| BIOS must reserve some address space below 4GB for PCI devices such as RAID controllers, SCSI controllers, NICs, etc. RAID controllers in particular may request and be given 256MB each. This is address space that would normally be occupied by RAM, but instead is used by PCI devices.
RAM addresses start at 0 and grow up. PCI device addresses start at 4GB and grow down. As long as there is no overlap, the OS will see all available RAM and make use of it. If there is overlap, the PCI devices win, and that RAM is not made available to the OS.
This is working as designed per PCI, BIOS, and system chipset specifications.
Matt_Domsch |
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