Processor Configuration Registers
Figure 2-2. DOS Legacy Address Range
1 MB
000F_FFFFh
000F_0000h
000E_FFFFh
000E_0000h
000D_FFFFh
System BIOS (Upper)
64 KB
960 KB
Extended System BIOS (Lower)
64 KB (16KBx4)
896 KB
768 KB
640 KB
Expansion Area
128 KB (16KBx8)
000C_0000h
000B_FFFFh
Legacy Video Area
(SMM Memory)
128 KB
000A_0000h
0009_FFFFh
DOS Area
0000_0000h
2.3.1.1
2.3.1.2
DOS Range (0h–9_FFFFh)
The DOS area is 640 KB (0000_0000h–0009_FFFFh) in size and is always mapped to
the main memory controlled by the memory controller.
Legacy Video Area (A_0000h–B_FFFFh)
The legacy 128 KB VGA memory range, frame buffer, (000A_0000h–000B_FFFFh) can
be mapped to IGD (Device 2), to PCI Express (Device 1 or Device 6), and/or to the DMI
Interface. The appropriate mapping depends on which devices are enabled and the
programming of the VGA steering bits. Based on the VGA steering bits, priority for VGA
mapping is constant. The processor always decodes internally mapped devices first.
Non-SMM-mode processor accesses to this range are considered to be to the Video
Buffer Area as described above.
The processor always positively decodes internally mapped devices, namely the IGD
and PCI Express. Subsequent decoding of regions mapped to PCI Express or the DMI
Interface depends on the Legacy VGA configuration bits (VGA Enable & MDAP). This
region is also the default for SMM space.
20
Datasheet, Volume 2
INTEL [ INTEL ]
