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OperatingSystems

OPERATING SYSTEMS:

Lesson 1:Introduction to Operating Systems

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Jesús Carretero PérezDavid Expósito Singh José Daniel García SánchezFrancisco Javier García BlasFlorin Isaila

OperatingSystems

WhystudyOperatingSystems?

a) OS,anditsinternals,largelyinfluencesgeneralfunctioning,includingsecurityandperformance.

b) ImportanceofOSchoiceinanorganizationishigherandhigher.Trendtostrategicdecision.

c) Knowledgefundamentaltodevelopapplicationsifgoodperformanceisdesiredandtounderstandcausesofmanyproblems.

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OperatingSystems

UnderstandingOS

• WhichOStakesbetteradvantageofagivensystemcapabilities?

• DoestheOSsupportallthedevicesIintendtoconnecttothecomputer?Ifnot,whatcanIdo?

• Isitsecureenoughfortheenvironmentitwillbeintegratedin?

• Willmyapplicationsrun«smoothly»onthechosenOS?Howwillmyconcreteworkloadadapttotheplatform?

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OperatingSystems

Tomaketherightchoice

• IsiteasytofindadminsforthisOS?Isadministrationanobscure taskneedingultra-specializedpersonnel?

• WhatsupportdoestheOShave?Whichistheupdatepublishingrate?

• Besidescost,whatfutureexpectationsdoesithave?

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Protect your investment

OperatingSystems

Todevelopsoftwarewithgoodperformance

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• SoftwareneedsOSservicesformaytasks.– WhatservicesdoestheOSofferandhowdoIinvokethem?

• Totakeadvantageofnewarchitecturesmultithreadingisessential.– HowdoIdevelopamultithreadedapplicationformyOS?

OperatingSystems

Anengineermustbe

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OPERATING SYSTEMAGNOSTIC

OperatingSystems

FourComponentsofaComputerSystem

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OperatingSystems

ComputerSystemStructure

• Computersystemcanbedividedintofourcomponents– Hardware– providesbasiccomputingresources

• CPU,memory,I/Odevices– Operatingsystem

• Controlsandcoordinatesuseofhardwareamongvariousapplicationsandusers

– Applicationprograms– definethewaysinwhichthesystemresourcesareusedtosolvethecomputingproblemsoftheusers• Wordprocessors,compilers,webbrowsers,databasesystems,videogames

– Users• People,machines,othercomputers

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OperatingSystems

ComputerSystemOrganization

• Computer-systemoperation– OneormoreCPUs,devicecontrollersconnectthroughcommonbus

providingaccesstosharedmemory– ConcurrentexecutionofCPUsanddevicescompetingformemory

cycles

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OperatingSystems

HowaModernComputerWorks

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OperatingSystems

Computer-SystemOperation

• I/OdevicesandtheCPUcanexecuteconcurrently• Eachdevicecontrollerisinchargeofaparticulardevicetype

• Eachdevicecontrollerhasalocalbuffer• CPUmovesdatafrom/tomainmemoryto/fromlocalbuffers

• I/Oisfromthedevicetolocalbufferofcontroller• DevicecontrollerinformsCPUthatithasfinisheditsoperationbycausinganinterrupt

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OperatingSystems

InterruptTimeline

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OperatingSystems

CommonFunctionsofInterrupts

• Interrupttransferscontroltotheinterruptserviceroutinegenerally,throughtheinterrupt vector,whichcontainstheaddressesofalltheserviceroutines

• Interruptarchitecturemustsavetheaddressoftheinterruptedinstruction

• Incominginterruptsaredisabled whileanotherinterruptisbeingprocessedtopreventalostinterrupt

• Atrap isasoftware-generatedinterruptcausedeitherbyanerrororauserrequest

• Anoperatingsystemisinterruptdriven

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OperatingSystems

InterruptHandling

• TheoperatingsystempreservestheCPUstatebystoringregistersandtheprogramcounter

• Determineswhichtypeofinterrupthasoccurred.• Separatesegmentsofcodedeterminewhatactionshouldbetakenforeachtypeofinterrupt

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OperatingSystems

I/OStructure

• AfterI/Ostarts,controlreturnstouserprogramonlyuponI/Ocompletion– AtmostoneI/Orequestisoutstandingatatime,nosimultaneousI/Oprocessing

• Systemcall– requesttotheoperatingsystemtoallowusertowaitforI/Ocompletion

• Device-statustablecontainsentryforeachI/Odeviceindicatingitstype,address,andstate

