AT & XT Memory Address
----------------------

10000h 1024k  -------------------------------------------------- 
 FC00h 1008k
 F800h  992k  ROM BIOS
 F400h  976k
 F000h  960k  -------------------------------------------------- 
 EC00h  944k
 EC00h  944k
 E800h  928k  Extra ROM for AT                  Free in XT
 E400h  912k
 E000h  896k  --------------------- 
 DC00h  880k  --------------------------------------------------
 D800h  864k  Free in AT
 D400h  848k  ---------------------             XT LIM Data Area
 D000h  832k
 CC00h  816k  LIM Data Area  -----------------------------------
                                                XT Hard disk ROM
 C800h  800k  --------------------------------------------------
 C400h  784k  -------------------------------------------------- 
              EGA & VGA ROM BIOS
 C000h  768k  --------------------------------------------------

 BC00h  752k  --------------------------------------------------
              CGA Video
 B800h  736k  -------------------------------------------------- 

 B400h  720k  --------------------------------------------------
              MDA Video
 B000h  704k  -------------------------------------------------- 
 AC00h  688k
 A800h  672k  EGA & VGA Video RAM GRAPHICS
 A400h  656k
 A000h  640k  -------------------------------------------------- 

===============================================================================

0000 0000 - 0009 FFFF    640k   BASE MEMORY AREA
000A 0000 - 000A FFFF     64k   VIDEO RAM of EGA VGA 8514A
                                in GRAPHICS MODE
000B 0000 - 000B 7FFF     32k   VIDEO RAM of 
                                1.CGA
                                2.HERCULES in GRAPHICS
                                3.EGA VGA 8514A in TEXT MODE
000B 8000 - 000B FFFF     32k   VIDEO RAM of
                                1.MDA
                                2.HERCULES TEXT & GRAPHICS
000C 0000 - 000C 3FFF     16k   ROM BIOS of EGA VGA 8514A
000C 4000 - 000C 7FFF     16k   ROM BIOS of VGA 8514A
000C 8000 - 000C BFFF     16k   ROM BIOS of XT HARD DISK CONTROLLER
000C C000 - 000D FFFF     80k   Open for EXPANSION CARD
000E 0000 - 000E FFFF     64k   IBM ROM BASIC
000F 0000 - 000F 7FFF     32k   SYSTEM ROM BIOS for AT
000F 8000 - 000F DFFF     24k   SYSTEM ROM BIOS
000F E000 - 000F FFFF      8k   SYSTEM ROM BIOS
0010 0000 - 00FF 0000  15296k   Extended memory area

===============================================================================



DMA (8237) Channel Usage
------------------------
DMA 0  Available on AT,  DRAM refresh on XT 
DMA 1  Available on I/O slot
DMA 2  Floppy Diskette controller
DMA 3  Available on I/O slot
--------------------------------------+
DMA 4  Cascade for channel 0 - 3      |
DMA 5  Available on I/O slot          | NOT AVAILABLE FOR XT's
DMA 6  Available on I/O slot          |
DMA 7  Available on I/O slot          |
--------------------------------------+

===============================================================================

Timer/Counter Channels (8253/8254)
----------------------------------
TC 0  System timer tick,generate IRQ 0
TC 1  DRAM refresh request, triggers refresh cycle for AT
TC 1  DRAM refresh request, triggers DMA DRQ 0 for XT
TC 2  Speaker tone generator (Programmable)

===============================================================================

Hardware Interrupt Channels (8259)
----------------------------------
IRQ 0  Timer channel
IRQ 1  Keyboard
IRQ 2  Cascade IRQ8-IRQ15 (Becomes IRQ 9)
       (Available on XT's)
IRQ 3  Second & Fourth RS-232C port
IRQ 4  First  & Third  RS-232C port
IRQ 5  Second parallel port 
       (Hard disk controller for XT's)
IRQ 6  Floppy disk controller
IRQ 7  First parallel port
-------------------------------------------+
IRQ 8  Real time clock                     |
IRQ 9  BIOS redirected to INT 0A(H)        |
IRQ 10 Available                           |
IRQ 11 Available                           |
IRQ 12 Available                           | NOT AVAILABLE FOR XT's
IRQ 13 Coprocessor (80287,80387) exeption  |
IRQ 14 Hard disk controller for AT         |
IRQ 15 Available                           |
-------------------------------------------+

