How does Sli/crossfire work?

[logan]

So....im not that knowledgeable  with GPU's...iv only had 2....a GT 430...and a GTX 970 ...but i next plan to have 2 GTX 980 Ti's......(or a highend card....when i have the money,...they might have cards twice as goon as 980 Ti's by then)

 

but i don't know...if i have to enable the games to use both GPU's....or if all games automatically use both....i know some games are only 1 GPU compatible...and some work worse with multiple GPU's, cause their poorly ported/optimized 

[Muz]

[Godlygamer23]

SLI and Crossfire require explicit enabling in the respective driver control panel. After that, games will follow a set profile given by NVIDIA or AMD if it has one. If you do buy an NVIDIA card and want SLI down the line, you will need to make sure(at least as of right now) you have an SLI bridge handy.

[KarateHottie93]

Well pretty much every single game from the past decade supports SLI. The only two triple A titles I can think of that don't are CoD4 and I think the frst Crysis. Not like any modern card would need it for them anyways though.

[Acquire]

Ideally all you have to do on your end is go into the Nvidia control panel and turn on SLI.  It's a driver level synchronization between the GPUs to spread the rendering work.  The driver will search for a profile that matches with the game that it is trying to render, if none are found it defaults to just using your primary GPU for rendering (as if you didn't have SLI).  Most games of high marketing prowess will have an SLI profile ready at launch or a bit after, but it's not guaranteed.  Shadow of Mordor took a while to get one.  In those cases someone usually comes up with a custom profile you can apply really easily using a simple tool (Nvidia Inspector).  For all other games you'll be stuck with just one GPU.  Ultimately, you're at the mercy of Nvidia to get profiles into the driver.  They have a pretty good track record for getting them out on time though.