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[shawkie]

I have a PC with 4GB running Windows XP 32-bit. I am fairly sure that at one point approx 3.5GB of this was accessible in Windows but now only approx 2.5GB is accessible. I think the change happened when I installed a second 7950GT in the system. I know that Windows XP 32-bit is limited to a 4GB address space. Does the memory on the graphics card somehow get deducted from this 4GB address space? If I swapped the 7950GTs for 7950GX2s (which have 1GB RAM each instead of 512MB) would I lose another 1GB? Is there some other explanation for what I'm seeing?

[phoenxhwk]

The IO space of many of your expansion cards will end up eating into the overall 32-bit physical address space on your machine. The word physical is important here. Win32 can talk to 4GB worth of HARDWARE addresses, which includes all your IO devices and DRAM. There is a PCI/PCI-E option for a card to remap itself into addresses higher than 4GB (thus freeing them up), but I haven't seen much hardware that actually does this. Check your BIOS for a "pci remap" option - I think that's what they usually call it.

Note that while this will impact the amount of physical RAM you can access, it will NOT mess with your virtual memory. Thus a process can still allocate up to 3GB of memory, regardless of how much RAM your computer is reporting. Sure it will be slow, but it will at least work.

[john bell]

[Perumaal]