Bare Machine

Bare Machine

1. B.Tech–CS 2
nd
Year Operating System (KCS-401) Dr.PankajKumar
Operating System
KCS –401
Memory
Dr.Pankaj Kumar
Associate Professor –CSE
SRMGPC Lucknow

2. Outline of the Lecture
B.Tech –CS 2
nd
Year Operating System (KCS-401) Dr. PankajKumar
Bare Machine
Resident Monitor
Multiprogramming with fixed Partition
Multiprogramming with Variable Partition
Fragmentation

3. Bare Machine
B.Tech –CS 2
nd
Year Operating System (KCS-401) Dr. PankajKumar
Baremachineislogicalhardwarewhichisusedtoexecutetheprogramintheprocessorwithout
usingtheoperatingsystem.asofnow,wehavestudiedthatwecan’texecuteanyprocesswithout
theOperatingsystem.ButyeswiththehelpoftheBaremachinewecandothat.
Initially,whentheoperatingsystemsarenotdeveloped,theexecutionofaninstructionisdoneby
directlyonhardwarewithoutusinganyinterferinghardware,atthattimetheonlydrawbackwas
thattheBaremachinesacceptingtheinstructioninonlymachinelanguage,duetothisthose
personwhohassufficientknowledgeaboutComputerfieldareabletooperateacomputer.so
afterthedevelopmentoftheoperatingsystemBaremachineisreferredtoasinefficient.

4. Resident Monitor
B.Tech –CS 2
nd
Year Operating System (KCS-401) Dr. PankajKumar
TheResidentMonitorisacodewhichrunsonBareMachine.Itsactslikeanoperatingsystem
whichcontrolseverythinginsideaprocessorandperformsallthefunctions.TheResident
MonitoristhusalsoknownastheJobSequencerbecauseliketheOperatingsystem,italso
sequencesthejobsandsendsittotheprocessorforexecution.Afterthejobsarescheduled,the
ResidentMonitorloadstheProgramsonebyoneintothemainmemoryaccordingtotheir
sequence.
TheadvantageofusingaResidentMonitoroveranOperatingSystemisthatthereisnogapor
lagbetweentheprogramexecutions.So,theprocessingisfasterintheResidentMonitors.

5. Resident Monitor
B.Tech –CS 2
nd
Year Operating System (KCS-401) Dr. PankajKumar
The Resident Monitors are divided into 3 parts:
1.Control Language Interpreter
The job of the Control Language Interpreter is to read and carry out the instructions line by line
to the next level.
2.Loader
The Loader is the main part of the Resident Monitor. As the name suggests, it Loads all the
required system and application programs into the main memory.
3.Device Driver
The Device Driver Takes care of all the Input-Output devices connected with the system. So, all
the communication that takes place between the user and the system is handled by the Device
Driver. It simply acts as an intermediate between the requests and the response, requests that are
made by the user to the system, and they respond that the system produces to fulfill these
requests.

6. Multiprogramming with fixed Partition
B.Tech –CS 2
nd
Year Operating System (KCS-401) Dr. PankajKumar
Ifweacceptthatmultiprogrammingisagoodidea,wenextneedto
decidehowtoorganizetheavailablememoryinordertomake
effectiveuseoftheresource.Onemethodistodividethememory
intofixedsizedpartitions.Thesepartitionscanbeofdifferentsizes
butonceapartitionhastakenonacertainsizethenitremainsat
thatsize.Thereisnoprovisionforchangingitssize.
•Several users simultaneously compete for system resources
•switch between I/O jobs and calculation jobs for instance
•TotakeadvantageofthissharingofCPU,importantformanyjobstobepresentinmain
memory
•AllowingRelocationandTransfersbetween partitions
•Protectionimplementedbytheuseofseveralboundaryregisters:lowandhighboundary
registers,orbaseregisterwithlength
•Fragmentationoccurs if user programs cannot completely fill a partition -wasteful.

7. Multiprogramming with variable Partition
B.Tech –CS 2
nd
Year Operating System (KCS-401) Dr. PankajKumar
Multi-programmingwithvariablepartitioningisacontiguousmemory
managementtechniqueinwhichthemainmemoryisnotdividedinto
partitionsandtheprocessisallocatedachunkoffreememorythatisbig
enoughforittofit.Thespacewhichisleftisconsideredasthefreespace
whichcanbefurtherusedbyotherprocesses.
Advantages
NoInternalFragmentation
NoLimitationonthesizeoftheprocess
Degreeofmultiprogrammingisdynamic
Disadvantages
ExternalFragmentation
ComplexMemoryAllocation

8. Fragmentation
B.Tech –CS 2
nd
Year Operating System (KCS-401) Dr. PankajKumar
Asprocessesareloadedandremovedfrommemory,thefreememoryspaceisbrokenintolittle
pieces.Ithappensaftersometimesthatprocessescannotbeallocatedtomemoryblocks
consideringtheirsmallsizeandmemoryblocksremainsunused.Thisproblemisknownas
Fragmentation.
Fragmentationisoftwotypes−
Externalfragmentation
Totalmemoryspaceisenoughtosatisfyarequestortoresidea
processinit,butitisnotcontiguous,soitcannotbeused.
Internalfragmentation
Memoryblockassignedtoprocessisbigger.Someportionof
memoryisleftunused,asitcannotbeusedbyanotherprocess.

9. Fragmentation
B.Tech –CS 2
nd
Year Operating System (KCS-401) Dr. PankajKumar
Incompactionthespacesthatarefreeandthespaceswhicharenotallocatedtotheprocessare
combinedandsinglelargememoryspaceismade.
Internal fragmentation External fragmentation
Ininternalfragmentationfixed-sizedmemory,blocks
squaremeasureappointedtoprocess.
Inexternalfragmentation,variable-sizedmemory
blockssquaremeasureappointedtomethod.
Internalfragmentationhappenswhenthemethodor
processislargerthanthememory.
Externalfragmentationhappenswhenthemethod
orprocessisremoved.
Thesolutionofinternalfragmentationisbest-fitblock.
Solutionofexternalfragmentationiscompaction,
pagingandsegmentation.
Internalfragmentationoccurswhenmemoryisdivided
intofixedsizedpartitions.
Externalfragmentationoccurswhenmemoryis
dividedintovariablesizepartitionsbasedonthe
sizeofprocesses.
Thedifferencebetweenmemoryallocatedandrequired
spaceormemoryiscalledInternalfragmentation.
Theunusedspacesformedbetweennon-contiguous
memoryfragmentsaretoosmalltoserveanew
process,iscalledExternalfragmentation.

10. Protection
B.Tech –CS 2
nd
Year Operating System (KCS-401) Dr. PankajKumar
Protectionreferstoamechanismwhichcontrolstheaccessofprograms,processes,orusersto
theresourcesdefinedbyacomputersystem.Wecantakeprotectionasahelpertomulti
programmingoperatingsystem,sothatmanyusersmightsafelyshareacommonlogicalname
spacesuchasdirectoryorfiles.
Need of Protection:
•To prevent the access of unauthorized users and
•To ensure that each active programs or processes in the system uses resources only as the stated
policy,
•To improve reliability by detecting latent errors.