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82854 GMCH System Address Map
D15343-003 113
Table 26. System Memory Segments and Their Attributes
DOS Area (000000h-09FFFFh)
The DOS area is 640 kB in size and is always mapped to the main system memory controlled by
the GMCH.
Legacy VGA Ranges (0A0000h-0BFFFFh)
Legacy VGA ranges is accessible when the Intel
®
82854 GMCH is strapped into Native Graphics
mode. The legacy 128-kB VGA memory range A0000h-BFFFFh (VGA Frame Buffer) can be
mapped to IGD (Device #2) and to the Hub interface depending on the programming of the VGA
steering bits. Priority for VGA mapping is constant in that the GMCH always decodes internally
mapped devices first. Internal to the GMCH, decode precedence is always given to IGD. The
GMCH always positively decodes internally mapped devices, namely the IGD. Subsequent
decoding of regions mapped to the Hub interface depends on the Legacy VGA configurations bits
(VGA Enable and MDAP). This region is also the default for SMM space.
Compatible SMRAM Address Range (0A0000h-0BFFFFh)
When compatible SMM space is enabled, SMM-mode CPU accesses to this range are routed to
physical DDR SDRAM at this address. Non-SMM-mode CPU accesses to this range are
considered to be to the video buffer area as described above. Hub interface originated cycles to
enabled SMM space are not allowed and are considered to be to the video buffer area.
System Memory
Segments
Attributes Comments
000000H - 09FFFFH Fixed - always mapped to main
DDR SDRAM
0 to 640 kB – DOS Region
0A0000H - 0BFFFFH Mapped to Hub interface or IGD
- configurable as SMM space
Video Buffer (physical DDR SDRAM
configurable as SMM space)
0C0000H - 0C3FFFH WE(Write Enable) RE (Read
Enable)
Add-on BIOS
0C4000H - 0C7FFFH WE RE Add-on BIOS
0C8000H - 0CBFFFH WE RE Add-on BIOS
0CC000H - 0CFFFFH WE RE Add-on BIOS
0D0000H - 0D3FFFH WE RE Add-on BIOS
0D4000H - 0D7FFFH WE RE Add-on BIOS
0D8000H - 0DBFFFH WE RE Add-on BIOS
0DC000H - 0DFFFFH WE RE Add-on BIOS
0E0000H - 0E3FFFH WE RE BIOS Extension
0E4000H - 0E7FFFH WE RE BIOS Extension
0E8000H - 0EBFFFH WE RE BIOS Extension
0EC000H - 0EFFFFH WE RE BIOS Extension
0F0000H - 0FFFFFH WE RE BIOS Area