2x GTX 670s - Detected but no SLi

G

GenBanks

Gawd
Joined
Feb 26, 2008
Messages
634
The rig is the one in my sig.
They are both GTX 670s but they aren't identical, one has 2gb of vram and the other has 4gb. However, I was under the impression this didn't matter.

It everwhere seems to recognise that there are two graphics cards installed but for some reason the SLi options don't appear anywhere. I can only choose to make one of the graphics cards dedicated PhysX.

fcd03b6e-d283-4842-8e47-b7c7cd6c2c2c.jpg


Any ideas?
(the sli bridge connector is installed, I'm using the latest nvidia drivers and the BIOS of my motherboard is up to date.)
 
Looks like you have the monitor plugged into the second card? Plug it into the first one (the one closest to the processor). Otherwise, first thing I would try is putting the 2gb card in the slot where the 4gb is.
 
I've had this happen a few times, I just put the SLI bridge on and off a few times and suddenly it worked. Try using the other set of fingers or reversing the direction.
 
King Icewind said:
Looks like you have the monitor plugged into the second card? Plug it into the first one (the one closest to the processor). Otherwise, first thing I would try is putting the 2gb card in the slot where the 4gb is.
Click to expand...

Not sure why it's showing as being plugged into the second card, it's plugged into the top one (first slot). When I plug the monitor into the other card I get my desktop background without any icons or taskbar (as if it thinks it's a second monitor). They are in the correct PCI-e slots and show as working at x16 speed Gen2.

I tried switching the two around, but it didn't make any difference...

I've had this happen a few times, I just put the SLI bridge on and off a few times and suddenly it worked. Try using the other set of fingers or reversing the direction.
Click to expand...

Ok, I'll try this some more... but I've already tried changing it a few times to no avail.
 
I don't think you can SLI cards with different RAM sizes. You used to be able to, but not anymore.

Edit: Nvidia's official FAQ says you can, but you have to use something called Coolbits:

1. Open regedit.
2. Go to Computer/HKEY_LOCAL_MACHINE/SOFTWARE/NVIDIA Corporation/Gobal/NVTweak
3. Create two new strings called Coolbits and Coolbits64, with a value of 18 for both.
4. Restart.
 
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I have never SLIed cards with different RAM sizes, but I was under the impression it would work fine, except you would have only the lowest RAM available on the other card.
 
PiERiT said:
I don't think you can SLI cards with different RAM sizes. You used to be able to, but not anymore.

Edit: Nvidia's official FAQ says you can, but you have to use something called Coolbits:

1. Open regedit.
2. Go to Computer/HKEY_LOCAL_MACHINE/SOFTWARE/NVIDIA Corporation/Gobal/NVTweak
3. Create two new strings called Coolbits and Coolbits64, with a value of 18 for both.
4. Restart.
Click to expand...

Will this definitely work without messing up my machine? I've been googling coolbits and it seems like it used to work but it's no longer possible to do it with newer nvidia drivers...
 
GenBanks said:
Will this definitely work without messing up my machine? I've been googling coolbits and it seems like it used to work but it's no longer possible to do it with newer nvidia drivers...
Click to expand...

I can't say for certain, since I can't find much info on it either, but I highly doubt it'd mess up your machine. Worst case, your drivers would crash and you'd have to delete the values in safe mode.

Edit: According to an EVGA rep, Coolbits no longer works as of 310.90 drivers. Assuming that's true, you'd have to downgrade to that or buy a different card.
 
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PiERiT said:
I can't say for certain, since I can't find much info on it either, but I highly doubt it'd mess up your machine. Worst case, your drivers would crash and you'd have to delete the values in safe mode.

Edit: According to an EVGA rep, Coolbits no longer works as of 310.90 drivers. Assuming that's true, you'd have to downgrade to that or buy a different card.
Click to expand...

Well I gave the coolbits tweak a try it a try and SLi is now shown as being enabled in the nvidia control panel! Thanks PiERiT!

Now I'm going to check whether it has translated into better game performance...
 
Hm. Glad it worked.

Pretty crazy that there's zero solid info on this. Every time I read something, I read another thing that contradicts it.
 
Oops...
Unfortunately I need to retract my statement.
SLi was enabled but I wasn't able to play any games and I'd get frequent error messages and crashes.

I guess multi-gpu with different vram graphics cards isn't supported after all...
 
GenBanks said:
Oops...
Unfortunately I need to retract my statement.
SLi was enabled but I wasn't able to play any games and I'd get frequent error messages and crashes.

I guess multi-gpu with different vram graphics cards isn't supported after all...
Click to expand...

I always thought diff ram sizes wouldn't work. Different clock speeds on the other hand work fine. If you are running 1080p, sell the 4gb and put toward a 2gb!
 
Luckily the 4gb one isn't mine, I borrowed it from a friend to see the performance gains for myself.

I might get a second one anyway though, since I want to get the most out of my 120hz monitor!
 
SLI has never had an issue with different vram configurations before, so if it does that is a new change. Maybe the smaller amount needs to be in the primary position? I've SLI'd 1.5GB and 3GB 580's a while back and it had no issues at all.
 
Requirements: "...only the model and memory amounts have to match. For example, a GTX 580 with 1.5GB of memory could only be paired with another GTX 580 that has 1.5GB of memory, and a GTX 690 only with another GTX 690. Beyond that, manufacturers can be mixed (e.g. ASUS with MSI, EVGA with PNY,) clock speeds may vary (stock versus factory-overclocked,) the VGA BIOS for each card can be different, and no special drivers or software is required."

http://www.geforce.com/whats-new/guides/introduction-to-sli-technology-guide#4


From Nvidia: 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.

http://www.geforce.com/hardware/technology/sli/faq#c19
 
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