• OperatingsystemindexesintoI/Odevicetabletodeterminedevicestatusandtomodifytableentrytoincludeinterrupt

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OperatingSystems

DirectMemoryAccessStructure

• Usedforhigh-speedI/Odevicesabletotransmitinformationatclosetomemoryspeeds

• DevicecontrollertransfersblocksofdatafrombufferstoragedirectlytomainmemorywithoutCPUintervention

• Onlyoneinterruptisgeneratedperblock,ratherthantheoneinterruptperbyte

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OperatingSystems

Storage-DeviceHierarchy

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OperatingSystems

PerformanceofVariousLevelsofStorage

• Movementbetweenlevelsofstoragehierarchycanbeexplicitorimplicit

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OperatingSystems

MigrationofIntegerAfromDisktoRegister

• Multitaskingenvironmentsmustbecarefultousemostrecentvalue,nomatterwhereitisstoredinthestoragehierarchy

• MultiprocessorenvironmentmustprovidecachecoherencyinhardwaresuchthatallCPUshavethemostrecentvalueintheircache

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OperatingSystems

StorageStructure

• Mainmemory– onlylargestoragemediathattheCPUcanaccessdirectly

• Secondarystorage– extensionofmainmemorythatprovideslargenonvolatilestoragecapacity

• Magneticdisks– rigidmetalorglassplatterscoveredwithmagneticrecordingmaterial– Disksurfaceislogicallydividedintotracks,whicharesubdividedintosectors

– Thediskcontrollerdeterminesthelogicalinteractionbetweenthedeviceandthecomputer

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OperatingSystems

StorageHierarchy

• Storagesystemsorganizedinhierarchy– Speed– Cost– Volatility

• Caching – copyinginformationintofasterstoragesystem;mainmemorycanbeviewedasalastcacheforsecondarystorage

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OperatingSystems

Caching

• Importantprinciple,performedatmanylevelsinacomputer(inhardware,operatingsystem,software)

• Informationinusecopiedfromslowertofasterstoragetemporarily

• Fasterstorage(cache)checkedfirsttodetermineifinformationisthere– Ifitis,informationuseddirectlyfromthecache(fast)– Ifnot,datacopiedtocacheandusedthere

• Cachesmallerthanstoragebeingcached– Cachemanagementimportantdesignproblem– Cachesizeandreplacementpolicy

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OperatingSystems

WhatisanOperatingSystem?

• Aprogramthatactsasanintermediarybetweenauserofacomputerandthecomputerhardware

• Operatingsystemgoals:– Executeuserprogramsandmakesolvinguserproblemseasier

– Makethecomputersystemconvenienttouse– Usethecomputerhardwareinanefficientmanner

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OperatingSystems

OperatingSystemDefinition

• OSisaresourceallocator– Managesallresources– Decidesbetweenconflictingrequestsforefficientandfairresourceuse

• OSisacontrolprogram– Controlsexecutionofprogramstopreventerrorsandimproperuseofthecomputer

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OperatingSystems

OperatingSystemDefinition(Cont)

• Nouniversallyaccepteddefinition• “Everythingavendorshipswhenyouorderanoperatingsystem” isgoodapproximation– Butvarieswildly

• “Theoneprogramrunningatalltimesonthecomputer” isthekernel.Everythingelseiseitherasystemprogram(shipswiththeoperatingsystem)oranapplicationprogram

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OperatingSystems

OperatingSystemStructure

• Multiprogramming neededforefficiency– SingleprogramcannotkeepCPUandI/Odevicesbusyatalltimes– Multiprogramming organizes jobs(codeanddata)soCPUalwayshasoneto

execute– Asubsetoftotaljobs insystemiskeptinmemory– Onejobselectedandrunviajobscheduling– Whenithastowait(for I/Oforexample),OSswitchestoanother job

• Timesharing(multitasking)islogicalextensioninwhichCPUswitchesjobssofrequently thatuserscaninteractwitheachjobwhileitisrunning, creatinginteractive computing– Responsetime shouldbe<1second– Eachuserhasatleastoneprogramexecutinginmemory[process– Ifseveraljobs readytorunatthesametime[ CPUscheduling– Ifprocessesdon’t fitinmemory,swappingmovestheminandouttorun– Virtualmemoryallowsexecutionofprocessesnotcompletely inmemory

