APS审核操作系统.docx

APS审核操作系统.docx

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APS审核操作系统

操作系统

OperatingSystem

WhatisanOperatingSystem?

Aprogramthatactsasanintermediarybetweenauserofacomputerandthecomputerhardware

Operatingsystemgoals:

Executeuserprogramsandmakesolvinguserproblemseasier

Makethecomputersystemconvenienttouse

Usethecomputerhardwareinanefficientmanner

ComputerSystemStructure

Computersystemcanbedividedintofourcomponents

Hardware–providesbasiccomputingresources

CPU,memory,I/Odevices

Operatingsystem

Controlsandcoordinatesuseofhardwareamongvariousapplicationsandusers

Applicationprograms–definethewaysinwhichthesystemresourcesareusedtosolvethecomputingproblemsoftheusers

Wordprocessors,compilers,webbrowsers,databasesystems,videogames

Users

People,machines,othercomputers

OperatingSystemDefinition

OSisaresourceallocator

Managesallresources

Decidesbetweenconflictingrequestsforefficientandfairresourceuse

OSisacontrolprogram

Controlsexecutionofprogramstopreventerrorsandimproperuseofthecomputer

Nouniversallyaccepteddefinition

“Theoneprogramrunningatalltimesonthecomputer”isthekernel.

Everythingelseiseitherasystemprogram（shipswiththeoperatingsystem）oranapplicationprogram

ComputerSystemOrganization

Computer-SystemArchitecture

Mostsystemsuseasinglegeneral-purposeprocessor（PDAsthroughmainframes）

Mostsystemshavespecial-purposeprocessorsaswell

Multiprocessorssystemsgrowinginuseandimportance

Alsoknownasparallelsystems,tightly-coupledsystems

Advantagesinclude

1.Increasedthroughput

2.Economyofscale

3.Increasedreliability–gracefuldegradationorfaulttolerance

Twotypes

1.AsymmetricMultiprocessing

2.SymmetricMultiprocessing

Operating-SystemOperations

Interruptdrivenbyhardware

Softwareerrororrequestcreatesexceptionortrap

Divisionbyzero,requestforoperatingsystemservice

Otherprocessproblemsincludeinfiniteloop,processesmodifyingeachotherortheoperatingsystem

Dual-modeoperationallowsOStoprotectitselfandothersystemcomponents

Usermodeandkernelmode

Modebitprovidedbyhardware

Providesabilitytodistinguishwhensystemisrunningusercodeorkernelcode

Someinstructionsdesignatedasprivileged,onlyexecutableinkernelmode

Systemcallchangesmodetokernel,returnfromcallresetsittouser

ProcessManagement

Aprocessisaprograminexecution.Itisaunitofworkwithinthesystem.Programisapassiveentity,processisanactiveentity.

Processneedsresourcestoaccomplishitstask

CPU,memory,I/O,files

Initializationdata

Processterminationrequiresreclaimofanyreusableresources

Single-threadedprocesshasoneprogramcounterspecifyinglocationofnextinstructiontoexecute

Processexecutesinstructionssequentially,oneatatime,untilcompletion

Multi-threadedprocesshasoneprogramcounterperthread

Typicallysystemhasmanyprocesses,someuser,someoperatingsystemrunningconcurrentlyononeormoreCPUs

ConcurrencybymultiplexingtheCPUsamongtheprocesses/threads

ProcessManagementActivities

Theoperatingsystemisresponsibleforthefollowingactivitiesin connectionwithprocessmanagement:

Creatinganddeletingbothuserandsystemprocesses

Suspendingandresumingprocesses

Providingmechanismsforprocesssynchronization

Providingmechanismsforprocesscommunication

Providingmechanismsfordeadlockhandling

MemoryManagement

Alldatainmemorybeforeandafterprocessing

Allinstructionsinmemoryinordertoexecute

Memorymanagementdetermineswhatisinmemorywhen

OptimizingCPUutilizationandcomputerresponsetousers

Memorymanagementactivities

Keepingtrackofwhichpartsofmemoryarecurrentlybeingusedandbywhom

Decidingwhichprocesses（orpartsthereof）anddatatomoveintoandoutofmemory

Allocatinganddeallocatingmemoryspaceasneeded

StorageManagement

OSprovidesuniform,logicalviewofinformationstorage

Abstractsphysicalpropertiestologicalstorageunit -file

Eachmediumiscontrolledbydevice（i.e.,diskdrive,tapedrive）

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

File-Systemmanagement

Filesusuallyorganizedintodirectories

Accesscontrolonmostsystemstodeterminewhocanaccesswhat

OSactivitiesinclude

Creatinganddeletingfilesanddirectories

Primitivestomanipulatefilesanddirs

Mappingfilesontosecondarystorage

Backupfilesontostable（non-volatile）storagemedia

Mass-StorageManagement

Usuallydisksusedtostoredatathatdoesnotfitinmainmemoryordatathatmustbekeptfora“long”periodoftime

