I have seen some similar threads, but my setup is slightly different. I too am seeing that BOINC only appears to recognize and use a single card, even though I have 2 in SLI. I was debating buying a 3rd, but not if the apps can't use it. Here's what I have:

Asus P6T6 WS Revolution motherboard
Two GTX 260's in slots 1 and 5 as instructed by the manual for two way SLI.
I did verify in the nVidia control panel that SLI is enabled and non-BOINC apps do see it.

However, here is what BOINC reports:
1/30/2009 6:06:15 PM||Starting BOINC client version 6.6.3 for windows_x86_64
1/30/2009 6:06:15 PM||log flags: task, file_xfer, sched_ops
1/30/2009 6:06:15 PM||Libraries: libcurl/7.19.2 OpenSSL/0.9.8i zlib/1.2.3
1/30/2009 6:06:15 PM||Data directory: C:\ProgramData\BOINC
1/30/2009 6:06:15 PM||Running under account pharrg
1/30/2009 6:06:15 PM||Processor: 8 GenuineIntel Intel(R) Core(TM) i7 CPU 920 @ 2.67GHz [Intel64 Family 6 Model 26 Stepping 4]
1/30/2009 6:06:15 PM||Processor features: fpu tsc pae nx sse sse2 pni
1/30/2009 6:06:15 PM||OS: Microsoft Windows Vista: Home Premium x64 Editon, Service Pack 1, (06.00.6001.00)
1/30/2009 6:06:15 PM||Memory: 5.99 GB physical, 12.09 GB virtual
1/30/2009 6:06:15 PM||Disk: 233.81 GB total, 148.92 GB free
1/30/2009 6:06:15 PM||Local time is UTC -7 hours
1/30/2009 6:06:15 PM||Not using a proxy
1/30/2009 6:06:16 PM||CUDA device: GeForce GTX 260 (896MB, est. 96GFLOPS)

Should I report this on the BOINC forum, or any suggestions? Thanks.

Please try to run it with SLI disabled.

I can try that just to see if it works in a while. However, just as the problem I'm having with the fans, I'm not going to want to enable and disable SLI everytime I start and stop BOINC to run a game or something.

I'm not going to want to enable and disable SLI everytime I start and stop BOINC to run a game or something.

Hmmm... sounds like a nice little utility for someone to program... and icon in the system try to quickly right click and enable or disable SLI.

To me it seems to be simple enough IMHO:

(1) right mouse click on the desktop
(2) click on NVIDIA control panel
(3) disable multi-GPU-mode
(4) confirm ...

Thanks. That worked. I wonder how many people think they're using 2, 3, or even 4 CUDA cards and are really just using 1 since they have SLI enabled for game performance and such.

I think that'd be a great option to add to the BOINC core client (and have posted to them as well), to add a check box that would tell BOINC to automatically issue commands to disable SLI when doing CUDA, though probably it should also only do that when in screensaver mode. This way, it doesn't impact games and such if they set BOINC to continue working when the computer is in use. Otherwise, on multi-card machines, you'll miss out on a lot of processing speed if the user doesn't take the time to go into the control panel everytime which, to an extent, defeats the whole purpose of using CUDA.

I don't understand why CUDA can't use all cores in SLI mode. Games are written to do that. They in fact are the driving factor for having SLI technology. Is nVidia just behind on enabling their own SLI technology in CUDA?

Anyway, thanks again. I'll disable SLI whenever I'm not playing games for now.