RAM And ROM

About RAM & ROM. Different types of RAMs & Differences between those RAMs. Also the Different types of ROMs & there differences.

1. By
GihanC. Ranasinghe

2. Memoryisrequiredincomputerstostoredataand
instructions.
Memoryisphysicallyorganizedasalargenumberofcells
thatarecapableofstoringonebiteach.
Logicallytheyareorganizedasgroupsofbitsthatare
assignedanaddress.
Dataandinstructionsareaccessedthrough
thesememoryaddress.
Thespeedwithwhichthesememoryaddressescanbe
accesseddeterminesthecostofthememory.
Fasterthememoryspeed,highertheprice.

3. Computermemorycanbesaidtobeorganizedina
hierarchicalwaywherememorywiththefastestaccess
speedsandhighestcostsliesatthetopwhereasthose
withlowestspeedsandhencelowestcostslieatthe
bottom.
Basedonthiscriteriamemoryisofmaintwotypes.
Maintwotypesare;
PrimaryMemory
SecondaryMemory
AlthoughCacheconsiderasaMemory,itisan
intermediatememory.Soitdoesn'tgroupasaMaintype
ofMemory.

4. Primary Memory
Primarymemoryiscomputermemorythataprocessoror
computeraccessesfirstordirectly.
Itallowsaprocessortoaccessrunningexecution
applicationsandservicesthataretemporarilystoredina
specificmemorylocation.
Primarymemoryisalsoknownasprimarystorageor
mainmemory.
Primarymemoryisconsideredfasterthansecondary
memory.

5. Assoonasacomputerstarts,primarymemoryloadsall
runningapplications,includingthebaseoperatingsystem
(OS),userinterfaceandanyuser-installedandrunning
softwareutility.
Aprogram/applicationthatisopenedinprimarymemory
interactswiththesystemprocessortoperformall
applicationspecifictasks.
TherearetwotypesofPrimaryMemory,
RAM
ROM

6. RAM
Alternativelyreferredtoasmainmemory,primary
memory,orsystemmemory,RandomAccess
Memory(RAM)isahardwaredevicethatallows
informationtobestoredandretrievedonacomputer.
RAMisusuallyassociatedwithDRAM,whichisatype
ofmemorymodule.
Becauseinformationisaccessedrandomlyinsteadof
sequentiallylikeitisonaCDorharddrive,thecomputer
canaccessthedatamuchfaster.

7. Characteristics of RAM
These are semiconductor memories.
It is known as the main memory.
Volatile memory.
Data is lost in case power is switched off.
It is the working memory of the computer.
Faster than secondary memories.
A computer cannot run without the
primary memory.

8. Asthecomputerboots,partsoftheoperatingsystemand
driversareloadedintomemory,whichallowstheCPUto
processtheinstructionsfasterandspeedsuptheboot
process.
Aftertheoperatingsystemhasloaded,eachprogramyou
open,suchasthebrowseryou'reusingtoviewthispage,
isloadedintomemorywhileitisrunning.
Iftoomanyprogramsareopenthecomputer
willswapthedatainthememorybetweentheRAMand
theharddiskdrive.
RAMasweknowittoday,assolidstatememory,wasfirst
inventedin1968byRobertDennard.
Knownspecificallyasdynamicrandomaccessmemory,
orDRAM,transistorswereusedtostorebitsofdata.

9. TherearetwomaincategoriesofRAM;
DRAM
SRAM
Dynamicrandom-accessmemory(DRAM)
DRAMisatypeofrandom-accessmemorythatstores
eachbitofdatainaseparatecapacitorwithinan
integratedcircuit.
Thecapacitorcanbeeitherchargedordischarged.These
twostatesaretakentorepresentthetwovaluesofabit,
conventionallycalled0and1.

10. Staticrandom-accessmemory(staticRAMorSRAM)
SRAMisatypeofsemiconductormemorythat
usesbistablelatchingcircuitry(flip-flop)tostoreeachbit.
SRAMexhibitsdataremanence,butitisstillvolatilein
theconventionalsensethatdataiseventuallylostwhen
thememoryisnotpowered.
ThetermstaticdifferentiatesSRAMfromDRAMwhich
mustbeperiodicallyrefreshed.
SRAMisfasterandmoreexpensivethanDRAM;itis
typicallyusedforCPUcachewhileDRAMisusedfora
computer'smainmemory.

11. SDRAM
SDRAM,whichisshortforSingleDataRAMorSynchronous
DRAM,isatypeofmemorythatsynchronizesitselfwiththe
computer'ssystemclock.
Beingsynchronizedallowsthememorytorunathigher
speedsthanpreviousmemorytypesandalsosupportsupto
133MHzsystembuscycling.
Since1993,thishasbeentheprevalenttypeofmemoryused
incomputersaroundtheworld.
InthepicturebelowisanexampleofaSDRAM.

