Intel® 865G/865GV Chipset Datasheet - download.intel.nl - Intel

System Address Map4.3 Extended Memory AreaThis memory area covers the 1 MB to 4 GB–1 (100000h–FFFFFFFFh) address range and isdivided into the following regions:• Main system SDRAM memory from 1 MB to the Top of Memory; maximum of 4-GBSDRAM.• AGP or PCI Memory space from the Top of Memory to 4 GB, with two specific ranges:— APIC Configuration Space from FEC0_0000h (4 GB–20 MB) to FECF_FFFFh andFEE0_0000h to FEEF_FFFFh— High BIOS area from 4 GB to 4 GB – 2 MBMain System Memory Address Range (0010_0000h to Top of Main Memory)The address range from 1 MB to the top of system memory is mapped to system memory addressrange controlled by the GMCH. The Top of Main Memory (TOMM) is limited to 4-GB SDRAM.All accesses to addresses within this range will be forwarded by the GMCH to system memoryunless a hole in this range is created using the fixed hole as controlled by the FDHC register.Accesses within this hole are forwarded to the hub interface.The GMCH provides a maximum system memory address decode space of 4 GB. The GMCH doesnot remap APIC memory space. The GMCH does not limit system memory address space inhardware.4.3.1 15 MB–16 MB WindowA hole can be created at 15 MB–16 MB as controlled by the fixed hole enable (FDHC register) inDevice 0 space. Accesses within this hole are forwarded to the hub interface. The range of physicalSDRAM memory disabled by opening the hole is not remapped to the Top of the memory – thatphysical SDRAM space is not accessible. This 15-MB–16-MB hole is an optionally enabled ISAhole. Video accelerators originally used this hole. There is no inherent BIOS request for the15-MB–16-MB hole.Intel ® 82865G/82865GV GMCH Datasheet 143