Appendix B. System Address Maps
Appendix B. System Address Maps
System Memory Map
The first 640 KB of system board RAM is mapped starting at address hex 0000000. A 256-byte area and
a 1 KB area of this RAM are reserved for BIOS data areas. Memory can be mapped differently if POST
detects an error.
Input/Output Address Map
The following figure lists resource assignments for the I/O address map. Any addresses that are not
shown are reserved.
Figure 46. System Memory Map
Address Range (decimal)
Address Range (hex)
Size
Description
0 K – 512 K
00000–7FFFF
512 KB
Conventional
512 K – 639 K
80000–9FBFF
127 KB
Extended conventional
639 K – 640 K
9FC00–9FFFF
1 KB
Extended BIOS data
640 K – 800 K
A0000–C7FFF
160 KB
Video memory and BIOS
800 K – 896 K
C8000–DFFFF
96 KB
PCI/ISA space, available to
adapter ROMs
896 K – 928 K
E0000–E7FFF
32 KB
POST/BIOS(sys ROM,
shadowed in maintenance)
928 K – 992 K
F0000–FFFFF
64 KB
POST/BIOS (sys ROM,
shadowed in maintenance)
1024 K – 262144 K
100000–10000000
255 MB
Extended
Figure 47 (Page 1 of 3). I/O Address Map
Address (Hex)
Size
Description
0000–000F
16 bytes
DMA 1
0020–0021
2 bytes
Interrupt controller 1
002E–002F
2 bytes
I/O controller configuration registers
0040–0043
4 bytes
Counter/timer 1
0048–004B
4 bytes
Counter/timer 2
0060
1 byte
Keyboard controller byte - reset IRQ
0061
1 byte
NMI, speaker control
0064
1 byte
Keyboard controller, CMD/STAT byte
0070, bit 7
1 bit
Enable NMI
0070, bits 6—0
7 bits
Real time clock address
0071
1 byte
Real time clock data
0072—0077
6 bytes
Real time clock addresses and data
0078
1 byte
Reserved - system board configuration
0079
1 byte
Reserved - system board configuration
0080–008F
16 bytes
DMA page registers
00A0–00A1
2 bytes
Interrupt controller 2
Copyright IBM Corp. September 1998
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