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OperatingSystems

Responsetime

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OperatingSystems

MemoryLayoutforMultiprogrammedSystem

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OperatingSystems

Operating-SystemOperations

• Interruptdrivenbyhardware• Softwareerrororrequestcreatesexceptionortrap

– Divisionbyzero,requestforoperatingsystemservice• Otherprocessproblemsincludeinfiniteloop,processes

modifyingeachotherortheoperatingsystem• Dual-modeoperationallowsOStoprotectitselfand

othersystemcomponents– Usermodeandkernelmode– Modebitprovidedbyhardware

• Providesabilitytodistinguishwhensystemisrunningusercodeorkernelcode

• Someinstructionsdesignatedasprivileged,onlyexecutable inkernelmode

• Systemcallchangesmodetokernel,returnfromcallresets ittouser

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OperatingSystems

TransitionfromUsertoKernelMode

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OperatingSystems

Process Management

• Aprocessisaprograminexecution.Itisaunitofworkwithinthesystem.Programisapassiveentity,processisanactiveentity.

• Processneedsresourcestoaccomplishitstask– CPU,memory,I/O,files– Initializationdata

• Processterminationrequiresreclaimofanyreusableresources• Single-threadedprocesshasoneprogramcounterspecifyinglocationof

nextinstructiontoexecute– Processexecutesinstructionssequentially,oneatatime,until

completion• Multi-threadedprocesshasoneprogramcounterperthread• Typicallyasystemhasmanyprocesses,someusers,someoperating

systemrunningconcurrentlyononeormoreCPUs– ConcurrencybymultiplexingtheCPUsamongtheprocesses/threads

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OperatingSystems

ProcessManagementActivities

Theoperatingsystemisresponsibleforthefollowingactivitiesinconnectionwithprocessmanagement:

• Creatinganddeletingbothuserandsystemprocesses

• Suspendingandresumingprocesses• Providingmechanismsforprocesssynchronization• Providingmechanismsforprocesscommunication• Providingmechanismsfordeadlockhandling

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OperatingSystems

MemoryManagement

• Alldatainmemorybeforeandafterprocessing• Allinstructionsinmemoryinordertoexecute• Memorymanagementactivities

– Keepingtrackofwhichpartsofmemoryarecurrentlybeingusedandbywhom

– Decidingwhichprocesses(orpartsthereof)anddatatomoveintoandoutofmemory

– Allocatinganddeallocatingmemoryspaceasneeded

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OperatingSystems

StorageManagement

• OSprovidesuniform,logicalviewofinformationstorage– Abstractsphysicalpropertiestologicalstorageunit- file– Eachmediumiscontrolledbydevice(i.e.,diskdrive,tape

drive)• Varyingpropertiesincludeaccessspeed,capacity,data-transferrate,accessmethod(sequentialorrandom)

• File-Systemmanagement– Filesusuallyorganizedintodirectories– Accesscontrolonmostsystemstodeterminewhocan

accesswhat– OSactivitiesinclude

• Creatinganddeletingfilesanddirectories• Primitivestomanipulatefilesanddirs• Mappingfilesontosecondarystorage• Backupfilesontostable(non-volatile)storagemedia

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OperatingSystems

Mass-StorageManagement

• Usually disks used to store data that does not fit in main memory or data that must be kept for a “long” period of time

• Proper management is of central importance• Entire speed of computer operation hinges on disk subsystem and

its algorithms• OS activities

– Free-space management– Storage allocation– Disk scheduling

• Some storage need not be fast– Tertiary storage includes optical storage, magnetic tape– Still must be managed– Varies between WORM (write-once, read-many-times) and RW

(read-write)

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OperatingSystems

I/OSubsystem

• OnepurposeofOSistohidepeculiaritiesofhardwaredevicesfromtheuser

• I/Osubsystemresponsiblefor– MemorymanagementofI/Oincludingbuffering(storingdatatemporarilywhileitisbeingtransferred),caching(storingpartsofdatainfasterstorageforperformance),spooling(theoverlappingofoutputofonejobwithinputofotherjobs)

– Generaldevice-driverinterface– Driversforspecifichardwaredevices

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OperatingSystems

ProtectionandSecurity

• Protection– anymechanismforcontrollingaccessofprocessesoruserstoresourcesdefinedbytheOS

• Security– defenseofthesystemagainstinternalandexternalattacks– Hugerange,includingdenial-of-service,worms,viruses,identity

theft,theftofservice• Systemsgenerallyfirstdistinguishamongusers,todeterminewho

candowhat– Useridentities(userIDs,securityIDs)includenameandassociated

number,oneperuser– UserIDthenassociatedwithallfiles,processesofthatuserto

determineaccesscontrol– Groupidentifier(groupID)allowssetofuserstobedefinedand

controlsmanaged,thenalsoassociatedwitheachprocess,file– PrivilegeescalationallowsusertochangetoeffectiveIDwithmore

rights

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OperatingSystems

Conceptualstructure

• Executionmodes:– Usermode:Executesuserprocesses.– Kernelmode:ExecutestheOSkernel.

