If memory doesn't stack for SLI, what happens to it?

[uhh3000]

I know that if I were to buy another 2gb gtx 670 and run SLI, I would have a total of 4 gb vram, but only 2gb effectively. What does that other 2gb in the other card do? Why doesn't it stack?

 

[noidea_77]

Because it has to be mirrored to the other card. Most of the memory is needed for textures and some program code for the shaders. The gpu needs that local to work effectively, that's why it's mirrored.

 

[Mousemonkey]

Because it has to be mirrored to the other card. Most of the memory is needed for textures and some program code for the shaders. The gpu needs that local to work effectively, that's why it's mirrored.

That pretty much sums it up, both cards have to hold the same information regardless of whether SFR or AFR is being used as the rendering method.

 

[uhh3000]

Oh okay, thanks. I was thinking at first that the two boards kinda merged into one in sli, but now I see

 

[uhh3000]

Best answer selected by uhh3000.