Attila only showing 3gb VRAM. Have 2x 4gb video cards in sli

[gabrielscunha]

Hello all.

I have 2 770 PSY OC2 4gb working in SLI, but at the options page Attila only shows 3gb. Is there something I can do? Shouldn't it show 8gb? If there is some workaround, would it improve performance?

Thanks in advance!

[LestaT]

http://www.twcenter.net/forums/showt...izing-all-VRAM

I never use sli or xfire but I think using them does not double your vram but double (in theory) the performance so you'll only be seeing 4 gb (or 3.5 for 970) rather than 8 gb.

[SPARTAN VI]

^ that's correct.

Currently, simply using crossfire or SLI does not double/triple/quadruple your VRAM as all cards have to store the exact same frame data in VRAM to perform alternate frame rendering (AFR). If each card takes turns rendering a frame, then that means they all must have the same data in memory. Ex: Rendering a tree on frame 1 and frame 2. Both GPUs are 2GB and the frame data is 2GB (it's a very detailed tree, mkay). GPU1 must save all the frame data (geometry, textures, etc) to render frame 1 (i.e. 2GB), and GPU2 must also save the exact data to render frame 2 (i.e. the same 2GB). Both cards' VRAM are maxed out.

It's been discussed that Mantle (currently) and DX12 (eventually) allow for split frame rendering, where each card is responsible for its own half (or fraction) of rendering a frame, which would essentially mean they no longer have to store each other's frame data in memory. So eventually, having two cards with 4GB each will mean 8GB total of VRAM. Ex: Remember we're rendering that tree earlier? This time, GPU1 will take care of the first half of frame, so it only needs to store frame data for the half that its rendering (i.e. 1GB for the upper frame), and the other half of the frame for GPU2 (i.e. another 1GB for the lower frame). That leaves us with 2GB left over to play with; 1GB left unused on each card! Hurrah!

Currently with non-Mantle/DX12 APIs, we're limited to AFR, so having two 4GB cards means you only have 4GB of VRAM to play with.

That doesn't change the fact that Attila should be seeing the full 4GB on your GTX 770s. Take a look at this thread to fix it: http://www.twcenter.net/forums/showt...highlight=VRAM

[A Barbarian]

Most VRAM is actually used by textures, so it will stilll be very difficult to save a lot of shared VRAM in DX12 for CF/SLI solutions.