Pages

PC-DOS and MS-DOS memory map



high memory
segment
offset
size
contents
0000h
0000h
1024
interrupt vector table

0400h
172
BIOS communication area

04ACh
68
reserved by IBM

04F0h
16
user communication area

0500h
256
DOS communication area

0600h
varies
operating system:
IBMBIO.COM (DOS interface to the BIOS)
IBMDOS.COM (DOS interrupt handlers and interrupt 21h service routines
DOS buffers, control areas, and device drivers
COMMAND.COM (resident portion), interrupt 22h, 23h, and 24h handlers, routine to reload transient portion of COMMAND.COM
memory-resident utilities
transient applications
transient portion of COMMAND.COM
9000h
FFFFh

highest address of user memory
A000h
0000h
128K
reserved area of ROM
A000h
0000h

beginning of area used by EGA and PS/2 video systems
B000h
0000h
4000
monochrome video memory

0800h
16K
color graphics adaptor (CGA) video memory
C000h
0000h
192K
ROM expansion and control area

8000h

ROM for hard disk
D000h


ROM expansion and control area
E000h


ROM expansion and control area
F000h
0000h
16K
reserved ROM

4000h
40K
base system ROM, ROM BASIC

E000h
8K
ROM BIOS
low memory