IBM 500 manual EBDA Memory Addresses, Memory Map

SurePOS 500 4846-XX5 Technical Reference

3.7EBDA Memory Addresses

The Extended BIOS Data Area (EBDA) starts at the segment pointed to by the contents of 40:0Eh.

Start Location	Length in bytes	Description	Comments
00h	1	Length of EBDA in KB
01h	32	Reserved
17h	1	Number of POST errors	not required
18h	5	POST error log	not required
22h	4	Mouse Driver Ptr	Int 74h
26h	1	Mouse flag byte 1	Int 74h
27h	1	Mouse flag byte 2	Int 74h
28h	8	Mouse data	Int 74h
30h	3d0h	Reserved	Reserved

3.8Memory Map

This section documents the default memory map. Note that add-in cards or changing CMOS Setup items may alter the memory map, particularly below 1 MB.

Memory Map with USB Legacy Support enabled (default)

Physical		Physical	Size	Description
Address Range
		Address Range (Hex)
(Dec)
0-639 KB		00000-9FC00	512 KB	Conventional DOS memory (size may decrease if booted
				via LAN)
639 KB		9FC00-9FFFF	1 KB	EBDA (Extended BIOS Data) moveable by Himem,
				memory managers
640-767 KB		A0000-BFFFF	128 KB	Legacy Video Buffer
768-831 KB		C0000-CFFFF	64 KB	Video BIOS ROM (shadowed)
832-863 KB		D0000-D7FFF	32 KB	USB Legacy Support
864-867 KB		D8000-D8FFF	4 KB	Network ROM boot loader
868-895 KB		D9000-DFFFF	28 KB	Free for EMM386
896 KB-959KB		E0000-EFFFF	64 KB	Free for EMM386
960KB – 1MB		F00000-FFFFFF	64KB	System ROM BIOS
1- 16 MB		100000-FFFFFF	15 MB	PCI/ISA Space
16 MB – 4095.5		1000000-FFF7FFFF	4079.5	OS, PCI adapter memory decode, etc.
MB			MB
4095.5 MB - 4096		FFF80000-FFFFFFF	512 KB	System ROM BIOS (ISA Bus)
MB
Memory Map with USB Legacy support disabled:
Physical	Physical		Size		Description
Address Range
	Address Range (Hex)
(Dec)
0-639 KB	00000-9FC00		512 KB		Conventional DOS memory (size may decrease if
					booted via LAN)
639 KB	9FC00-9FFFF		1 KB		EBDA (Extended BIOS Data) moveable by Himem,
					memory managers
640-767 KB	A0000-BFFFF		128 KB		Legacy Video Buffer

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