

Theintroductionoftimesharingintroducedpre-emptivescheduling.Jobswouldexecuteforatmostpre-definedtimeinterval,afterwhichitwasanotherjob'sturntousetheCPU.

Thefirstserioustimesharingsystem(CTSS,fromMIT1962)lackedadequatememoryprotection.

Most(modern)operatingsystemcomplexitywasfirstintroducedwiththesupportofmultiprogramming-schedulingalgorithms,deadlockprevention,memoryprotection,andmemorymanagement.

Theworld'sfirstcommerciallyavailabletime-sharingcomputer,theDECPDP-6,wasinstalledinUWA'sPhysicsBuildingin1965-cf.Cyberhistory,byKeithFalloon,UWAMScthesis,2001,andpdp6-serials.

CITS2002SystemsProgramming,Lecture3,p12,2ndAugust2021.

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EarlyOperatingSystemSecurity

Veryearlyoperatingsystems,onone-user-at-a-timecomputersystems,assistedtheusertoloadtheirprogramsandcommencetheirexecution.

Therewaslittletoprotectand,ifanerrantprogrammodifiedtheexecutiveprogram,thenonlythecurrentuserwasaffected.Asmoreofacourtesy,theexecutivemightclearmemorysegmentsandcheckitselfbeforeacceptingthenextprogram.

Asmulti-taskingoperatingsystemsemerged,accountabilityofresourceusebecamenecessary,andoperatingsystemmonitorsoversawtheexecutionofprograms.

Aswithmodernoperatingsystems,therewastheneedto:

protecttheoperatingsystemfromtheprogram,protectprogramsfromthemselves,protectprogramsfromeachother,andconstraindataaccesstothecorrectprogram(s).

Untilsystemresourcesbecamemoreplentiful(andcheaper)attemptsweremadetomaximizeresourcesharing-securitywasaconsequent,notaninitial,goal.

e.g.processschedulingpoliciesweredominatedbyalreadyrunningprocessesrequestingresources(suchaslibrariesandtapes)thatwerealreadyinuse.

Atthislevel,computersecurityismoreconcernedwithreliabilityandcorrectness,thanaboutdeliberateattacksonprograms,data,andthesystem.

CITS2002SystemsProgramming,Lecture3,p13,2ndAugust2021.

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1970s:MinicomputersandMicrocomputers

Anothermajordevelopmentoccurringinparallelwasthephenomenalgrowthinminicomputers,startingwiththeDEC(DigitalEquipmentCorporation)PDP-1(ProgrammedDataProcessor)in1961.ThePDP-1,with4Kof18-bitwordscostonlyUS$120,000-5%oftheIBM7094.

Thetrendwastowardsmanysmallmid-rangepersonalcomputers,ratherthanasinglemainframe.

Earlyminicomputersandmicrocomputersweresimpleintheirhardwarearchitectures,andsotherewassomeregressiontoearlieroperatingsystemideas(singleuser,nopre-emption,nomultiprogramming).

Forexample,MS-DOSonanIBM-PC(circa.1975)wasessentiallyintroducedasabatchsystem,similartothoseofthe1960s,withafewmodernadditions,suchasahierarchicalfilesystem.

Withsomenotableexceptions,thetrendquicklymovedtowardssupportofallmodernoperatingsystemfacilitiesonmicrocomputers.

Perhapsmostsignificanthasbeentheevolution,andimportance,ofoperatingsystems'userinterfaces.

Inparticular,thegraphicaldesktopmetaphorhasremainedforsometime.

CITS2002SystemsProgramming,Lecture3,p14,2ndAugust2021.

ThereareonlytwothingstocomeoutofBerkeley,UnixandLSD,andIdon'tthinkthisisacoincidence.— JeremyS.Anderson.

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Thereisnoreasonanyonewouldwantacomputerintheirhome.— KenOlsen,DECFounderandChairman,1977.“

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1980-90s:PersonalComputersandNetworking

Thedecentralizationofcomputingresources,nowdataandnotthehardware,requiredmoresupportforinter-operatingsystemcommunication-bothphysicalsupportandapplicationprogramsupport.

Asminicomputersshrunkinsize,butexplodedincapacity,thepowerfulcomputerworkstationwasborn.CompaniessuchasSunMicrosystems(SUN)andSiliconGraphics(SGI)rodethiswaveofsuccess.

Local-areanetworks(primarilyEthernetandtoken-ring)connectedworkstations,whilewide-areanetworksconnectedminicomputers.

Operatingsystemdevelopmentsincludedthedevelopmentoffastandefficientnetworkcommunicationprotocols,dataencryption(ofnetworksandfilesystems),security,reliability,andconsistencyofdistributeddata.

CITS2002SystemsProgramming,Lecture3,p15,2ndAugust2021.

640Koughttobeenoughforanybody.— BillGates(1955-),in1981.“

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2000sandBeyond:Speeds,Capacities,Mobility,andUbiquityThedesktopmetaphorforcomputerinterfacesbecomesonlyaninstanceofthewiderwebmetaphor.

Hardwarepricesdrop,andcapacitiesexplode.-42YearsofMicroprocessorTrendData-AmazingFactsandFiguresAbouttheEvolutionofHardDiskDrives-FlashBecomesCheaperthanHDDby2026

Highspeed,longdistancecommunicationlinksencouragegraphicalandaudiocommunication(surpassingtext).-TVandVideoWillTripleAverageHomeMonthlyInternetUsagetoBeyond1TBBy2025

Computersbecomeportableandincreasinglyubiquitous.-IntheFightforYourHearts,TabletsandDesktopsLosetoLaptops-DesktopvsMobilevsTabletMarketShareWorldwide

AsCPUperformancenolongerkeepspacewithMoore'sLaw,andcomputingbecomesincreasinglymobile,focusshiftstobatterylifeandmetricsofperformance/Watt.-PerformanceperWattIstheNewMoore'sLaw-WhatIsThePowerConsumptionOfDesktopComputers?

CITS2002SystemsProgramming,Lecture3,p16,2ndAugust2021.

Foryears,wethoughtthatamillionmonkeyssittingatamillionkeyboardswouldproducethecompleteworksofShakespeare.Today,thankstotheInternet,weknowthat'snottrue.— Anon.

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