I will try to include the main points

EVGA 780i MB
8800GT in top PCI-E slot
8400GS in the bottom slot
Vista 64 bit sees both cards just fine so do the newest Nvidia drivers
tried BOINC 6.4.5 and 6.6.2 and neither sees the 8400GS only the 8800GT
Suggestions?

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I have it figured out. I had nothing, in terms of monitors, connected to the 8400GS. For some reason that made a difference. I moved my second monitor over to the 8400GS and now it shows up in BOINC. I have no idea why this is the case but it seems if you have multiple cards in and your not running them SLI you have to have something connected to it for BOINC to see it and use it.

FYI, with two monitors connected to different cards Vista dream scenes don't work.

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Answer by David Anderson, lead developer of BOINC:

The latest client handles multiple GPUs, but not quite correctly:
it picks the fastest one, then acts as if all the GPUs are that kind.

The main problem with this is memory: e.g.,
if the faster board has >= 256MB but the slower board has < 256MB,
BOINC will try to run the SETI@home/CUDA app on the slower board.

We'll fix this at some point, but probably not for a couple of months.

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