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COMPUTERARCHITECTUREIT0205

M.Thenmozhi/Kayalvizhi Jayavel/M.B.PanbuAsst.Prof.(Sr.G)/Asst.Prof.(Sr.G)/Asst.Prof.(O.G)

DepartmentofIT

SRMUniversity,Kattankulathur

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Disclaimer

Thecontentsoftheslidesaresolelyforthepurposeofteachingstudents

atSRMUniversity.AllcopyrightsandTrademarksof

organizations/personsapply

even

if

not

specified

explicitly.

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UNITIV:memoryorganization

MemoryHierarchy

Mainmemory

Auxiliarymemory

Associativememory

Cachememory

Virtual

memory

MemoryManagementHardware

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Memoryhierarchy

MainMemory memoryunitthatcommunicatesdirectlywith

theCPU

Auxiliarymemory

devices

that

provide

backup

storage

(e.g)

magneticdisksandtapes

Cache

memory

high

speed

memory

used

to

increase

the

speed

ofprocessingbymakingprogramsanddataavailabletotheCPU

atarapidrate

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MAINmemory

StaticRandomAccessMemory internalflipflopsthatstorethebinaryinformation

DynamicRAM storesthebinaryinformationintheformof

electric

charges

that

are

applied

to

capacitors ReadOnlyMemory storeprogramsthatarepermanently

residentinthecomputerandfortablesofconstantsthatdonot

changeinvalueoncetheproductionofthecomputeris

completed Bootstraploader functionisstartthecomputersoftware

operatingwhenpoweristurnedon

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Mainmemory

Bootstrapprogramloadsaportionofoperatingsystemfrom

disctomainmemoryandcontrolisthentransferredtooperating

system

RAMchip

utilizes

bidirectional

data

bus

with

three

state

bufferstoperformcommunicationwithCPU

Memoryaddressmap pictorialrepresentationofassigned

addressspaceforeachchipinthesystem

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blockdiagramandfunctiontableofram

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Auxiliarymemory

Accesstime averagetimerequiredtoreachastoragelocation

inmemoryandobtainitscontent

Seektime timerequiredtopositiontheread/writeheadtoa

location Transfertime timerequiredtotransferdatatoorfromthe

device

Transferrate no.ofcharactersorwordsthatthedevicecan

transferper

second

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Associativememory

AssociativememorycanalsobecalledasContentaddressable

memory(CAM)

CAMisaccessedsimultaneouslyandinparallelonthebasisof

datacontent

rather

than

by

specific

address

or

location

AssociativememoryismoreexpensivethanaRAMbecauseeach

cellmusthavestoragecapabilityaswellaslogiccircuits

Argument

register

holds

an

external

argument

for

content

matching

Keyregister maskforchoosingaparticularfieldorkeyinthe

argumentword

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Blockdiagramofassociative

memory

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Onecellofassociativememory

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Match logic will be

explained using

Chalk and Talk

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Cachememory

Localityofreference referencestomemoryatanygiven

intervaltendtobeconfinedwithinafewlocalizedareasof

memory

Cachememory logicallyplacedbetweenCPUandmain

memory

Hitratio ratioofthenumberofhits(successinfindingthe

wordsin

Cache)

to

the

total

CPU

references

to

memory

(hits+misses)

Mapping transformationofdatafrommainmemorytocache

memory

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Cachememory

Threetypes

of

mapping

procedures

Associativemapping storesbothaddressand

contentofthememoryword;Inthematching

process,iftheaddressisfound,the

corresponding12bitdataisreadandsenttothe

CPUDirectmapping consistsofindexfieldandtag

field;no.ofbitsintheindexfieldisequaltothe

numberof

address

bits

required

to

access

the

cachememory;eachwordinthecacheconsists

ofdatawordanditsassociatedtag;hit:tagfieldof

CPUaddress

=tag

field

in

the

cache

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Cachememory

Threetypesofmappingprocedures

Set

Associative

mapping

each

word

of

cache

canstoretwoormorewordsofmemoryunder

thesameindexaddress;whenamissoccursin

setassociative

mapping,

tag

replacement

algorithmshouldbeapplied

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ASSOCIATIVEMAPPINGCACHE

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Virtualmemory

Virtualmemory permittheusertoconstructprogramsasthoughlarge

memoryspacewereavailable,equaltothetotalityoftheauxiliarymemory

Anaddress

used

by

aprogrammer

is

Virtual

address

Setofvirtualaddressesarecalledaddressspace

Anaddressinmainmemoryiscalledalocationorphysicaladdress

Setof

physical

addresses

constitute

memory

space

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Virtualmemory

Addressspace>memoryspaceifvirtualmemoryisavailable.

Mappingavirtualaddress

Virtualaddress

register

stores

virtual

address

Memorymappingtable tomapavirtual

addressto

aphysical

address

Mainmemoryaddressregister storesphysical

address

Addressmapping

can

also

be

done

using

pages

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Memorytableformappingavirtualaddress

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Addressmappingusingpages

Blocks physical

memory

is

broken

down

into

groups

of

equal

size

Page groupsofaddressspaceofthesamesize

Pageframeissometimesusedtodenoteablock

Memorypage

table

consists

of

8words

one

for

each

page

Addressinthepagetabledenotesthepagenumber

Contentofthewordgivestheblocknumberwherethatpageisstored

inmainmemory

Presencebit indicateswhetherthepagehasbeentransferredfrom

auxiliarymemoryintomainmemory

3highorderbitsofthevirtualaddressspecifyapagenumberandan

addressfor

the

memory

page

table.

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Memorymanagementhardware

Basic

components

include: Facilityfordynamicstoragerelocationthatmapslogicalmemory

referencesintophysicalmemoryaddresses

Provisionforstoringcommonprogramsstoredinmemorybydifferent

users

Securityagainstunauthorizedaccessbetweenusersandpreventing

usersfromchangingOSfunctions

Segment setoflogicallyrelatedinstructionsordataelementsassociated

withagivenname(addressgeneratedbyasegmentedprogramislogical

address)

Translationlookasidebuffer(TLB) fastassociativememoryusedtohold

themost

recently

referenced

table

entries

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Exampleoflogicalandphysicaladdresses

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Needforcache

StaticanddynamicRAMComparison

Memoryaddressmapping

Contentaddressablememory function

Localityofreference

Mappingproceduresincachememory

Addressspace

and

memory

space

Needformemorymanagementhardware

Componentsofmemorymanagementhardwareunit

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