DOS Memory Map

Page Start Address End Address
in Hex
Remarks
Decimal Hex
0 0 00000 0003F Hardware Interrupt Vectors
64 00040 0004F BIOS Interrupt Vectors
128 00080 002FF DOS Interrupt Vectors
768 00300 003FF Stack area during POST and bootstrap routine
1024 00400 004EF BIOS Data Area
1264 004F0 004FF Intra-Application Communications Area
1280 00500 005FF DOS reserved communication area
1536 00600   IBMBIO.COM DOS interface to ROM I/O routines
    006FF IbmDos.Com - Dos interrupt handlers and service routines (int 21 functions)
1792 00700   DOS buffers, control areas, and installed device drivers.
Resident portion of COMMAND.COM
Interrupt handlers for int 22h, 23h, 24h,
Code to reload the transient portion Master environment block, default 64 bytes
Environment for next program
External commands or utilities (COM or EXE files)
User stack for COM files (256 bytes)
Transient portion of COMMAND.COM
1 64k 10000 1FFFF This is the User memory. The lower portion is used up by the overspill from Page 0 and any TSRs which have been loaded.
2 128k 20000 2FFFF
3 192k 30000 3FFFF
4 256k 40000 4FFFF
5 320k 50000 5FFFF
6 384k 60000 6FFFF
7 448k 70000 7FFFF
8 512k 80000 8FFFF
9 576k 90000 9FFFF
A 640k A0000 AFFFF EGA and VGA Graphics Screen memory
B 704k B0000 B1000 Monochrome Display Adapter Screen Memory Hercules Cards
736k B8000 BC000 Screen Memory
BFFFF EGA and VGA Text Screen Memory
Note The PCjr and early Tandy 1000 BIOSs revector direct writes to the B8 area to the Video Gate Array and reserved system RAM
C 768k C0000 C3FFF 16k EGA BIOS C000:001E contains the EGA BIOS signature (the letters IBM)
The IBM Token Ring BIOS
784k C4000 C&FFF nbsp;?
800k C8000 C9FF IBM Expanded Memory Adapter
CBFFF 16k hard disk controller BIOS, drive 0 default
816k CC000 CFFFF  ?
Note The contents of page C is very variable and the details given above are a guide only.
D 832k D0000 D7FFF  ?
848k D4000 D7FFF  ?
864k D8000 DBFFF  ?
880k DC000 DFFFF  ?
NoteThe contents of page D is very variable
E 896k E0000 E3FFF PCjr second ROM cartridge address area
912k E4000 EFFFF Usually Unallocated
NoteThe area from E0000h to EFFFFh is hard wired to an empty ROM on AT machines
F 960k F0000 F3FFF PCjr optional Rom cartridge address area cartridge Basic Reserved by IBM on other machines
976k F4000 F5FFF  ?
984k F6000 FBFFF ROM BASIC
1008k FC000 FFFFF Original BIOS (Compatibility BIOS in PS/2)
Note The area from E0000h to FFFFFh on a PS/2 is used by the System ROM

Back.