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OSdata.com: low memory 

OSdata.com

Low memory

    Summary: Low memory is the memory at the beginning of the address space. Some processors use designated low memory addresses during power on, exception processing, interrupt processing, and other hardware conditions. Some operating systems use designated low memory addresses for global system variables, global system structures, jump tables, and other system purposes.

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PC-DOS and MS-DOS low memory

    Addresses are hexadecimal in segment:offset form.

BIOS Communication Area

0000:0400h-0000:04ABh

    0000:0400h-000:0407h   addresses of RS232 adaptors

    0000:0408h-0000:040Fh   addresses of printers

    0000:0410h-0000:0411h   equipment flag: Also returned by interrupt 11h. MS-DOS only sets this value at startup. Programs that switch video adapters or switch modes in mulitadapter video cards should correctly set bit pair 5:4 — 00=not used, 01=CGA card 40 columns, 10=CGA card 80 columns, 11=monochrome card

    0000:0412h   initialization flag

    0000:0413h-0000:0414h   memory size: normally accessed via interrupt 12h.

    0000:0415h-0000:0416h   amount of memory in I/O channel

    0000:0417h-0000:043Dh   keyboard data area 1: keyboard status flags and 15-byte keyboard buffer. Normally read via interrupt 16h.

    0000:043Eh-0000:0448h   diskette data

    0000:0449h-0000:0466h   video control data area 1: normally accessed via interrupt 10h.

    0000:00467h--0000:046Bh   cassette data; in some models of PS/2 this contains the far (doubleword) address of the code that resets the computer while preserving memory.

    0000:046Ch-0000:0470h   time data: normally accessed via interrupt 1Ah.

    0000:0471h   break flag: set to 1 if the break key has been pressed.

    0000:0472h-0000:0473h   reset flag: if set to 1234h, the BIOS initialization routine (starting at segment FFFFh) will bypass the memory check normally performed during a cold boot. In many models of the PS/2, if the flag is set to 4321h, the system will perform a reset operation without erasing memory.

Reserved

0000:04ACh-0000:04EFh

    Reserved for BIOS.

Inter-Application (User) Communication Area

0000:04F0h-0000:04FFh

    May be used by any program in any way. Originally intended for communications and exchange of data between programs, but because Microsoft couldn’t figure out a standard, the area is in complete anarchy and programs should assume that other programs will act destructively on any attempts to use the area.

DOS Communication Area

0000:0500h-0000:05FFh

    Reserved for use by DOS and BASIC.

    0000:0500   print screen status flag: one byte value — 0=print screen not active or successful termination, 1=print screen in progress, 255=error occurred during print screen.