Propermanagementisofcentralimportance

Entirespeedofcomputeroperationhingesondisksubsystemanditsalgorithms

OSactivities

Free-spacemanagement

Storageallocation

Diskscheduling

Somestorageneednotbefast

Tertiarystorageincludesopticalstorage,magnetictape

Stillmustbemanaged

VariesbetweenWORM（write-once,read-many-times）andRW（read-write）

I/OSubsystem

OnepurposeofOSistohidepeculiaritiesofhardwaredevicesfromtheuser

I/Osubsystemresponsiblefor

MemorymanagementofI/Oincluding

buffering（storingdatatemporarilywhileitisbeingtransferred）,

caching（storingpartsofdatainfasterstorageforperformance）,

spooling（theoverlappingofoutputofonejobwithinputofotherjobs）

Generaldevice-driverinterface

Driversforspecifichardwaredevices

AViewofOperatingSystemServices

Onesetofoperating-systemservicesprovidesfunctionsthatarehelpfultotheuser:

Userinterface-Almostalloperatingsystemshaveauserinterface（UI）

VariesbetweenCommand-Line（CLI）,GraphicsUserInterface（GUI）,Batch

Programexecution-Thesystemmustbeabletoloadaprogramintomemoryandtorunthatprogram,endexecution,eithernormallyorabnormally（indicatingerror）

I/Ooperations- ArunningprogrammayrequireI/O,whichmayinvolveafileoranI/Odevice

File-systemmanipulation- Thefilesystemisofparticularinterest.Programsneedtoreadandwritefilesanddirectories,createanddeletethem,searchthem,listfileInformation,permissionmanagement.

Communications–Processesmayexchangeinformation,onthesamecomputerorbetweencomputersoveranetwork

Communicationsmaybeviasharedmemoryorthroughmessagepassing（packetsmovedbytheOS）

Errordetection–OSneedstobeconstantlyawareofpossibleerrors

MayoccurintheCPUandmemoryhardware,inI/Odevices,inuserprogram

Foreachtypeoferror,OSshouldtaketheappropriateactiontoensurecorrectandconsistentcomputing

Debuggingfacilitiescangreatlyenhancetheuser’sandprogrammer’sabilitiestoefficientlyusethesystem

AnothersetofOSfunctionsexistsforensuringtheefficientoperationofthesystemitselfviaresourcesharing

Resourceallocation-When multipleusersormultiplejobsrunningconcurrently,resourcesmustbeallocatedtoeachofthem

Manytypesofresources- Some（suchasCPUcycles,mainmemory,andfilestorage）mayhavespecialallocationcode,others（suchasI/Odevices）mayhavegeneralrequestandreleasecode

Accounting-Tokeeptrackofwhichusersusehowmuchandwhatkindsofcomputerresources

Protectionandsecurity-Theownersofinformationstoredinamultiuserornetworkedcomputersystemmaywanttocontroluseofthatinformation,concurrentprocessesshouldnotinterferewitheachother

Protectioninvolvesensuringthatallaccesstosystemresourcesiscontrolled

Securityofthesystemfromoutsidersrequiresuserauthentication,extendstodefendingexternalI/Odevicesfrominvalidaccessattempts

Ifasystemistobeprotectedandsecure,precautionsmustbeinstitutedthroughoutit.Achainisonlyasstrongasitsweakestlink.

CommandLineInterface（CLI）orcommandinterpreterallowsdirectcommandentry

Sometimesimplementedinkernel,sometimesbysystemsprogram

Sometimesmultipleflavorsimplemented–shells

Primarilyfetchesacommandfromuserandexecutesit

●Sometimescommandsbuilt-in,sometimesjustnamesofprograms

●Ifthelatter,addingnewfeaturesdoesn’trequireshellmodification

GUI  User-friendlydesktopmetaphorinterface

Usuallymouse,keyboard,andmonitor

Iconsrepresentfiles,programs,actions,etc

Variousmousebuttonsoverobjectsintheinterfacecausevariousactions（provideinformation,options,executefunction,opendirectory（knownasafolder）

InventedatXeroxPARC

ManysystemsnowincludebothCLIandGUIinterfaces

MicrosoftWindowsisGUIwithCLI“command”shell

AppleMacOSXas“Aqua”GUIinterfacewithUNIXkernelunderneathandshellsavailable

SolarisisCLIwithoptionalGUIinterfaces（JavaDesktop,KDE）

SystemCalls

ProgramminginterfacetotheservicesprovidedbytheOS

Typicallywritteninahigh-levellanguage（CorC++）

Mostlyaccessedbyprogramsviaahigh-levelApplicationProgramInterface（API）ratherthandirectsystemcalluse

ThreemostcommonAPIsare

Win32APIforWindows,

POSIXAPIforPOSIX-basedsystems（includingvirtuallyallversionsofUNIX,Linux,andMacOSX）,and

JavaAPIfortheJavavirtualmachine（JVM）

TypesofSystemCalls

Processcontrol

Filemanagement

Devicemanagement

Informationmaintenance

Communications

Protection

VirtualMachines

Avirtualmachinetakesthelayeredapproachtoitslogicalconclusion. 

Ittreatshardwareandtheoperatingsystemkernelasthoughtheywereallhardware

Avirtualmachineprovidesaninterfaceidenticaltotheunderlyingbarehardware

Theoperatingsystemhostcreatestheillusionthataprocesshasitsownprocessorand（virtualmemory）

Eachguestprovidedwitha（virtual）copyofunderly