202 Intel
®
E7520 Memory Controller Hub (MCH) Datasheet
System Address Map
4.1.1 System Memory Spaces
The address ranges in this space are:
• DOSMEM 0_0000_0000 to 0_0009_FFFF
• MEM1_15 0_0010_0000 to 0_00EF_FFFF
• MAINMEM 0_0100_0000 to TOLM
• HIGHMEM 1_0000_0000 to 7_FFFF_FFFF
Note: Although the MCH can physically address up to 32 GB of DRAM memory, the addition of the high
PCI memory range may create an unusable range if the allocated range extends below 32 GB. The
MCH does not offer reclaim of this range when such overlap occurs, as supported processors are
limited to 36 address bits regardless.
Note: Inbound accesses are now supported for the Extended BIOS region from 0xE0000 through
0xEFFFF. The rest of the 640KB--1MB range remains unsupported for inbound DMA -- the MCH
will abort attempted accesses irrespective of PAM address access control settings.
These address ranges are always mapped to system memory, regardless of the system
configuration. The Top of Low Memory (TOLM) register provides a mechanism to carve memory
out of the MAINMEM segment for use by System Management Mode (SMM) hardware and
software, PCI add-in devices, and other functions. The address of the highest 128 MB quantity of
populated DRAM in the system is placed into the DRB7 register, which will match the Top of
Memory (TOM) register when both DIMM sparing and memory mirroring are disabled. For
systems with a total DRAM space and low PCI memory-mapped space of less than 4 GB, the value
in TOM will match that of the TOLM register. For other memory configurations, the two are
unlikely to be the same, since the PCI configuration portion of the BIOS software will program the
TOLM register to the maximum value that is less than 4 GB and also allows enough room for the
total memory space below 4 GB (LoPCI) allocated to populated PCI devices.
Figure 4-2. DOS Legacy Region
Upper, Lower,
Expansion Card BIOS
and Buffer Area
1MB
640 KB
768 KB0C0000h
0A0000h
Co n t ro l l e d by
PAM[6:0].
Monchrome Display
Adapter Space
Standard PCI/ISA
Video Memory
(SMM Memory)
0B8000h
0B0000h
736 KB
704 KB
Co n t ro l l e d by
VGA Enable and
MDA enable.
= DRAM
Key
= Optionally DRAM
