My SCENIC/ESPRIMO or CELSIUS workstation has 4GB of memory but Windows XP (32bit) / BIOS only shows 3GB (or less), why is this?
In 4GB configurations the visible memory may be reduced down to 3.0GB or lower depending on your system configuration. 32-bit architecture imposes some limitations on the size of the address space and on the amount of usable memory. The system memory is not the only memory in a computer. Some devices have memory too, therefore the physical address space is not used solely for system memory but is shared with other devices. Typically the physical address space that is allocated for PCI add-in cards, AGP/PCI Express aperture, BIOS (firmware hub), and chipset overhead, resides above the system memory. In lower memory configurations therefore there is no overlap. However in for example 4GB configs when both ranges overlap, the devices have priority. So the overlapping part of the system memory gets no physical addresses assigned. Hence windows reports the system memory as being lower by the over-lapping amount. For more detailed information on this issue, please read the white paper.
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