SLI with different VRAM

Cervarian

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Jan 1, 2014
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10,510
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Well, it seems I made an error when purchasing from Newegg and ordered a second GTX 680 to accompany my old one, but the new one has 2GB of VRAM where the old one has 4GB. For some reason, Newegg have forbid me from returning the product so now I am stuck trying to jury-rig it. I have spent hours searching, looking up, and trying software such as coolbits/NVTweak, but cannot seem to get them to work together.

To sum up: it seems to me, that Coolbits and NVTweak are rather out of date and don't work too well with a Windows 7 64x bit system. I have tried to go through the motions with them and am unable to make them appear in the control panel's display options or the Nvidia Control panel. I have made some headway however, and while I AM able to have the cards SLI properly in the Nvidia Control Panel, anytime I start an application I am locked into a black screen that constantly refreshes the source feed and am forced to shut down the computer.

Any information or other methods that would allow two GTX 680's with 2 and 4 GBs of VRAM to SLI with one another would be much appreciated.
 


Have you actually done this yourself without using Coolbits?

NVidia states:
"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."

*However, this FAQ is removed from the SLI list, so did they fix this in their drivers? Is Coolbits still required?
 

Cervarian

Honorable
Jan 1, 2014
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10,510
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Here, for a bit more clarity, here are the two cards in question.

1st card (had for over a year now): http://www.newegg.com/Product/Product.aspx?Item=N82E16814130794

2nd card (Just ordered): http://www.newegg.com/Product/Product.aspx?Item=N82E16814130853

I know, it was a pitiful mistake. But anyway, as you see, the first one is discontinued which kept me from ordering another of the same. Also, if it will help, my motherboard: http://www.newegg.com/Product/Product.aspx?Item=N82E16813157290

Everything else is standard: 16GB of RAM, SSD, i7 intel... As for the CoolBits registry trick, I am able to "Enable SLI" once I have ran the regedit and reboot. After the next step - changing the registry to allow additional options in display/Nvidia Control Panel - I am at a loss. It seems to me that some of the menus and UI for both the normal and Nvidia Control Panels are lost in translation from XP/2003 to Windows 7, causing no additional menus to appear or options to enable.

As I mentioned earlier, I am able to enable the SLI under the Nvidia Control Panel, but whenever I run a program is when things go awry. I have tested each card by itself, running multiple programs such as Witcher 2, Crysis, and even simple things such as FTL all without fault and they seem to be perfectly fine when by themselves, installed together, and banded with the SLI bridge. On that note: the computer and the Nvidia CP detect the cards, but it is only with the Registry edit from CoolBits that I have been able to make the option show. I have also applied the latest Nvidia drivers, used EVGA's Precision X to Sync the cards clocks, and tried the cards in multiple configurations on the motherboard, short of putting one of the two cards in the tertiary PCIe x16 slot which, in reality, only has 8 working bands/lanes. I have also scanned the ASRock BIOS and have been unable to find anything relating to SLI, making sure there is no "switch" I have to flip in there or on the board itself. I have considered a BIOS update... but am hesitant to do something that could cause irreparable harm to my computer.

I hope this additional information helps.
 
You could try contacting NVIDIA directly.

Another option is to try selling one of those cards, then get another one which is IDENTICAL or as close to possible for GPU frequency (and of course the same VRAM).

I recommend trying to sell the older, 4GB card, then buy a new 2GB model.
 

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