Intel 925 Data Sheet - Page 162

System Address Map R 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 nonaddressable; 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 FFFF_FFFFh Flash 4 GB Maximum Contains programmable windows, ICH6/PCI ranges. APIC PCI Memory Range (Optional) TSEG (1 MB / 2 MB / 8 MB, optional) TOLUD Main Memory 0100_000h 00F0_000h 0010_000h 0h ISA Hole (optional) Main Memory DOS Compatibility Memory 16 MB 15 MB 1 MB 0 MB Main_Mem_Addr 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 Intel® 82925X/82925XE MCH Datasheet