I couldn't figure out why suddenly after updating my nVidia drivers, I couldn't get BOINC to see both CUDA cards and process two CUDA work units.

I was reading elsewhere that starting with nVidia driver version 190.38 which has CUDA 2.3, the system will now only see 2 CUDA devices with SLI enabled, so you should now be able to enable SLI and leave it on all the time, even when running BOINC, just the opposite of the older drivers. In fact, you MUST enable SLI or BOINC will only see 1 device now.

I checked my BOINC Manager, and sure enough, it was only showing one CUDA device. I exited BOINC, enabled SLI, and restarted BOINC, and then it showed two (I have two GTX 260's) and started processing two CUDA work units at the same time again.

So, just to make things more confusing for everyone, it appears that the rule for SLI flips for anyone who runs the newer 190.38 or higher drivers. I've now recreated this on a friends machine as well.

I'm running GpuGrid in a PC with two GPUs and I dissabled SLI and it works as it did before the new drivers. The problem I found with SLI being activated is that when a WU fails in one GPU the other fails too, so I deactivated SLI. May be it was only a fortuitous case, but...

The PC runs under Windows Vista Home Premium 32 bits.

I am indeend running a 64bit version of Vista. You would think they'd make the drivers behave the same under all OS's, but then again, that would be too simple. Perhaps people just need to see how things behave on whatever they run. For example, on mine, I haven't seen tandem failures such as you have on your 32bit system. I'm glad too since I must turn on SLI or BOINC only sees one CUDA device under the new drivers. Seems that at least on some systems, we don't have to turn SLI off anymore, but I guess it's not true on all systems. Maybe the version of BOINC someone is running makes a difference on how it interacts with the new drivers. I'm running 6.6.38. Anyway, it seems to be fast and stable on mine.

Nice to see this post here, as I was just about to search for a thread where I can comment, that I am able to utilize both of my 275's with SLI bridge and SLI enabled in Nvidia settings, no need to disable it like some old instructions say. This is very nice when the computer is used also for gaming.

My rig: i7, 2xGTX275, 190.38 driver, Win7x64

Boinc for me recognises both GPUs with SLI on or off (vista 64) with 190.62, but with SLI on the drivers stop responding and GPUgrid crashes. The problem is when I toggle SLI on or off it also crashes GPUgrid.

Ok still getting compute errors with SLI off but not quite as often. Will try 190.38 and hope

Installed yesterday 3 x GTX 260 into a Win Server 2008 SP2, under BOINC 6.10.0 & recommended 190.38 drivers. After few rearrangements (moved one GTX to another PCI-E slot) system was recognize all GPU's. SLI was not enabled. 11 WU's was successfully completed in that config. I think, that the problem isn't in SLI, but in the way, how BOINC detect GPU's, installed in different PCI-E slots ( probably, the way of IRQ or PCI-E X lines distribution \ management by MoBo BIOS).

Regards,

Jet