Macintosh low memory

    0x0000   unassigned

    0x0004   ResetSPPC

    0x0008   BusError

    0x000C   AddrErr

    0x0010   Illegal

    0x0014   ZeroDiv

    0x0018   ChkError

    0x001C   TrapVErr

    0x0020   Privileg

    0x0024   Trace

    0x0028   Line1010

    0x002C   Line 1111

    0x0030   unassigned

    0x0034   Coproces

    0x0038   FmtErrVect

    0x003C   Uninited

    0x0040   Unassig2

    0x0060   Spurious

    0x0064   AutoInt1

    0x0068   AutoInt2

    0x006C   AutoInt3

    0x0070   AutoInt4

    0x0074   AutoInt5

    0x0078   AutoInt6

    0x007C   AutoInt7

    0x0080   TRAPtble

    0x00C0   FP-68881

    0x00DC   reserved

    0x00E0   PMMU

    0x00E0   SMgrOldCore

    0x00EC   reserved

    0x0100   MonkeyLives

    0x0100   SysCom

    0x0102   ScrVRes

    0x0104   ScrHRes

    0x0106   ScreenRow

    0x0108   MemTop

    0x010C   BufPtr

    0x0110   StkLowPtr

    0x0114   HeapEnd

    0x0118   TheZone

    0x011C   UTableBase

    0x0120   MacJmp

    0x0124   DskRtnAdr

    0x0128   PollRtnAdr

    0x012C   DskVerify

    0x012D   LoadTrap

    0x012E   MmInOK

    0x012F   CPUFlag

    0x012F   DskWr11

    0x0130   ApplLimit

    0x0134   SonyVars

    0x0138   PWMValue

    0x013A   PollStack

    0x013E   PollProc

    0x0142   DskErr

    0x0144   SysEvtMask

    0x0146   SysEvtBuf

    0x014A   EventQueue

    0x0154   EvtBufCnt

    0x0156   RndSeed

    0x015A   SysVersion

    0x015C   SEvtEnb

    0x015D   DSWndUpdate

    0x015E   FontFlag

    0x015F   IntFlag

    0x0160   VBLQueue

    0x016A   Ticks

    0x016E   MBTicks

    0x0172   MBState

    0x0173   Tocks

    0x0174   KeyMap

    0x017C   KeyPadMap

    0x0180   unknown

    0x0184   KeyLast

    0x0186   KeyTime

    0x018A   KeyRepTime

    0x018E   KeyThresh

    0x0190   KeyRepThresh

    0x0192   Lvl1DT

    0x01B2   Lvl2DT

    0x01D2   UnitNtryCnt

    0x01D4   VIA

    0x01D8   SCCRd

    0x01DC   SCCWr

    0x01E0   IWM

    0x01E4   GetParam

    0x01F8   SysParam

    0x01F8   SPValid

    0x01F9   SPATalkA

    0x01FA   SPATalkB

    0x01FB   SPConfig

    0x01FC   SPPortA

    0x01FE   SPPortB

    0x0200   SPAlarm

    0x0204   SPFont

    0x0206   SPKbd

    0x0207   SPPrint

    0x0208   SPVolCtl

    0x0209   SPClikCaret

    0x020A   SPMisc1

    0x020B   CDeskPat

    0x020C   Time

    0x0210   BootDrive

    0x0212   JShell

    0x0214   SFSaveDisk

    0x0216   KbdVars

    0x0218   KbdLast

    0x021A   JKybdTask

    0x021E   KbdType

    0x021F   AlarmState

    0x0220   MemErr

    0x0222   JFigTrkSpd

    0x0226   JDiskPrime

    0x022A   JRdAddr

    0x022E   JRdData

    0x0232   JWrData

    0x0236   JSeek

    0x023A   JSetUpPoll

    0x023E   JRecal

    0x0242   JControl

    0x0246   JWakeUp

    0x024A   JReSeek

    0x024E   JMakeSpdTbl

    0x0252   JAdrDisk

    0x0256   JSetSpeed

    0x025A   NiblTbl

    0x025E   FlEvtMask

    0x0260   SdVolume

    0x0261   Finder

    0x0262   SoundVars

    0x0262   SoundPtr

    0x0266   SoundBase

    0x026A   SoundVBL

    0x027A   SoundDCE

    0x027E   SoundActive

    0x027F   SoundLevel

    0x0280   CurPitch

    0x0282   SoundLast

    0x0282   Switcher

    0x0286   SwitcherTPtr

    0x028A   RSDHndl

    0x028E   ROM85

    0x0290   PortAUse

    0x0291   PortBUse

    0x0292   ScreenVars

    0x029A   JGNEFilter

    0x029E   Key1Trans

    0x02A2   Key2Trans

    0x02A6   SysZone

