Intel D15343-003 manual System Memory Segments and Their Attributes, DOS Area 000000h-09FFFFh

Intel® 82854 GMCH System Address Map

Table 26.	System Memory Segments and Their Attributes
	System Memory	Attributes		Comments
	Segments
	000000H - 09FFFFH	Fixed - always mapped to main		0 to 640 kB – DOS Region
		DDR SDRAM
	0A0000H - 0BFFFFH	Mapped to Hub interface or IGD		Video Buffer (physical DDR SDRAM
		- configurable as SMM space		configurable as SMM space)
	0C0000H - 0C3FFFH	WE(Write Enable) RE (Read		Add-on BIOS
		Enable)
	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.

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.

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