Seems I have suddenly got an issue. Had 3 GPU's running for a few days no probs. Added a Dummy VGA from another rig to get all 4 GPU's and as soon as I start BOINCManager. BSOD.

No matter if I put 2x Monitor on Port 1 on each card and the VGA dummies on Port 2(both cards lights go blue as expected) or shuffle everything around. Oh and SLi is off by the way.

Running FurMark all is well and showing 4 GPU's used. Runs to completion.

I know the dummy works its been on an ATI for a while with no issues and if I put it back on the ATI all is well.

Anyone else tried all 4 GPU's under Vista?

Now granted I was using 6.6.15 and have gone to 6.6.20 but same issue with both. I'm not wanting to go all the way back to 6.4.5 but heh that's my next shot if noone has a better idea.

It's Vista Ultimate 32 SP1 by the way with driver 182.08.

Don't know about Vista much in that I am still an XP shop ... But have had not troubles with 2 GTX 295 cards which look to windows as 4 GPUs ...

I *DID* have troubles with drivers and BSOD with the Nvidia tools till I tried the last drop ...

The only point I can suggest is to go to 6.5.0 instead of 6.4.5 ...

Okay the 4th GPU has entered the building.

After I taught myself CUDA I wrote my own program to enumerate the CUDA drivers present and was seeing 3 even though the nVidia control panel and the MMC device panel was showing 4. So it's not BOINC Manager.

I deinstalled all the nVidia drivers, rebooted and checked in the registry at

Hkey_Local_Machine\Hardware\DeviceMap\Video

to see what I had. There were 3 devices Video0, Video1 and Video2 present which were all standard VGA drivers. I then installed Forceware 185.68 and rebooted.

I now had 10 devices in the registry. I navigated down to

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Video\

and looked to see what was present. Here we see a list of registry keys like

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Video\(GPU ID)\0000

where there is a key for each GPU. I searched the list and for each GPU e.g.

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Video\{D82C4D9A-396A-4292-A538-A8F8F22FFEB5}\0000\Settings field (where {D82C4D9A-396A-4292-A538-A8F8F22FFEB5} is a GPU id)

and looked for the words NVIDIA GeForce GTX 295.

I presumed (luckily correctly) that the 1st GPUID with those words i nthe Settings field had the monitor on it. To the following 3 GPU's I added the following registry keys:-

DisplayLessPolicy DWORD 1
LimitVideoPresentSources DWORD 1

at the

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Video\(GPU ID)\0000

level in the registry tree and rebooted.

Now I only have 2 monitors showing in the nVidia control panel as having my desktop on them but my own CUDA program shows 4 GPUS. I fired up BOINC Manager which still displays that it found only 3 (due to the string length being exceeded I expect) but I have 4 running GPUS.