SurePOS 500 4846-XX5 Technical Reference
Page 26 of 63
3.7 EBDA
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
3.8 Memory
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
Address Range
(Dec)
Physical
Address Range (Hex)
Size Description
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
MB
1000000-FFF7FFFF
4079.5
MB
OS, PCI adapter memory decode, etc.
4095.5 MB - 4096
MB
FFF80000-FFFFFFF
512 KB
System ROM BIOS (ISA Bus)
Memory Map with USB Legacy support disabled:
Physical
Address Range
(Dec)
Physical
Address Range (Hex)
Size Description
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
