GTX 680 4Gb and SLI doubt

[wsarahan]

Hi guys

I have one doubt

If i get 2 GTX 680 with 4 Gb each considering that i`ll make tha SLI will i have 8GB or i have to consider just the primary card and i will only have 4Gb only with the SLI?

asking because i think i`ll get 2 680 and i need the 4GB one because i use 2560x1440 resolution

Thanks

 

[teaser]

No it wont double your video memory,you should be good with the 680 4 gig though at 2560x1440.........I have a vanilla evga 680 2 gig and game at 1920x1200,so the 4 gig should do you good

 

[Fokissed]

Each GPU has to work with it's own memory, and render (almost) identical frames. You'll have an effective 4GB VRAM with 2xGTX 680 SLI 4GB.

 

[wsarahan]

Each GPU has to work with it's own memory, and render (almost) identical frames. You'll have an effective 4GB VRAM with 2xGTX 680 SLI 4GB.

Thanks

Now i just need to know if it's enough to run games at 2560x1440

 

[deathengine]

ITS PLENTY. I have run 2gb versions with 3 screens at 5760x1080 and very few games run a memory bottleneck.

 

[Murissokah]

Its way more than enough for today's needs.

Getting a bit technical as to why 2x4GB is not 8GB:

The usual method for rendering with two cards is AFR (alternate frame rendering), in which one frame is rendered in one card and the next on the other, working up to twice as fast as a single one.

If each card has to render a full frame, each one needs to load all the content releated with that frame in its buffer. Since there is no means to share the buffer between the cards (a very fast bus between them would be needed, and the controllers would have to address a bus twice as large), the data loaded into the buffer is pretty much duplicated.

 

[Fokissed]

Thanks

Now i just need to know if it's enough to run games at 2560x1440

Should be. I have a GTX 680 4GB and the most memory I've seen games use is ~1800MB VRAM. This is at 1080p. If it were completely correlated with the framebuffer size (it's not), then you would use 78% more VRAM.

Realistically I doubt you'll see it hit 3GB usage very often.