Reply 20 of 37, by Falcosoft
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agent_x007 wrote on 2020-03-05, 17:26:red-ray wrote on 2020-03-04, 18:14:agent_x007 wrote on 2020-03-04, 17:21:While Titan X(M) "takes" 512MB
No it doesn't and I can't see how the screen shots you posted indicate it does. The prefetch area is 288 MB so there is no way it uses 512 MB!
Well, when I swap GPU from Titan Black to Titan X(M), my available RAM drops to 2,94GB (can be seen both in task manager and under System information), and when I swap back to Titan Black I get 3,44GB back again.
When get to PCIe with XP again, I will test this with Your program under XP.
According to your report your Titan X must have the starting address of its address space at 0xC0000000 while your Titan Black at 0xE0000000. You can check this even in Device Manger. Yet most likely the occupied address space is the same (namely 256MB at 0xC0000000-0xCFFFFFFF and 0xE000000-0xEFFFFFFF respectively and some other smaller auxiliary regions above these addresses). The smaller usable memory is due to 32-bit Windows could only use continuous address space for system memory only up to the first address occupied by any PCI devices .
The interesting thing is this starting address is not strictly tied to either occupied address space or onboard VRAM size. I have an older PC with an ATI card that has only 128 MB VRAM yet has its LFB region at 0xC0000000-0xC7FFFFFF. So it also occupies only 128MB PCI address space but since its starting address is at 0xC0000000 with 32-bit windows the maximum available RAM is only 3GB. In the same PC an NVIDIA card with 256MB onboard RAM has its LFB region at 0xD0000000-0xDFFFFFFF. So it occupied 256MB address space (more than the ATI card with only 128MB) yet with 32-bit windows the maximum available RAM is 3.25GB since the starting address is at 0xD0000000.
