Help me understand SLI a little better when it comes to RAM

[Arishok N7]

So I'm going to get another GTX 670ftw. I have the 2GB version in my system right now. When I get the other one, will that give me 4GBs to use, or still 2GB's? Example, if something requires 3GB's of GPU RAM, could SLI 670's do it?

 

[Jameson Clark]

Sli gpus only have as much memory as the gpu with the least on it, so you will still only have 2gb

 

[Hazle]

nope. doesn't work that way. two 2GB 670's in SLI still equates to 2GB of vram. if you SLI a 2GB 670 + 4GB 670, you're only getting 2GB of vram. only way you're getting more vram in SLI if you SLI two 4GB cards.

 

[Pinhedd]

So I'm going to get another GTX 670ftw. I have the 2GB version in my system right now. When I get the other one, will that give me 4GBs to use, or still 2GB's? Example, if something requires 3GB's of GPU RAM, could SLI 670's do it?

You may not be able to SLI them at all. Last I checked SLI requires all member GPUs to have the same amount of onboard memory. There was a modded driver that did allow GPUs with different amounts of memory to be used in SLI, but it would be constrained to the smallest amount. I'm not sure if the drivers have been updated to support this officially.

You may install and run the two separate cards with different amounts of memory and use them to drive different displays independently or run CUDA/OpenCL code to your heart's content but unless NVidia has relaxed the memory restriction on SLI you will not be able to use them in an SLI configuration to render the same game.

 

[JUICEhunter]

Here is the issue:

670SLI is fast, to the point where you are like "My fps are good, I can turn the settings up all the way" higher texture/aa use more VRAM, so although you have the speed for the highest settings, those same high settings max out 2gb VRAM and the card has to add and remove textures when 2gb is reached which causes stutters. The 4gb cards are better for SLI but in single card performance the extra VRAM doesn't make a difference as a single card can't max new games anyway.

You can force FXAA and lower ultra to high and that will shave off some VRAM usage and as long as you don't hit the 2gb limit with your settings your FPS will always be very high for a long time and you'd only be lowering settings to save VRAM not because your setup isn't fast enough which means you'll be killing games with low aa high settings on for a really long time.

Edit: If you're killing a game with 90 FPS on 'high' settings you can go up to 'very high' or 'ultra' although your 2gb GPU's may have to work harder which lowers FPS, you'll have a little leeway as long as you don't dip below 60fps or else you'll have to turn something down.

 

[bystander]

As has been said, you'll still effectively have 2Gb of VRAM and both cards must have the same amount. If they do not have the same amount, they have a program called Coolbits which will allow you to neuter the card with more VRAM so they are the same. Coolbits is just a registry edit program to make Windows think the card has less VRAM than it has. Last I checked, even though it was very old, it still works.

As far as needing more than 2Gb, it will be extremely rare to need more than 2Gb of VRAM, unless you are playing at 4k or use excessive AA (like SSAA or MSAAx8/x16. Pretty much no game needs more than 2Gb at 1080p, but there are a couple exceptions and the list may grow in time. The new Wolfenstein and Titanfall have texture options will will need more than 2GB to use. Turn the textures down, and it'll work perfectly find. This may become more common in the future, but if you have a 2Gb card now, it is not worth upgrading it over that.