===============================================================================



I/O Space
---------
000-00F   First DMA Controller (8237)
010-01F   Available for expansion adapter
020-021   First interrupt controller (8259A)
022-03F   Reserved by IBM, seldom used
040-047   Timer/counter 
          (8253 for XT / 8254 for AT)
048-04F   Reserved by IBM, seldom used
050-05F   Reserved by IBM, seldom used
060-064   8255 ports for XT
          8042 controller for AT
065-06F   Reserved by IBM, seldom used
070-071   Real time clock for AT
072-07F   Reserved by IBM, seldom used
080-08F   DMA page registers
090-09F   Reserved by IBM, seldom used
0A0-0A1   NMI mask register for XT
          Second interrupt controller for AT
0A2-0Af   Reserved by IBM, seldom used
0B0-0BF   Reserved by IBM, seldom used
0C0-0CF   Second DMA controller for AT
0D0-0DF   Reserved by IBM, seldom used
0E0-0EF   Available
0F0-0FF   Math coprocessor for AT (80287 or 80387)
100-1EF   Available
1F0-1FF   Hard disk controller for AT
200-207   Games ports adapter
208-20F   Available
210-21F   Expansion unit for XT
220-26F   Available
270-277   Reserved by IBM, seldom used
278-27F   Second parallel printer port
280-2AF   Available
2B0-2DF   EGA adapter alternate I/O address
          IBM 3270 emulator use's 2D0-2DF
2E8-2EF   Fourth Serial Port
2E0-2EF   Available
2F0-2F7   Reserved by IBM, seldom used
2F8-2FF   Second RS-232C adapter
300-31F   Available
320-32F   Hard disk controller for XT
330-36F   Available
370-377   Reserved by IBM, seldom used
378-37F   First parallel printer port
380-38F   SDLC adapter
390-3AF   Available
3B0-3BB   Reserved by IBM, seldom used
3BC-3BF   Monochrome display adapter
3C0-3CF   EGA/VGA
3D0-3DF   CGA
3E0-3EF   Available
3F0-3F7   Floppy disk controller
3F8-3FF   First RS-232C adapter


Description                     PC/XT       AT          PCjr
-------------------------------------------------------------------------------
DMA Controller 1                000h-00Fh   000h-01Fh   ...
Interrupt Controller 1          020h-021h   020h-03Fh   020h-027h
Timer                           040h-043h   040h-05Fh   040h-047h
PPI (Keyboard)                  060h-063h   ...         060h-067h
AT Keyboard                     ...         060h-06Fh   ...
DMA Page Register               080h-083h   080h-09Fh   ...
NMI Mask Register               0Ah         070h-07Fh   0A0h-0A7h
AT Interrupt Controller 2       ...         0A0h-0BFh   ...
PCjr Sound Generator            ...         ...         0C0h-0C7h
AT DMA Controller 2             ...         0C0h-0DFh   ...
AT Clear/Reset 80287            ...         0F0h-0F1h   ...
AT 80287 Math Coprocessor       ...         0F8h-0FFh   ...
Joystick                        200h-20Fh   200h-207h   200h-207h
PC/XT Expansion Unit            210h-217h   ...         ...
AT Secondary Parallel Printer   ...         278h-27Fh   ...
Fourth Serial Port              2E8h-2EFh
Secondary Serial Port           2F8h-2FFh   2F8h-2FFh   ...
Prototype Card                  300h-31Fh   300h-31Fh   ...
Fixed Disk                      320h-32Fh   1F0h-1F8h   ...
Primary Parallel Printer        378h-37Fh   378h-37Fh   ...
PC/XT SDLC (Mainframe Comm)     380h-38Fh   ...         ...
AT Secondary Bisynch Comm       ...         380h-38Fh   ...
AT Primary Bisynch Comm         ...         3A0h-3AFh   ...
Monochrome Graphics Adapter     3B0h-3BFh   3B0h-3BFh   ...
Color Graphics Adapter          3D0h-3DFh   3D0h-3DFh   ...
Third Serial Port               3E8h-3EFh
Diskette Controller             3F0h-3F7h   3F0h-3F7h   0F0h-0FFh
Primary Serial Port             3F8h-3FFh   3F8h-3FFh   2F8h-2FFh

