SLI with different cards?

Luck100

I currently have a self-built gaming PC with an EVGA gtx 670 ftw card. Thinking about adding a second card for SLI. How well does it work if the two cards don't match exactly? Most likely scenarios would be a used gtx 670 (but not necessarily EVGA ftw) or possibly a 660ti. Has anybody tried this? I think I can get a pretty good deal getting the second card used, but requiring an exact match makes it difficult.

The motherboard and power supply will support up to 3-way SLI so no worries there.

BloodBath

I'm pretty sure you can't mix nvidia cards in sli. It would have to be another 670.

U_Fig

As far as I know you can mix the different cards as long as both are GTX 670 like a stock card and say an EVGA ftw card should work

Luck100

Thanks BloodBath. I just went to NVidia's website and it says the same. It also recommends using cards with the same amount of memory. Apparently it's ok to mix cards from different vendors if you use drivers versioned 180 or later.

So, to refine my question: has anybody tried mixing two different version of the same card number? Like two gtx 670s, but one from EVGA and one from Asus. Or EVGA gtx 670 FTW + EVGA gtx 670 (not FTW). I'm quite sure it works, but perhaps there is great chance of stuttering or other glitches?

Details from NVidia FAQs:
http://www.geforce.com/hardware/technology/sli/faq#c16

Can I mix and match graphics cards that have different GPUs?
No. For example, an XXXGT cannot be paired with a XXXGTX in an SLI configuration.

Can I mix and match graphics cards from different manufacturers?
Using 180 or later graphics drivers, NVIDIA graphics cards from different manufacturers can be used together in an SLI configuration. For example, a GeForce XXXGT from manufacturer ABC can be matched with a GeForce XXXGT from manufacturer XYZ.

Can I mix and match graphics cards if one of them is overclocked by the manufacturer?
Yes. A GeForce XXXX GTX that is overclocked can be mixed with a standard clocked GeForce XXXX GTX.

Can I mix and match graphics cards with different sizes of memory?
When purchasing a second graphics card, you should try to match the memory size so that you are ensured full value and performance from your purchase. However, while it is not recommended, NVIDIA does offer the flexibility to run graphics cards with different sized memory by using CoolBits. Using CoolBits (value set to 18), you can force both of the cards to use the lower of the two memory sizes and operate them together in SLI mode. When dissimilar memory sizes are enabled to work together using CoolBits, the effective memory size for each card becomes the smaller of the memory sizes.

Serephucus

You can use any card you like, a long as it has the same core. So for example, a 660 Ti could be coupled with another 660 Ti with different clocks, memory size, cooler, and from a different manufacturer, and would still work.

The thing I'm not sure about is that the 670 FTW is essentially a crippled 680. It uses the same PCB, it just has a couple of SMUs disabled, and lower clocks, but it uses the same power delivery circuitry. I'd imagine though that it would still be seen by the drivers as a 670. Download GPU-Z and the like, make sure it's detected correctly, and you'll be good to pick up whatever 670 you like.

I know from experience that different manufacturer cards will work (I was running Zotac, and I think MSI or something 580s in SLI with no problems for a while)

deconduo

Serephucus wrote: »

You can use any card you like, a long as it has the same core. So for example, a 660 Ti could be coupled with another 660 Ti with different clocks, memory size, cooler, and from a different manufacturer, and would still work.

The thing I'm not sure about is that the 670 FTW is essentially a crippled 680. It uses the same PCB, it just has a couple of SMUs disabled, and lower clocks, but it uses the same power delivery circuitry. I'd imagine though that it would still be seen by the drivers as a 670. Download GPU-Z and the like, make sure it's detected correctly, and you'll be good to pick up whatever 670 you like.

I know from experience that different manufacturer cards will work (I was running Zotac, and I think MSI or something 580s in SLI with no problems for a while)

As far as I know, its a lot of hassle to mix NVidia cards in SLI, even in a case like that where one card is essentially just a locked down version of another. AMD cards tend to be a bit easier to deal with, but its still not recommended, as the better performing card will be throttled to the speed of the worse one.

Similarly if you are mixing cards of different speeds/memory they'll both be dropped to the speed/memory of the lowest card. So if you have a 900MHz 2GB card and an 850MHz 4GB card, they'll both run as 850MHz 2GB cards (unless you overclock them)

Serephucus

deconduo wrote: »

Similarly if you are mixing cards of different speeds/memory they'll both be dropped to the speed/memory of the lowest card. So if you have a 900MHz 2GB card and an 850MHz 4GB card, they'll both run as 850MHz 2GB cards (unless you overclock them)

That's actually only half true. The framebuffer will default to the lowest card, because the data has to be mirrored, but the clock speeds can be completely different, and they'll still work. Since both cards are working to render the same frame, the faster card will just get assigned a higher proportion of each frame to render to compensate for the extra speed.

deconduo

Serephucus wrote: »

That's actually only half true. The framebuffer will default to the lowest card, because the data has to be mirrored, but the clock speeds can be completely different, and they'll still work. Since both cards are working to render the same frame, the faster card will just get assigned a higher proportion of each frame to render to compensate for the extra speed.

Interesting, I didn't realise it was actually possible to do that.

Edit: It seems only SLI is able to do that, for crossfire they will be forced to run at the same clockspeeds.

Serephucus

Yeah, it was in a driver quite a while back. NVIDIA does a wonderful job of not mentioning a lot of cool things in their drivers. This was introduced back around the time of the GTX 285, to give you an idea.

Luck100

Thanks guys, this has been very educational!