    0x02AA   ApplZone

    0x02AE   ROMBase

    0x02B2   RAMBase

    0x02B6   BasicGlob

    0x02B6   ExpandMem

    0x02BA   DSAlertTab

    0x02BE   ExtStsDT

    0x02CE   SCCASts

    0x02CF   SCCBSts

    0x02D0   SerialVars

    0x02D8   ABusVars

    0x02E0   FinderName

    0x02F0   DoubleTime

    0x02F4   CaretTime

    0x02F8   ScrDmpEnb

    0x02F9   ScrDmpType

    0x02FA   TagData

    0x02FC   BufTgFNum

    0x0300   BufTgFFlg

    0x0302   BufTgFBkNum

    0x0304   BufTgDate

    0x0308   DrvQHdr

    0x0312   PWMBuf2

    0x0316   MacPgm

    0x031A   Lo3Bytes

    0x031E   MinStack

    0x0322   DefltStack

    0x0326   MMDefFlags

    0x0328   GZRootHnd

    0x032C   GZRootPtr

    0x0330   GZMoveHnd

    0x0334   DSDrawProc

    0x0338   EjectNotify

    0x033C   IAZNotify

    0x0340   CkdDB

    0x0342   NxtDB

    0x0344   MaxDB

    0x0346   FlushOnly

    0x0347   RegRscr

    0x0348   FLckUnlck

    0x0349   FrcSync

    0x034A   NewMount

    0x034C   DrMstrBlk

    0x034E   FCBSPtr

    0x0352   DefVCBPtr

    0x0356   VCBQHdr

    0x0360   FSBusy

    0x0362   FSQHead

    0x0366   FSQTail

    0x036A   RgSvArea

    0x0372   WDCBsPtr

    0x0376   HFSVars

    0x0384   DefVRefnum

    0x0392   HFSDSErr

    0x0398   CurDirStore

    0x03A2   ErCode

    0x03A4   Params

    0x03D6   FSTemp8

    0x03DE   FSTemp4

    0x03E2   FSQueueHook

    0x03E6   ExtFSHook

    0x03EA   DskSwtchHook

    0x03EE   RegstVol

    0x03F2   ToExtFS

    0x03F6   FSFCBLen

    0x03F8   DSAlertRect

    0x0400   OSTable

    0x0800   GrafBegin

    0x0800   JHideCursor

    0x0804   JShowCursor

    0x0808   JShieldCursor

    0x080C   JScrnAddr

    0x0810   JScrnSize

    0x0814   JInitCursor

    0x0818   JSetCrsr

    0x081C   JCrsrObscure

    0x0820   JUpdateProc

    0x0824   ScrnBase

    0x0828   MTemp

    0x082C   RawMouse

    0x0830   Mouse

    0x0834   CrsrPin

    0x083C   CrsrRect

    0x0844   TheCrsr

    0x0888   CrsrAddr

    0x088C   JAllocCrsr

    0x0890   JSetCCrsr

    0x0894   JOpcodeProc

    0x0898   CrsrBase

    0x089C   CrsrDevice

    0x08A0   SrcDevice

    0x08A4   MainDevice

    0x08A8   DeviceList

    0x08AC   CrsrRow

    0x08AE   unknown

    0x08B0   QDColors

    0x08CC   CrsrVis

    0x08CD   CrsrBusy

    0x08CE   CrsrNew

    0x08CF   CrsrCouple

    0x08D0   CrsrState

    0x08D2   CrsrObscure

    0x08D3   CrsrScale

    0x08D4   unknown

    0x08D6   MouseMask

    0x08DA   MouseOffset

    0x08DE   JournalFlag

    0x08E0   JSwapFont

    0x08E4   WidthListHand

    0x08E8   JournalRef

    0x08EA   unknown

    0x08EC   CrsrThresh

    0x08EE   JCrsrTask

    0x08F2   WWExist

    0x08F3   QDExist

    0x08F4   JFetch

    0x08F8   JStash

    0x08FC   JIODone

    0x0900   CurApRefNum

    0x0902   LaunchFlag

    0x0903   FondState

    0x0904   CurrentA5

    0x0908   CurStackBase

    0x090C   LoadFiller

    0x0910   CurApName

    0x0930   SaveSegHandle

    0x0934   CurJTOffset

    0x0936   CurPageOption

    0x0938   HiliteMode

    0x0939   unknown

    0x093A   LoaderPBlock

    0x0944   PrintErr

    0x0946   ChooserBits

    0x0954   CoreEditVars

    0x0960   ScrapSize

    0x0964   ScrapHandle

    0x0968   ScrapCount

    0x096A   ScrapState

    0x096C   ScrapName

    0x0970   ScrapTag

    0x0980   RomFont0

    0x0984   ApFontID

    0x0986   SaveFondFlags

    0x0987   FMDefaultSize

    0x0988   CurFMInput

