| 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 | |||