IBM Understanding the System Address Maps of Your Personal Computer

Appendix B. System address maps

The following charts represent how the hard disk stores different types of information. Address ranges and byte sizes are approximate.

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.

Table 32. System memory map

Address range	Address range (hex)	Size	Description
(decimal)
0–512 KB	00000–7FFFF	512 KB	Conventional
512–639 KB	80000–9FBFF	127 KB	Extended conventional
639–640 KB	9FC00–9FFFF	1 KB	Extended BIOS data
640–767 KB	A0000–BFFFF	128 KB	Dynamic video memory display
			cache
768–800 KB	C0000–C7FFFF	32 KB	Video ROM BIOS (shadowed)
800–896 KB	C8000–DFFFF	96 KB	PCI space, available to adapter
			ROMs
896 KB–1 MB	E0000–FFFFF	128 KB	System ROM BIOS (main memory
			shadowed)
1–16 MB	100000–FFFFFF	15 MB	PCI space
16–4096 MB	1000000–FFDFFFF	4080 MB	PCI space (positive decode)
4096–4120 MB	FFFE0000–FFFFFFFF	128 KB	System ROM BIOS

© Copyright IBM Corp. 2000 47