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Volatile

RAM

• 7)AM 2e9$9+ 77) S7)AM3

• S)AM

In development

  T-RAM

  Z-RAM

Historical

• Williams:;ilburn tube 23

• 7ela" line memor" 23

• Selectron tube 2

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Early stae NVRAM

• n%S)AM

•

Fe)AM

• M)AM

• P)AM

Mec!anical

• Ma$netic tape

• .ard disk dri%e

• ptical disc dri%e

In development

• @7 XPoint

• CB)AM

• S-S

• ))AM

• )acetrack memor"

•  -)AM

•

Millipede memor"

• F )AM

Historical

• Paper data stora$e 2?3

• 7rum memor" 2

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• Ma$netic(core memor" 2

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Contents

• < .istor"

•

Kolatile memor"

• @ -on(%olatile memor"

• , Mana$ement o! memor" 

o ,9< Memor" mana$ement bu$s

o ,9 4arl" computer s"stems

o ,9@ Kirtual memor"

o ,9, Protected memor"

• ? See also

• Footnotes

• > )e!erences

• E 4#ternal links

History

7etail o! the back o! a section o! 4-IAC+ showin$ %acuum tubes

In the earl"

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o! in!ormation in the !orm o! sound wa%es propa$atin$ throu$h mercur"+ with the Huart5cr"stals actin$ as transducers to read and write bits9 7ela" line memor" would be limited to acapacit" o! up to a !ew hundred thousand bits to remain e!!icient9

Two alternati%es to the dela" line+ the Williams tube and Selectron tube+ ori$inated in

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Non-volatile memory

Solid(state dri%es are one e#ample o! non(%olatile memor"9Main articleL -on(%olatile memor"

 -on(%olatile memor" is computer memor" that can retain the stored in!ormation e%en whennot powered9 4#amples o! non(%olatile memor" include read(onl" memor" 2see )M3+ !lashmemor"+ @7 XPoint+ most t"pes o! ma$netic computer stora$e de%ices 2e9$9 hard disk dri%es+ !lopp" disks and ma$netic tape3+ optical discs+ and earl" computer stora$e methods such as

 paper tape and punched cards9

Forthcomin$ non(%olatile memor" technolo$ies include Fe)AM+ CB)AM+ P)AM+ S-S+))AM+ racetrack memor"+  -)AM and millipede memor"9

Manaement of memory

Main articleL Memor" mana$ement

Proper mana$ement o! memor" is %ital !or a computer s"stem to operate properl"9 Modernoperatin$ s"stems ha%e comple# s"stems to properl" mana$e memor"9 Failure to do so canlead to bu$s+ slow per!ormance+ and at worst case+ takeo%er b" %iruses and maliciousso!tware9

 -earl" e%er"thin$ a computer pro$rammer does reHuires him or her to consider how tomana$e memor"9 4%en storin$ a number in memor" reHuires the pro$rammer to speci!" howthe memor" should store it9

Memory manaement "us

Improper mana$ement o! memor" is a common cause o! bu$s+ includin$ the !ollowin$ t"pesL

• In an arithmetic o%er!low+ a calculation results in a number lar$er than the allocatedmemor" permits9 For e#ample+ a si$ned E(bit inte$er allows the numbers N

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Protected memor" is a s"stem where each pro$ram is $i%en an area o! memor" to use and isnot permitted to $o outside that ran$e9 'se o! protected memor" $reatl" enhances both thereliabilit" and securit" o! a computer s"stem9

Without protected memor"+ it is possible that a bu$ in one pro$ram will alter the memor"

used b" another pro$ram9 This will cause that other pro$ram to run o!! o! corrupted memor"with unpredictable results9 I! the operatin$ s"stems memor" is corrupted+ the entire computer s"stem ma" crash and need to be rebooted9 At times pro$rams intentionall" alter the memor"used b" other pro$rams9 This is done b" %iruses and malware to take o%er computers9

Protected memor" assi$ns pro$rams their own areas o! memor"9 I! the operatin$ s"stemdetects that a pro$ram has tried to alter memor" that does not belon$ to it+ the pro$ram isterminated9 This wa"+ onl" the o!!endin$ pro$ram crashes+ and other pro$rams are nota!!ected b" the error9

Protected memor" s"stems almost alwa"s include %irtual memor" as well9

$ee also

Wikimedia Commons has media related to Computer memory9

• Kirtual memor"

• Semiconductor memor"

• Memor" $eometr"

• Memor" hierarch"

%ootnotes

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•  Memor- and #torage 9echnolog-$ andria$ 6irginia; 9ime 7ife /ooks$ 1++

E&ternal lin's

•

.ow Computer Memor" Works+ b" e!! T"son

Aut!ority

control  • -7L ,

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