SurePOS 500 4846-XX5 Technical Reference
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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