    0x098A   CurFMSize

    0x098C   CurFMFace

    0x098D   CurFMNeedBits

    0x098E   CurFMDevice

    0x0990   CurFMNumer

    0x0994   CurFMDenom

    0x0998   FOutError

    0x099A   FOutFontHandle

    0x099E   FOutBold

    0x099F   FOutItalic

    0x09A0   FOutULOffset

    0x09A1   FOutULShadow

    0x09A2   FOutULThick

    0x09A3   FOutShadow

    0x09A4   FOutExtra

    0x09A5   FOutAccent

    0x09A6   FOutDescent

    0x09A7   FOutWidMax

    0x09A8   FOutLeading

    0x09A9   FOutUnused

    0x09AA   FOutNumer

    0x09AE   FOutDenom

    0x09B2   FMDotsPerInch

    0x09B6   FMStyleTab

    0x09CE   ToolScratch

    0x09D6   WindowList

    0x09DA   SaveUpdate

    0x09DC   PaintWhite

    0x09DE   WMgrPort

    0x09E2   DeskPort

    0x09E6   OldStructure

    0x09EA   OldContent

    0x09EE   GrayRgn

    0x09F2   SaveVisRgn

    0x09F6   DragHook

    0x09FA   TempRect

    0x0A02   OneOne

    0x0A06   MinusOne

    0x0A0A   TopMenuItem

    0x0A0C   AtMenuBotom

    0x0A0E   IconBitMap

    0x0A1C   MenuList

    0x0A20   MBarEnable

    0x0A22   CurDeKind

    0x0A24   MenuFlash

    0x0A26   TheMenu

    0x0A28   SavedHandle

    0x0A2C   MBarHook

    0x0A30   MenuHook

    0x0A34   DragPattern

    0x0A3C   DeskPattern

    0x0A44   DragFlag

    0x0A46   CurDragAction

    0x0A4A   FPState

    0x0A50   TopMapHndl

    0x0A54   SysMapHndl

    0x0A58   SysMap

    0x0A5A   CurMap

    0x0A5C   ResReadOnly

    0x0A5E   ResLoad

    0x0A60   ResErr

    0x0A62   TaskLock

    0x0A63   FScaleDisable

    0x0A64   CurActivate

    0x0A68   CurDeactive

    0x0A6C   DeskHook

    0x0A70   TEDoText

    0x0A74   TERecal

    0x0A78   ApplScratch

    0x0A84   GhostWindow

    0x0A88   CloseOrnHook

    0x0A8C   ResumeProc

    0x0A90   SaveProc

    0x0A94   SaveSP

    0x0A98   ANumber

    0x0A9A   ACount

    0x0A9C   DABeeper

    0x0AA0   DAStrings

    0x0AB0   TEScrpLength

    0x0AB2   unknown

    0x0AB4   TEScrpHandle

    0x0AB8   AppPacks

    0x0AD8   SysResName

    0x0AE8   SoundGlue

    0x0AEC   AppParmHandle

    0x0AF0   DSErrCode

    0x0AF2   ResErrProc

    0x0AF6   TEWdBreak

    0x0AFA   DlgFont

    0x0AFC   LastTGlobal

    0x0B00   TrapAgain

    0x0B04   KeyMVars

    0x0B06   ROMMapHndl

    0x0B0A   PWMBuf1

    0x0B0E   BootMask

    0x0B10   WidthPtr

    0x0B14   AtalkHk1

    0x0B18   AtalkHk2

    0x0B1C   FourDHack

    0x0B20   unknown

    0x0B22   HWCfgFlags

    0x0B24   TimeSCSIDB

    0x0B26   TopMenuItem

    0x0B28   AtMenuBottom

    0x0B2A   WidthTabHandle

    0x0B2E   SCSIDrvrs

    0x0B30   TimeVars

    0x0B34   BtDskRfn

    0x0B36   BootTmp8

    0x0B3E   unknown

    0x0B3F   T1Arbitrate

    0x0B4C   JDiskSel

    0x0B44   JSendCmd

    0x0B48   JDCDReset

    0x0B4C   LastSPExtra

    0x0B50   AppleShare

    0x0B54   MenuDisable

    0x0B58   MBDFHndl

    0x0B5C   MBSaveLoc

    0x0B60   BNMQHd

    0x0B64   Twitcher1

    0x0B68   unknown

    0x0B7C   Twitcher2

    0x0B80   RMgrHiVars

    0x0B9E   RomMapInsert

    0x0B9F   TmpResLoad

    0x0BA0   IntlSpec

    0x0BA0   SMgrCore

    0x0BA4   RMgrPerm

    0x0BA5   WordRedraw

    0x0BA6   SysFontFam

    0x0BA8   SysFontSize

    0x0BAA   MBarHeight

    0x0BAC   TESysJust

    0x0BAE   HiHeapMask

    0x0BB2   SegHiEnable

    0x0BB3   FDevDisable

    0x0BB4   CMVector

    0x0BB8   XFSGlobs

    0x0BBC   ShutDownQHdr

    0x0BC0   NewUnused

    0x0BC2   LastFOND

