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

System Address MapSystem Address Map 4The processor in an 865G chipset system supports 4 GB of addressable memory space and 64KB+3 of addressable I/O space. There is a programmable memory address space under the1-MB region that is divided into regions that can be individually controlled with programmableattributes (e.g., disable, read/write, write only, or read only). Attribute programming is described inChapter 3. This section focuses on how the memory space is partitioned and the use of the separatememory regions.The Pentium 4 processor family supports addressing of memory ranges larger than 4 GB. TheGMCH claims any processor access over 4 GB and terminates the transaction without forwardingit to the hub interface or AGP (discarding the data terminates writes). For reads, the GMCH returnsall zeros on the host bus. Note that the 865G chipset platform does not support the PCI DualAddress Cycle Mechanism; therefore, it does not allow addressing of greater than 4 GB on eitherthe hub interface or AGP interface.In the following sections, it is assumed that all of the compatibility memory ranges reside on thehub interface/PCI. The exception to this rule is VGA ranges that may be mapped to AGP or to theIGD. In the absence of more specific references, cycle descriptions referencing PCI should beinterpreted as the hub interface/PCI, while cycle descriptions referencing AGP are related to theAGP bus.The 865G chipset memory map includes a number of programmable ranges.Note:All of these ranges must be unique and non-overlapping. There are no hardware interlocks toprevent problems in the case of overlapping ranges. Accesses to overlapped ranges may produceindeterminate results.4.1 System Memory Address RangesThe 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 space in hardware. It isthe BIOS or system designers responsibility to limit memory population so that adequatePCI, AGP, High BIOS, and APIC memory space can be allocated. Figure 9 provides asimplified system memory address map. Figure 10 provides additional details on mapping specificmemory regions as defined and supported by the GMCH.Intel ® 82865G/82865GV GMCH Datasheet 139