Intel S975XBX2 - Workstation Board Motherboard, Specification, Page: 47 / 102

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2 Technical Reference
What This Chapter Contains
2.1 Memory Resources .......................................................................... 47
2.2 DMA Channels................................................................................. 49
2.3 Fixed I/O Map ................................................................................. 50
2.4 PCI Configuration Space Map ............................................................ 51
2.5 Interrupts ...................................................................................... 52
2.6 PCI Conventional Interrupt Routing Map ............................................. 53
2.7 Connectors ..................................................................................... 54
2.8 Jumper Block .................................................................................. 67
2.9 Mechanical Considerations ................................................................ 68
2.10 Electrical Considerations................................................................... 70
2.11 Thermal Considerations .................................................................... 72
2.12 Reliability ....................................................................................... 74
2.13 Environmental ................................................................................ 75
2.1 Memory Resources
2.1.1 Addressable Memory
The board utilizes 8 GB of addressable system memory. Typically the address space
that is allocated for PCI Conventional bus add-in cards, PCI Express configuration
space, BIOS (SPI Flash device), and chipset overhead resides above the top of DRAM
(total system memory). On a system that has 8 GB of system memory installed, it is
not possible to use all of the installed memory due to system address space being
allocated for other system critical functions. These functions include the following:
• BIOS/SPI Flash device (8 Mbit)
• Local APIC (19 MB)
• Digital Media Interface (40 MB)
• Front side bus interrupts (17 MB)
• PCI Express configuration space (256 MB)
• MCH base address registers, internal graphics ranges, PCI Express ports (up to
512 MB)
• Memory-mapped I/O that is dynamically allocated for PCI Conventional and PCI
Express add-in cards
The board provides the capability to reclaim the physical memory overlapped by the
memory mapped I/O logical address space. The board remaps physical memory from
the top of usable DRAM boundary to the 4 GB boundary to an equivalent sized logical
address range located just above the 4 GB boundary. Figure 14 shows a schematic of