    0x0BC6   FONDID

    0x0BC8   App2Packs

    0x0BE8   MAErrProc

    0x0BEC   MASuperTab

    0x0BF0   MimeGlobs

    0x0BF4   FractEnable

    0x0BF5   UsedWidths

    0x0BF6   FScaleHFact

    0x0BFA   FScaleVFact

    0x0BFE   unknown

    0x0C00   SCSIBase

    0x0C04   SCSIDMA

    0x0C08   SCSIHsk

    0x0C0C   SCSIGlobals

    0x0C10   RGBBlack

    0x0C16   RGBWhite

    0x0C1C   unknown

    0x0C20   RowBits

    0x0C22   ColLines

    0x0C24   ScreenBytes

    0x0C28   IOPMgrVars

    0x0C2C   NMIFlag

    0x0C2D   VidType

    0x0C2E   VidMode

    0x0C2F   SCSIPoll

    0x0C30   SEVarBase

    0x0CB0   MMUFlags

    0x0CB1   MMUType

    0x0CB2   MMU32bit

    0x0CB3   WhichBox

    0x0CB4   MMUTbl

    0x0CB8   MMUTblSize

    0x0CBC   SInfoPtr

    0x0CC0   ASCBase

    0x0CC4   SMGlobals

    0x0CC8   TheGDevice

    0x0CCC   CQDGlobals

    0x0CD0   AuxWinHead

    0x0CD4   AuxCtlHead

    0x0CD8   DeskCPat

    0x0CDC   SetOSDefKey

    0x0CE0   LastBinPat

    0x0CE8   DeskPatEnable

    0x0CEA   unknown

    0x0CF8   ADBBase

    0x0CFC   WarmStart

    0x0D00   TimeDBRA

    0x0D02   TimeSCCDB

    0x0D04   SlotQDT

    0x0D08   SlotPrTbl

    0x0D0C   SlotVBLQ

    0x0D10   ScrnVBLPtr

    0x0D14   SlotTICKS

    0x0D18   PowerMgrVars

    0x0D1C   AGBHandle

    0x0D20   TableSeed

    0x0D24   SRsrcTblPtr

    0x0D28   JVBLTask

    0x0D2C   WMgrCPort

    0x0D30   VertRRate

    0x0D32   SynListHandle

    0x0D36   LastFore

    0x0D3E   LastMode

    0x0D40   LastDepth

    0x0D42   FMExist

    0x0D43   SavedHilite

    0x0D44   unknown

    0x0D50   MenuCInfo

    0x0D54   MBProcHndl

    0x0D58   MBSaveLoc

    0x0D58   MRect

    0x0D5C   MBFlash

    0x0D5C   MenuCInfo

    0x0D60   ChunkyDepth

    0x0D62   CrsrPtr

    0x0D64   unknown

    0x0D66   PortList

    0x0D6A   MickeyBytes

    0x0D6E   QDErr

    0x0D70   VIA2DT

    0x0D90   SInitFlags

    0x0D92   DTQFlags

    0x0D92   DTQueue

    0x0D94   DtskQHdr

    0x0D98   DTskQTail

    0x0D9C   JDTInstall

    0x0DA0   HiliteRGB

    0x0DA6   TimeSCSIDB

    0x0DA8   DSCtrAdj

    0x0DAC   IconTLAddr

    0x0DB0   VideoInfoOK

    0x0DB4   EndSRTPtr

    0x0DB8   SDMJmpTblPtr

    0x0DBC   JSwapMMU

    0x0DC0   SdmBusErr

    0x0DC4   LastTxGDevice

    0x0DC8   PmgrHandle

    0x0DCC   LayerPalette

    0x0E00   ToolTable

    0x1E00   SystemHeap

further reading: books:

If you want your book reviewed, please send a copy to: Milo, POB 1361, Tustin, CA 92781, USA.

Price listings are for courtesy purposes only and may be changed by the referenced businesses at any time without notice.

further reading: books: general

    Structured Computer Organization, 4th edition; by Andrew S. Tanenbaum; Prentice Hall; October 1998; ISBN 0130959901; Paperback; 669 pages; $95.00; used by CS 308-273A (Principles of Assembly Languages) at McGill University School of Computer Science


    Computers: An Introduction to Hardware and Software Design; by Larry L. Wear, James R. Pinkert (Contributor), William G. Lane (Contributor); McGraw-Hill Higher Education; February 1991; ISBN 0070686742; Hardcover; 544 pages; $98.60; used by CS 308-273A (Principles of Assembly Languages) at McGill University School of Computer Science

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    Copyright © 2001 Milo

    Last Updated: April 10, 2001

    Created: March 28, 2001

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