| physical address of memory area in HEX | short description |
| 00000 - 00400 | Interrupt vectors. The emulator loads this file: c:\emu8086\INT_VECT at the physical address 000000. |
| 00400 - 00500 |
System information area. We use a trick to set some parameters by loading a tiny last part (21 bytes) of INT_VECT in that
area (the size of that file is 1,045 or 415h bytes, so when loaded it takes memory from 00000 to 00415h). this memory block is updated by the emulator when configuration changes, see system information area table. |
| 00500 - A0000 | A free memory area. A block of 654,080 bytes. Here you can load your programs. |
| A0000 - B1000 |
Video memory for vga, monochrome, and other adapters. It is used by video mode 13h of INT 10h. |
| B1000 - B8000 |
Reserved. Not used by the emulator. |
| B8000 - C0000 | 32 kb video memory for color graphics adapter (cga). The emulator uses this memory area to keep 8 pages of video memory. The emulator screen can be resized, so less memory is required for each page, although the emulator always uses 1000h (4096 bytes) for each page (see INT 10h / AH=05h in the list of supported interrupts). |
| C0000 - F4000 | Reserved. |
| F4000 - 10FFEF | ROM BIOS and extensions. the emulator loads BIOS_ROM file at the physical address 0F4000h. addresses of interrupt table points to this memory area to make emulation of the interrupt functions. |
interrupt vector table (memory from 00000h to 00400h)
INT number address in address of
in hex interrupt vector BIOS sub-program
00 00x4 = 00 F400:0170 - CPU-generated,
divide error.
04 04x4 = 10 F400:0180 - CPU-generated,
INTO detected
overflow.
10 10x4 = 40 F400:0190 - video functions.
11 11x4 = 44 F400:01D0 - get BIOS
equipment list.
12 12x4 = 48 F400:01A0 - get memory size.
13 13x4 = 4C F400:01B0 - disk functions.
15 15x4 = 54 F400:01E0 - BIOS functions.
16 16x4 = 58 F400:01C0 - keyboard functions.
17 17x4 = 5C F400:0400 - printer.
19 19x4 = 64 FFFF:0000 - reboot.
1A 1Ax4 = 68 F400:0160 - time functions.
1E 1Ex4 = 78 F400:AFC7 - vector of diskette
controller parameters.
20 20x4 = 80 F400:0150 - DOS function:
terminate program.
21 21x4 = 84 F400:0200 - DOS functions.
33 33x4 = CC F400:0300 - mouse functions.
all the others ??x4 = ?? F400:0100 - default interrupt stub.
A call to BIOS sub-system is
disassembled as BIOS DI (Basic Input/Output System - Do Interrupt). To encode this 4 byte instruction, FFFF opcode prefix is used. for example: FFFFCD10 is used to make the
emulator to execute interrupt number 10h.At address F400:0100 there is this machine code FFFFCDFF (it is decoded as INT 0FFh, it is used to generate a default error message, unless you make your own interrupt replacement for missing functions). |
| address (hex) | size | description |
| 0040h:0010 | WORD |
BIOS equipment list.
bit fields for BIOS-detected installed hardware:
bit(s) Description
15-14 number of parallel devices.
13 reserved.
12 game port installed.
11-9 number of serial devices.
8 reserved.
7-6 number of floppy disk drives (minus 1):
00 single floppy disk;
01 two floppy disks;
10 three floppy disks;
11 four floppy disks.
5-4 initial video mode:
00 EGA,VGA,PGA, or other with on-board video BIOS;
01 40x25 CGA color.
10 80x25 CGA color (emulator default).
11 80x25 mono text.
3 reserved.
2 PS/2 mouse is installed.
1 math coprocessor installed.
0 set when booted from floppy.
|
| 0040h:0013 | WORD |
kilobytes of contiguous memory starting
at absolute address 00000h. this word is also returned in AX by INT 12h. this value is set to: 0280h (640KB). |
| 0040h:004A | WORD |
number of columns on screen. default value: 0032h (50 columns). |
| 0040h:004E | WORD |
current video page start address in video memory default value: 0000h. |
| 0040h:0050 |
contains row and column position for the cursors on each of eight
video pages. default value: 0000h (for all 8 WORDs). |
|
| 0040h:0062 | BYTE |
current video page number. default value: 00h (first page). |
| 0040h:0084 | BYTE |
rows on screen minus one. default value: 13h (19+1=20 columns). |