As simble as it sounds. If I were to SLi 2 (for example) GTX 760 GPUs, would the extra GPUs just be used for aditional processing power or can the video memory in each extra card also be utilized?
No, the total VRAM is only equal to that of one card. At least from my understanding, the memory must be mirrored on both cards. Basically, if you SLI'd two 2GB 760s, you'd still only have 2GB of VRAM.
^ This is correct
And this is where cards like the 690, 7990, r9295x2, and other two in one cards come in handy...:D
On the dual GPU cards they just add the video memory of the two cards. So even though the 295x2 has 8 GB, it really has 4 GB per gpu, so it's still effectively 4 GB.
If I understood correctly the second card's memory is a mirror (exact copy) of the first card and the first GPU renders the even frames while the other renders the uneven frames.
(If I'm talking utter bollocks here please correct me)
Nvidia SLI FAQ-
you got it somewhat but sometime the gpus have trouble timing these actions and you end up getting a major lag ever once in a while. whether In SLI or X-fire, they have the same problem, but AMD and Nvidia are working on it