Operating systems unit 1 wicked stockknj

Gghhn

1. Principles of Operating System
Unit -1
Smt M V S V Kiranmai
APCSE (C), UCEK, JNTUK

2. What is an Operating System?
•Aprogramthatactsasanintermediarybetweena
userofacomputerandthecomputerhardware
•Itprovideanenvironmentinwhichausercan
executeprogramsinaconvenientandefficient
manner
•Itisasoftwarethatmanagesthecomputerhardware
•Itisanintermediarybetweenthecomputeruserand
thecomputerhardware.
•Operatingsystemgoals:
–Executeuserprogramsandmakesolvinguser
problemseasier
–Makethecomputersystemconvenienttouse
–Usethecomputerhardwareinanefficientmanner

3. Computer System Structure
•Computer system can be divided into four components:
–Hardware –provides basic computing resources
•CPU, memory, I/O devices
–Operating system
•Controls and coordinates use of hardware among
various applications and users
–Application programs –define the ways in which the
system resources are used to solve the computing
problems of the users
•Word processors, compilers, web browsers,
database systems, video games
–Users
•People, machines, other computers

4. Four Components of a Computer System

6. What Operating Systems Do
•Userswantconvenience,easeofuseandgood
performance-Don’tcareaboutresourceutilization
•shared computer such asmainframe or
minicomputermustkeepallusershappy
•Usersofdedicatesystemssuchasworkstationshave
dedicatedresourcesbutfrequentlyuseshared
resourcesfromservers
•Handheldcomputersareresourcepoor,optimizedfor
usabilityandbatterylife
•Somecomputershavelittleornouserinterface,such
asembeddedcomputersindevicesandautomobiles-
Runprimarilywithoutuserintervention

7. Operating System Definition
•OS is a resource allocator
–Manages all resources
–Decides between conflicting requests for efficient
and fair resource use
•OS is a control program
–Controls execution of programs to prevent errors
and improper use of the computer
–It is especially concerned with the operation and
control of I/O devices.

8. Operating System Definition (Cont.)
•OS-“Theoneprogramrunningatalltimesonthe
computer”isthekernel.
•Everythingelseiseither
–asystemprogram(shipswiththeoperatingsystem),
or
–anapplicationprogram.
•Today’sOSesforgeneralpurposeandmobile
computingalsoincludemiddleware–asetofsoftware
frameworksthatprovideadditionalservicesto
applicationdeveloperssuchasdatabases,multimedia,
graphics

9. Operating-System Operations
•Anoperatingsystemprovidestheenvironmentwithin
whichprogramsareexecuted
•Bootstrapprogram–simplecodetoinitializethesystem,
loadthekernel
•Kernelloads
•Startssystemdaemons(servicesprovidedoutsideofthe
kernel)
•KernelInterruptdriven(hardwareandsoftware)
–Hardwareinterruptbyoneofthedevices
–Softwareinterrupt(exceptionortrap):
•Softwareerror(e.g.,divisionbyzero)
•Requestforoperatingsystemservice-systemcall
•Otherprocessproblemsincludeinfiniteloop,
processesmodifyingeachotherortheoperating
system

10. Multiprogramming (Batch system)
•SingleusercannotalwayskeepCPUand
I/Odevicesbusy
•Multiprogramming organizesjobs(code
anddata)soCPUalwayshasoneto
execute
•Asubsetoftotaljobsinsystemiskeptin
memory
•Onejobselectedandrunviajob
scheduling
•Whenjobhastowait(forI/Oforexample),
OSswitchestoanotherjob
•Multiprogramming increases CPU
utilization,aswellaskeepingusers
satisfied,byorganizingprogramssothat
theCPUalwayshasonetoexecute
•aprograminexecutionistermeda
process
Memory Layout
for
Multiprogrammed
System

11. Multitasking (Timesharing)
•AlogicalextensionofBatchsystems–theCPUswitches
jobssofrequentlythatuserscaninteractwitheachjob
whileitisrunning,creatinginteractivecomputing
–Responsetimeshouldbe<1second
–Eachuserhasatleastoneprogramexecutingin
memoryprocess
–IfseveraljobsreadytorunatthesametimeCPU
scheduling
–Ifprocessesdon’tfitinmemory,swappingmoves
theminandouttorun
–Virtualmemoryallowsexecutionofprocessesnot
completelyinmemory.Themainadvantageofthis
schemeisthatitenablesuserstorunprogramsthat
arelargerthanactualphysicalmemory.

