Datasheet

System Address Map
R
164 Datasheet
Table 37. System Memory Segments and Their Attributes
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, AGP
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
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/MCH.
Legacy VGA Ranges (0A0000h-0BFFFFh)
The legacy 128-kB VGA memory range 0A0000h-0BFFFFh (VGA Frame Buffer) can be mapped
to IGD (Device #2), to AGP/PCI1 (Device#1) and to the hub interface depending on the
programming of the VGA steering bits. Priority for VGA mapping is constant in that the
GMCH/MCH always decodes internally mapped devices first. Internal to the GMCH/MCH,
decode precedence is always given to IGD. The GMCH/MCH always positively decodes
internally mapped devices, namely the IGD and the AGP/PCI1. Subsequent decoding of regions
mapped to the AGP/PCI1 or 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. AGP and hub interface originated
cycles to enabled SMM space are not allowed and are considered to be to the video buffer area if