What's the deal with SLI VRAM?

[jfarrugia98]

So i'm thinking of investing into another GTX 970 for my gaming rig, and i'm aware that putting two cards in SLI doesn't double the memory.. But why? If we think about it, what is happening to that extra 4 Gigabytes of memory? Does it just sit there and do nothing? Or does the computer only register it as 4GB, but in actual fact run as 8GB? Really confused, if this is the case then what is the actual benefit of SLI? Thanks.

 

[Darkbreeze]

The benefit is this:

Most of the games operate in AFR (alternate frame rendering). The first card renders one full frame and then the next card renders the next frame and so on.


This is why it's better to SLI card models that have more memory, like a 4GB GTX 960 rather than a 4GB GTX 960 (Not that I recommend buying two GTX 960's rather than a single bigger card), or an 8GB 290x rather than a 4GB model. That way, although only one cards memory gets used, you still have an ample amount regardless that the core resources for two cards are in play.


Often many cards don't even use their full memory unless a very specific set of circumstances is met, or if the card is being used in a dual card configuration. It would seem that a lot of this is going to change though with the advent of the upcoming DirectX 12.