12. •Dual-modeoperationallowsOStoprotectitselfand
othersystemcomponents
–Usermodeandkernelmode
–Modebitprovidedbyhardware
•Providesabilitytodistinguishwhensystemis
runningusercodeorkernelcode
•Whenauserisrunningmodebitis“user”
•Whenkernelcodeisexecutingmodebitis
“kernel”
•Someinstructionsdesignatedasprivileged,only
executableinkernelmode
•Systemcallchangesmodetokernel,returnfrom
callresetsittouser
•IncreasinglyCPUssupportmulti-modeoperations
–i.e.virtualmachinemanager(VMM)modeforguest
VMs
Dual-mode Operation

13. Transition from User to Kernel Mode
kernel mode -also called supervisor mode, system mode, or
privileged mode.

14. •Systemcallsprovidethemeansforauserprogramtoask
theoperatingsystemtoperformtasksreservedforthe
operatingsystemontheuserprogram’sbehalf
•itisthemethodusedbyaprocesstorequestactionbythe
operatingsystem

15. Timer
•Timer to prevent infinite loop / process hogging resources
–Timer is set to interrupt the computer after some time
period
–Keep a counter that is decremented by the physical
clock.
–Operating system set the counter (privileged instruction)
–When counter zero, generate an interrupt
–Set up before scheduling process to regain control or
terminate program that exceeds allotted time

16. Computing Environments -Traditional
•Stand-alonegeneralpurposemachines
•Butblurredasmostsystemsinterconnectwithothers
(i.e.,theInternet)
•Portalsprovidewebaccesstointernalsystems
•Networkcomputers (thinclients)arelikeWeb
terminals-areusedinplaceoftraditionalworkstations
wheremoresecurityoreasiermaintenanceisdesired
•Mobilecomputersinterconnectviawirelessnetworks
•Networkingbecomingubiquitous–evenhomesystems
usefirewallstoprotecthomecomputersfromInternet
attacks

17. Computing Environments -Mobile
•computingonHandheldsmartphones,tablets,etc
•Devicesareportableandlightweight
•mobilesystemsareusednotonlyfore-mailandweb
browsingbutalsoforplayingmusicandvideo,reading
digitalbooks,takingphotos,andrecordingandediting
high-definitionvideo
•Extrafeature–moreOSfeatures(GPS,gyroscope)
•AnembeddedGPSchipallowsamobiledevicetouse
satellitestodetermineitspreciselocationonEarth
•Allowsnewtypesofappslikeaugmentedreality
•UseIEEE802.11wireless,orcellulardatanetworksfor
connectivity
•Thememorycapacityandprocessingspeedofmobile
devices,however,aremorelimitedthanthoseofPCs
•LeadersareAppleiOSandGoogleAndroid

18. Computing Environments –Distributed
•Distributedcomputing
–Collectionofseparate,possiblyheterogeneous,
systemsnetworkedtogether
•Networkisacommunicationspath,TCP/IPmost
common
–LocalAreaNetwork(LAN)
–WideAreaNetwork(WAN)
–MetropolitanAreaNetwork(MAN)
–PersonalAreaNetwork(PAN)
–NetworkOperatingSystemprovidesfeaturesbetween
systemsacrossnetwork
•Communicationschemeallowssystemstoexchange
messages
•Illusionofasinglesystem

19. Computing Environments –Client-Server
Client-Server Computing
Dumb terminals supplanted by smart PCs
Many systems now servers, responding to requests
generated by clients
General structure of a client–server system

20. Serversystemscanbebroadlycategorizedas
computeserversandfileservers
Compute-serversystemprovidesaninterfaceto
clienttorequestservices(i.e.,database).In
response,theserverexecutestheactionand
sendstheresultstotheclient.
File-serversystemprovidesinterfaceforclients
tostoreandretrievefiles.Itisafile-system
interfacewhereclientscancreate,update,read,
anddeletefiles

