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Register Description
D15343-003 63
Table 21. PAM Registers and Associated System Memory Segments
For details on overall system address mapping scheme see the Address Decoding section of this
document.
DOS Application Area (00000h-9FFFh)
The DOS area is 640 kB in size and it is further divided into two parts. The 512-kB area at 0 to
7FFFFh is always mapped to the main system memory controlled by the GMCH, while the 128-kB
address range from 080000 to 09FFFFh can be mapped to PCI0 or to main DDR SDRAM. By
default this range is mapped to main system memory and can be declared as a main system
memory hole (accesses forwarded to PCI0) via GMCH's FDHC Configuration register.
Video Buffer Area (A0000h-BFFFFh)
Attribute Bits do not control this 128-kB area. The Host-initiated cycles in this region are always
forwarded to either PCI0 or PCI2 unless this range is accessed in SMM mode. Routing of accesses
is controlled by the Legacy VGA Control Mechanism of the "Virtual" PCI-PCI Bridge Device
embedded within the GMCH.
This area can be programmed as SMM area via the SMRAM register. When the GMCH is strapped
in other mode, or when used as an SMM space, this range can not be accessed from the Hub
interface.
Expansion Area (C0000h-DFFFFh)
This 128-kB area is divided into eight 16-kB segments that can be assigned with different attributes
via PAM Control register as defined in Figure 4 and Table 21.
PAM Reg Attribute Bits System Memory Segment Comments Offset
PAM0[3:0]
Reserved
59h
PAM0[7:4] R R WE RE 0F0000h–0FFFFFh BIOS Area 59h
PAM1[3:0] R R WE RE 0C0000h–0C3FFFh ISA Add-on BIOS 5Ah
PAM1[7:4] R R WE RE 0C4000h–0C7FFFh ISA Add-on BIOS 5Ah
PAM2[3:0] R R WE RE 0C8000h–0CBFFFh ISA Add-on BIOS 5Bh
PAM2[7:4] R R WE RE 0CC000h–0CFFFFh ISA Add-on BIOS 5Bh
PAM3[3:0] R R WE RE 0D0000h–0D3FFFh ISA Add-on BIOS 5Ch
PAM3[7:4] R R WE RE 0D4000h–0D7FFFh ISA Add-on BIOS 5Ch
PAM4[3:0] R R WE RE 0D8000h–0DBFFFh ISA Add-on BIOS 5Dh
PAM4[7:4] R R WE RE 0DC000h–0DFFFFh ISA Add-on BIOS 5Dh
PAM5[3:0] R R WE RE 0E0000h–0E3FFFh BIOS Extension 5Eh
PAM5[7:4] R R WE RE 0E4000h–0E7FFFh BIOS Extension 5Eh
PAM6[3:0] R R WE RE 0E8000h–0EBFFFh BIOS Extension 5Fh
PAM6[7:4] R R WE RE 0EC000h–0EFFFFh BIOS Extension 5Fh