• ProcessesandOSuseseparatememoryspaces.

• WhenaprocessneedsaservicerequestsittotheOSthroughasystemcall.– TheOperatingSystementersexecutiontoperformrequestedfunction.

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OperatingSystems

Structure

OperatingSystems

Monolitics

Structured

Layered

Client/Server

Modular

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OperatingSystems

MonoliticOS

• Noclearorwelldefinedstructure.• AlltheOScodelinkedintoasingleexecutablerunningin

kernelmode.– Singleaddressspace.– Nodatahidingamongmodules.

• Moreefficientatthecostofverycomplexdevelopmentandmaintenance.

• Examples:– AllOSuntil’80,includingUNIX.– MS-DOSandcurrentUNIXvariants:Solaris,Linux,AIX,HP-UX,...

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OperatingSystems

LayeredOS

• Organizationasasetoflayerswithclearandwelldefinedinterfaces.• Eachlayerontopoflowerlayer.• Advantates:

– Modularity.– Datahiding.– Betterdevelopmentanddebugging.

• Lessefficientduetoneedtocrossmanylayerstoperformanoperation.• DifficulttodistributeOSfunctionsintolayers.• Examples:

– MacOS Xkernel– OS/2

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OperatingSystems

Client/Serverapproach

¨ Mostservicesasuserprocesseswithasmallamountoffunctioality intoamicrokernel.

¨ Advantages:¨ Veryflexible. Eachservercanbedevelopedanddebuggedinisolation.¨ Easilyextensible toadistributedmodel

¨ Drawbacks:¤ Overheadinservicesexecution.

¨ Examples:¤ MinixyAmoeba(Tanenbaum)¤ MacOSandWindowsNT.

¤ Howeverservicesexecuted inkernelspaceforperformancereasons.

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OperatingSystems

Modular

• Most modern operating systems implement kernel moduleso Uses object-oriented approacho Each core component is separateo Each talks to the others over known interfaceso Each is loadable as needed within the kernel

• Overall, similar to layers but with more flexible

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OperatingSystems

Classifications

¨Numberofprocesses:¤Single-Task.¤Multitaks.

¨InteractionMode:¤Interactive.¤Batch.

¨Numberofusers:¤Monouser.¤Multiuser.

¨Numberofprocessors:¤Monoprocessor.¤Multiprocessor.

¨Threading:¤Monothread.¤Multithread.

¨uses:¤Client.¤Server.¤Embedded.¤Real-Time.

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OperatingSystems

OSstartup

• OSstartsupwhecomputerisswitchedon.– Initiallyinsecondarystorage.– Howdoesitcometomainmemory?– Howdesitstartexecutionafterbeingloaded?

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OperatingSystems

Phases

ROMBoot

OS Loader

OS resident

partNormal

execution

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OperatingSystems

Computer Startup

• bootstrapprogram isloadedatpower-uporreboot– TypicallystoredinROMorEPROM,generallyknownas

firmware– Initializesallaspectsofsystem– Loadsoperatingsystemkernelandstartsexecution

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OperatingSystems

ROMboot

• RESETsignalloadspredefinedvaluesinregisters.– PC:bootaddressinroomboot.

• StartrunningROMboot:– Systemhardwaretest.– LoadintomemorytoOSloader.

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OperatingSystems

OSloader

¨Programloaderisindiskbootsector.

¨ResponsibleforloadingtherestoftheOS.

¨Verifiesthemagicwordinbootsector.

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OperatingSystems

GeneratingtheOS

• OSdesignedforacompleteclassofmachineswithseveralvariantsofconfigurationsandmanysupporteddevices.

• NeedtogenerateOScopybasedoncharacteristicsofspecificmachineconfiguration.

• Generationperformedduringinitialinstallation.

GenericOS

SpecificOSGeneration

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OperatingSystems

OPERATING SYSTEMS:

Lesson 1:Introduction to Operating Systems

51

Jesús Carretero PérezDavid Expósito Singh José Daniel García SánchezFrancisco Javier García BlasFlorin Isaila