Main Memory Address Range (1 Mb To Tolud); Isa Hole (15 Mb-16 Mb); Figure 9-3. Main Memory Address Range - Intel 925 - Pentium D 925 3.0GHz 800MHz 4MB-Cache Socket 775 CPU Datasheet

System Address Map
9.2

Main Memory Address Range (1 MB to TOLUD)

This address range extends from 1 MB to the top of physical memory that is permitted to be
accessible by the MCH (as programmed by BIOS). All accesses to addresses within this range
will be forwarded by the MCH to the main memory unless they fall into the optional TSEG or
optional ISA Hole.
The MCH provides a maximum main memory address decode space of 4 GB. The MCH does not
remap APIC or PCI Express memory space. This means that as the amount of physical memory
populated in the system reaches 4 GB, there will be physical memory that exists, yet non-
addressable; therefore, this memory is unusable by the system.
The MCH does not limit main memory address space in hardware.

Figure 9-3. Main Memory Address Range

9.2.1 ISA Hole (15 MB–16 MB)
BIOS can create a hole at 15 MB–16 MB. Accesses within this hole are forwarded to the DMI.
The range of physical main memory disabled by opening the hole is not remapped to the top of
the memory; that physical main memory space is not accessible. This 15 MB–16 MB hole is an
optionally enabled ISA hole.
162
FFFF_FFFFh
Flash
APIC
Contains
programmable
PCI Memory Range
windows, ICH6/PCI
ranges.
(Optional)
TSEG (1 MB / 2 MB /
8 MB, optional)
Main Memory
0100_000h
ISA Hole (optional)
00F0_000h
Main Memory
0010_000h
DOS Compatibility
Memory
0h
4 GB Maximum
TOLUD
16 MB
15 MB
1 MB
0 MB
Main_Mem_Addr
®
Intel 82925X/82925XE MCH Datasheet
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