===============================================================================



Software Interrupt Vectors
--------------------------

00  Divide by Zero                        CPU
01  Single step                           CPU
02  Nonmaskable interrupt (NMI)           Memory Parity/Math Coprocessor
03  Breakpoint                            CPU
04  Overflow                              CPU
05  Bound range exceeded                  CPU (80286 and up)
06  Invalid instruction code              CPU
07  Coprocessor not present               CPU
08  Timer tick interrupt                  IRQ 0
09  Keyboard interrupt                    IRQ 1
0A  Cascade IRQ 08-0F for AT              IRQ 2
0B  Second RS-232C interrupt              IRQ 3
0C  First RS-232C interrupt               IRQ 4
0D  Second Parallel port Interrupt        IRQ 5
    Hard disk controller interrupt    
0E  Floppy diskette controller            IRQ 6
0F  First Parallel port interrupt         IRQ 7
10  Video services routine                BIOS support INT 10
11  Equipment inquiry service             BIOS support INT 11
12  Memory size inquiry service           BIOS support INT 12
13  Diskette I/O service                  BIOS support INT 13
14  RS-232C communication                 BIOS support INT 14
15  Cassette tape drive I/O               BIOS support INT 15
    Extended services
16  Keyboard buffer read/write            BIOS support INT 16
17  Parallel printer service              BIOS support INT 17
18  IBM BASIC Resident portion            IBM ROM BASIC
19  Bootstrap service                     BIOS support INT 18     check
1A  Time of day inquiry                   BIOS support INT 19
1B  Keyboard break (Ctrl-Break)           BIOS internal use
1C  Timer tick counter routine            BIOS internal use
1D  Address of video parameters table     BIOS internal use
1E  Address of diskette parameters table  BIOS internal use
1F  Video graphics                        EGA,VGA,ROM BIOS
20  Program termination                   DOS supports INT 20
21  MS-DOS service entry point            DOS supports INT 21
22  Program's terminate address           DOS internal use
23  Ctrl-Break exit address               DOS internal use
24  Fatal error handlers routine          DOS internal use
25  Absolute disk read                    DOS supports INT 25
26  Absolute disk write                   DOS supports INT 26
27  Terminate and stay resident           DOS supports INT 27
28  Available                             |
29  Available                             |
2A  Available                             |
2B  Available                             | INT HH
2C  Available                             |
2D  Available                             |
2E  Available                             |
2F  MS-DOS installable services           DOS internal use
30-3F Reserved by MS-DOS
40  Hard disk I/O                         BIOS from INT 13
41  Address of 1st hard disk parameters   BIOS internal use
    table
42  EGA VGA video services                EGA,VGA,ROM BIOS
43  Address of EGA VGA parameters table   EGA,VGA,ROM BIOS
44  Available
45  Available
46  Address of 2nd hard disk parameters   BIOS internal use
    table
47  Available
48  Available
49  Available
50  Clock alarm service                   BIOS internal use
51-5A Available                           INT HH
5B  Revector from INT19                   BIOS internal use
5C  IBM PC LAN network service            NETBIOS entry point
5D-66 Available
67  LIM EMS services entry point          EMS driver
68-6F Available
70  Real time clock interrupt             IRQ 8  (AT only)
71  Redirected to INT 9                   IRQ 9  (AT only)
72  Available on I/O slot                 IRQ 10 (AT only)
73  Available on I/O slot                 IRQ 11 (AT only)
74  Available on I/O slot                 IRQ 12 (AT only)
75  AT math coprocessor exception         IRQ 13 (AT only)
76  AT Hard disk controller interrupt     IRQ 14 (AT only)
77  Available on I/O slot                 IRQ 15 (AT only)
78-7F Available                           INT HH
80-F0 Reserved by IBM BASIC               IBM BASIC, internal use
F1-FF Available
===============================================================================
