JG82855GMESL7VN Datasheet, PDF (67/213 Pages) Intel Corporation – Intel® 855GM/855GME Chipset Graphics and Memory Controller Hub (GMCH)

Register Description
R
4.8.14
GGC – GMCH Graphics Control Register (Device 0)
Address Offset:
Default Value:
Access:
Size:
52–53h
0030h
Read/Write
16 bits
Bit
15:7
6:4
3:2
1
0
Description
Reserved
Graphics Mode Select (GMS): This field is used to select the amount of Main system memory that is
pre-allocated to support the Internal Graphics Device in VGA (non-linear) and Native (linear) modes. The
BIOS ensures that system memory is pre-allocated only when Internal Graphics is enabled.
000 = No system memory pre-allocated. Device #2 (IGD) does not claim VGA cycles (Memory and I/O),
and the Sub-Class Code field within Device #2 Function #0 Class Code register is 80.
001 = DVMT (UMA) mode, 1 MB of system memory pre-allocated for frame buffer.
010 = DVMT (UMA) mode, 4 MB of system memory pre-allocated for frame buffer.
011 = DVMT (UMA) mode, 8 MB of system memory pre-allocated for frame buffer.
100 = DVMT (UMA) mode, 16 MB of system memory pre-allocated for frame buffer.
101 = DVMT (UMA) mode, 32 MB of system memory pre-allocated for frame buffer.
All other combinations reserved.
Reserved
IGD VGA Disable (IVD):
1 = Disable. Device #2 (IGD) does not claim VGA Memory and I/O Mem cycles, and the Sub-Class
Code field within Device #2 Function #0 Class Code register is 80.
0 = Enable. Device #2 (IGD) claims VGA Memory and I/O cycles, the Sub-Class Code within Device #2
Class Code register is 00.
Reserved
Datasheet
67