I have 2 8600gt gpu's and am using cuda. It seems only one gpu is being used using sli or not. (temp goes up only 1 gpu) start up preferances show 1 gpu. Is this normal or am I configurew wrong ?

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Do both of them have at least 256MB of memory?
Are they both cards? Or are they embedded? Did you install the CUDA enabling drivers for both of them?

How many cards/chips does CUDA-Z say there are and what does it say about memory available on them and their compute capability?

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Both are cards and have 256mb I'm not sure if both have cuda they went in at the same time any updates were with both cards running.I'm not sure what cuda-z is telling me (total global memory 256) Should it show 2 cards seperate in summary?

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I think it should, else you should be able to select which card to look at with the bottom drop down menu. If it's only showing you 256MB global memory, I'm not sure but it sounds like you have two cards with each 128MB of memory.

Let's try GPU-Z. http://www.techpowerup.com/gpuz/

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Try re-installing drivers for both cards (via device manager)
Although programs may report them using the same driver if they weren't both updated then you will only have 1 card used.

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Each card has 256mb

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Installed latest drivers to each card thru device manager. No change. On seti start up messages coprocessor 8600gt(1). Card temp. shows 1 card approx 12 deg. c warmer so I'm sure only 1 card is being used. Should I reinstall 6.4.5 and if so Unstall it first?

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I am having the exact same issue (even have the exact same cards!). It appears that BOINC is viewing the SLI cards as one oversized card that is only uses the first portion of. Is there anything that can be done to automatically have CUDA break these two cards into individuals so it can run 2 WUs at once?

Also, one thing that I noticed... in non-SLI mode, it will do 2 WUs at the same time, but split them up on the 1st video card and the second stays idle. (according to what I observed with temp changes)

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I am having the exact same issue (even have the exact same cards!). It appears that BOINC is viewing the SLI cards as one oversized card that is only uses the first portion of. Is there anything that can be done to automatically have CUDA break these two cards into individuals so it can run 2 WUs at once?

Also, one thing that I noticed... in non-SLI mode, it will do 2 WUs at the same time, but split them up on the 1st video card and the second stays idle. (according to what I observed with temp changes)

SLI mode will make the cards appear as one. Turning SLI off should have 2 separate tasks running (1 on each)

Were both tasks showing progress?

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Installed latest drivers to each card thru device manager. No change. On seti start up messages coprocessor 8600gt(1). Card temp. shows 1 card approx 12 deg. c warmer so I'm sure only 1 card is being used. Should I reinstall 6.4.5 and if so Unstall it first?

I see your using vista...I believe that at folding@home they had to put a monitor/dummy monitor and extend the desktop onto the second card to get it to work (in non sli mode)

Worth a shot (if you have the stuff available)

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I show 1 task either in SLI or not. Using EVGA in SLI I show 2 gpu"s #1 runs approx. 54 deg c #2 runs approx 67 deg c. Non SLI it shows 1 gpu and runs hot approx 77 deg c. So it looks like 1 gpu is doing most of the work in SLI and all of the work in non SLI. Have about 25% computation errors also. Show gpu failure and recovery occasionaly.

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They were showing progress, but they were both going half the speed that it was before... but only one card was heating up.

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