12. Itwasoneofthefirstmemoryarchitecturestosupport
SynchronousMemoryarchitecturesandwasonlyknown
asSDRAMatitstime.
SingleDataRatemeansthatitcantransferonemachine
word(16bitsforthex86architecture)ofdataduringone
clockcycle.
CommonSDRmemorystandardsincludedPC-100and
PC-133whichranonclockspeedsof100MHzand
133MHzrespectively.

13. DDR
ShortforDoubleDataRate,DDRismemorythatwasfirst
introducedin1996andhassincebeenreplacedbyDDR2.
DDRutilizesboththerisingandfallingedgeofthesystem
clock,potentiallydoublingthespeedofthememory.
Today,DDRtechnologyisfoundonhigh-endvideo
cardsandcomputermemory
DDRimprovedupontheSDRdesignbyprovidingdouble
thedataduringoneclockcycle.
Thisprovidedasignificantincreaseinperformanceover
thetraditionalarchitecture.

14. Formarketingpurposes,DDRmemoryclockshavealways
beenpromotedatspeedstwicetheiroriginalvalue.
Forexample,commonmemorystandardsforDDR
includedDDR-200,DDR-266,DDR-333andDDR-400
whichactuallyhadrespectiveclockspeedsof100MHz,
133MHz,166MHzand200MHz.

15. RDRAM
ShortforRambusDynamicRandomAccess
Memory,RDRAMwasdevelopedbyRambusandfirst
becameavailabletocomputersin1999.
RDRAMisamemorytechnologythatoffersa1.6GB/sof
theoreticalmemorybandwidthandoffersimproved
memoryaccessataslightlyhighercostwhencompared
toSDRAM.
AfterIntel'scontractwithRambusexpiredin2001,Intel
shifteditsfocusprimarilytoDDRSDRAMandtoday,
RDRAMisnotoftenfoundincomputers.

16. DDR2
Shortfordoubledataratetwo,DDR2isthesecond
generationofDDRmemorythatwasreleasedin
Septemberof2003.
DDR2iscapableofoperatingatgreaterspeedsthanDDR,
offersagreaterbandwidthpotential,operatesonless
power,andgenerateslessheat.
Duetoarchitecturaldifferences,DDR2memorymodules
areincompatiblewithDDRslots.

17. DDR3
Shortfordoubledataratethree,DDR3isatypeof
dynamicrandom-accessmemory(DRAM)releasedin
Juneof2007asthesuccessortoDDR2.
DDR3chipshavebusclockspeedof400MHzupto1066
MHz,rangeinsizefrom1to24GB,andconsumenearly
30%lesspowerthantheirpredecessors.
DDR3RAMsticksforadesktopcomputerhave240pins.
Foralaptopcomputer,DDR3RAMstickshave204pins.

18. DDR4
Shortfordoubledataratefour,DDR4isatypeofsystem
memoryknownasSDRAMandwasreleasedin
Septemberof2014asthesuccessortoDDR3.
DDR4hasbusclockspeedsthatrangefrom800to1600
MHzandrangeinstoragecapacityfrom4to128GB
perDIMM(DualIn-lineMemoryModule).
DDR4isalsomoreefficientat1.2Vwhencomparedto
DDR3's1.5to1.65Vrange.

19. Difference between DDR1, DDR2 & DDR3

20. Difference between SDRAM versions….

21. Difference between DDR3 & DDR4

22. ROM
ROMstandsforReadOnlyMemory.
Thisisanon-volatiletypeofmemorywhichisfoundin
computersandotherelectronicsdevices.
Itisusedforstoringdatapermanently.
Thistypeofmemorycannotbemodifiedbythecomputer
butitcanbereadandthereforeitisknownastheread
onlymemory.
Itkeepsthebootstrapprogramwhichrunsonitown
whenthesystemisturnedonorreseteverytime.
SomeofthecommontypesofROMincludePROM,
EPROMandEEPROM.

23. PROM
ItstandsforProgrammableReadOnlyMemory.Itwas
firstdevelopedin70sbyTexasInstruments.
Itismadeasablankmemory.
APROMprogrammerorPROMburnerisrequiredin
ordertowritedataontoaPROMchip.
Thedatastoredinitcannotbemodifiedandthereforeit
isalsoknownasonetimeprogrammabledevice.

24. EPROM
ItstandsforErasableProgrammableROM.
ItisdifferentfromPROMasunlikePROMtheprogram
canbewrittenonitmorethanonce.
Thiscomesasthesolutiontotheproblemfacedby
PROM.Thebitsofmemorycomebackto1,whenultra
violetraysofsomespecificwavelengthfallsintoitschip’s
glasspanel.
Thefusesarereconstitutedandthusnewthingscanbe
writtenonthememory.

25. ItstandsforElectricallyErasableReadOnlyMemory.
ThesearealsoerasablelikeEPROM,butthesameworkof
erasingisperformedwithelectriccurrent.
Thus,itprovidestheeaseoferasingitevenifthememory
ispositionedinthecomputer.Itstorescomputersystem’s
BIOS.
UnlikeEPROM,theentirechipdoesnothavetobeerased
forchangingsomeportionofit.
Thus,itevengetsridofsomebiggestchallengesfacedby
usingEPROMs.
EEPROM