21. Computing Environments -Peer-to-Peer (P2P)
•Anothermodelofdistributedsystem
•P2Pdoesnotdistinguishclientsand
servers
–allnodesareconsideredpeers
–eachmayactasclient,serveror
both
–NodemustjoinP2Pnetwork
•Registersitsservicewith
centrallookupserviceon
network,or
•Broadcastrequestforservice
andrespondtorequestsfor
serviceviadiscoveryprotocol
ExamplesincludeNapsterandGnutella,VoiceoverIP
(VoIP)suchasSkype

22. Computing Environments –Cloud Computing
•Deliverscomputing,storage,evenappsasaserviceacross
anetwork
•Logicalextensionofvirtualizationbecauseituses
virtualizationasthebaseforitfunctionality.
–AmazonEC2(AmazonElasticComputeCloud)has
thousandsofservers,millionsofvirtualmachines,
petabytesofstorageavailableacrosstheInternet,pay
basedonusage
•Manytypes
–Publiccloud–availableviaInternettoanyonewilling
topay
–Privatecloud–runbyacompanyforthecompany’s
ownuse
–Hybridcloud–includesbothpublicandprivatecloud
components

23. –SoftwareasaService(SaaS)–oneormoreapplications
availableviatheInternet(i.e.,wordprocessor)
–PlatformasaService(PaaS)–softwarestackreadyfor
applicationuseviatheInternet(i.e.,adatabaseserver)
–InfrastructureasaService(IaaS)–serversorstorage
availableoverInternet(i.e.,storageavailableforbackup
use)
–Cloudcomputingenvironmentscomposedoftraditional
OSes,plusVMMs,pluscloudmanagementtools
–Internetconnectivityrequiressecuritylikefirewalls
–Loadbalancersspreadtrafficacrossmultiple
applications

24. Cloud Computing

25. Computing Environments –Real-Time Embedded
Systems
•Real-timeembeddedsystemsmostprevalentformof
computers
–Varyconsiderable,specialpurpose,limitedpurpose
OS,real-timeOS
–Useexpanding
–haveveryspecifictasks
–theyhavelittleornouserinterface,preferringto
spendtheirtimemonitoringandmanaginghardware
devices,suchasautomobileenginesandroboticarms
•Manyotherspecialcomputingenvironmentsaswell
–SomehaveOSes,someperformtaskswithoutanOS
•Real-timeOShaswell-definedfixedtimeconstraints
–Processingmustbedonewithinconstraint
–Correctoperationonlyifconstraintsmet

26. •EmbeddedsystemsalwaysrunReal-TimeOperating
Systems(RTOS).
•Arealtimesystemisusedwhenrigidtimerequirements
havebeenplacedontheoperationofaprocessororthe
flowofdata;
•itisoftenusedasacontroldeviceinadedicated
application.
•Sensorsbringdatatothecomputer.Thecomputermust
analyzethedataandpossiblyadjustcontrolstomodify
thesensorinputs.
•Areal-timesystemhaswell-defined,fixedtime
constraints.Processingmustbedonewithinthedefined
constraints,orthesystemwillfail
•Ex:Systemsthatcontrolscientificexperiments,medical
imagingsystems,industrialcontrolsystems,certain
displaysystems,automobile-enginefuel-injection
systems,home-appliancecontrollers,andweapon
systems

27. Free and Open-Source Operating Systems
•Operatingsystemsmadeavailableinsource-codeformat
ratherthanjustbinaryclosed-source
•Freesoftware(referredtoasfree/libresoftware)notonly
makessourcecodeavailablebutalsoislicensedtoallow
no-costuse,redistribution,andmodification
•Open-sourcesoftwaredoesnotnecessarilyoffersuch
licensing.
•allfreesoftwareisopensource,someopen-source
softwareisnot“free.”
•GNU/Linuxisthemostfamousopen-sourceoperating
system,withsomedistributionsfreeandothersopen
sourceonly
•Windowsisproprietarysoftware—Microsoftownsit,
restrictsitsuse,andcarefullyprotectsitssourcecode

28. •CountertothecopyprotectionandDigitalRights
Management(DRM)movement
•StartedbyFreeSoftwareFoundation(FSF),whichhas
“copyleft”GNUPublicLicense(GPL)
•ExamplesincludeGNU/LinuxandBSDUNIX(including
coreofMacOSX),andmanymore
•CanuseVMMlikeVMwarePlayer(FreeonWindows),
Virtualbox(opensourceandfreeonmanyplatforms-
http://www.virtualbox.com)
–Usetorunguestoperatingsystemsforexploration