Intel D15343-003 manual Extended System Memory Area, Expansion Area 0C0000h-0DFFFFh

Intel® 82854 Graphics Memory Controller Hub (GMCH)

Monochrome Display Adapter (MDA) Range (0B0000h - 0B7FFFh)

Monochrome Display Adapter ranges is accessible when the Intel® 854 Chipset is strapped into Native Graphics mode. Legacy support requires the ability to have a second graphics controller (monochrome) in the system. Accesses in the standard VGA range are forwarded to IGD and the Hub interface (depending on configuration bits). Since the monochrome adapter may be mapped to anyone of these devices, the GMCH must decode cycles in the MDA range and forward them either to IGD or to Hub interface. This capability is controlled by a VGA steering bits and the legacy configuration bit (MDAP bit). In addition to the system memory range B0000h to B7FFFh, the GMCH decodes IO cycles at 3B4h, 3B5h, 3B8h, 3B9h, 3BAh, and 3BFh and forwards them to either the IGD or the Hub interface.

Expansion Area (0C0000h-0DFFFFh)

This 128-kByte ISA Expansion region is divided into eight, 16-kB segments. Each segment can be assigned one of four Read/Write states: read-only, write-only, read/write, or disabled. Typically, these blocks are mapped through GMCH and are subtractively decoded to ISA space. System memory that is disabled is not remapped.

Extended System BIOS Area (0E0000h-0EFFFFh)

This 64-kByte area is divided into four, 16-kB segments. Each segment can be assigned independent read and write attributes so it can be mapped either to main DDR SDRAM or to Hub interface. Typically, this area is used for RAM or ROM. System memory segments that are disabled are not remapped elsewhere.

System BIOS Area (0F0000h-0FFFFFh)

This area is a single 64-kB segment. This segment can be assigned Read and Write attributes. It is by default (after Reset) Read/Write disabled and cycles are forwarded to Hub interface. By manipulating the Read/Write attributes, the GMCH can "shadow" BIOS into the main DDR SDRAM. When disabled, this segment is not remapped.

5.3Extended System Memory Area

This system memory area covers 100000h (1 MB) to FFFFFFFFh (4 GB-1) address range and it is divided into the following regions:

•Main system memory from 1 MB to the top of system memory.

•PCI Memory space from the top of system memory to 4 GB with two specific ranges.

•APIC Configuration Space from FEC0_0000h (4 GB-20 MB) to FECF_FFFFh (4 GB-19 MB - 1) and FEE0_0000h (4 GB-18 MB) to FEEF_FFFFh (4 GB-17 MB-1).

•High BIOS area from 4 GB to 4 GB - 2 MB

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