is it possible to use two gpus for cycles and only one for gaming?

i couldn’t find any answer using google…

my question is : can i use two gpus for cycles rendering and only one of them for gaming?
i have ASUS P5Q pro motherboard and afaik i can put two gpu
currently i have gtx 260 and i want to buy gtx 660 - can i set this so when rendering with cycles gtx 260 is used for display and gtx 660 for computations? and can such a rig work for playing games in NON sli mode? like gtx 260 stays idle when game runs on gtx 660?

im not sure if this setup would be a mess but i hope this can work…?

GTX660 -> primary PCIe slot
GTX260 -> secondary PCIe slot

Make the GTX660 the primary card in windows.
You will not be able to activate SLI as the GPUs are different, nor would SLI do anything for cycles, and do not install the SLI bridge.

Games will launch on the primary screen using the 660, cycles should see both cards and be usable.

In case you don’t have 2 displays, you might have to connect a dummy-dvi dongle to the gtx260, as windows does not activate graphic cards without a screen, dunnow though how this is handled in CUDA.

And I don’t know how this works in Cycles, but in Octane it’s a bad idea to mix two GPUs with that much performance difference, as the slower card will hold the faster one back, not to mention that you can only use the memory amount of the smaller card for rendering.

I am also not certain if this even works, as both cards need a completely different render kernel as they use shader models which are, seen in graphic hardware terms, lightyears apart.

regarding power difference - will it matter when x260 is used only for display ?

I am not sure what you actually want as you’re pretty vague.

Case 1:
660+260 in Computer, screen connected to each.
660 primary display, 260 secondary display, Cycles only running on 660.
-> Games will run on primary display running on 660, no slowdown from 260.

Case 2:
660+260 in Computer, screen connected to each.
660 primary display, 260 secondary display, Cycles running on both cards.
-> Games will run on primary display running on 660, 260 is most likely to slow down Cycles, and you’ll only be able to use the smaller memory amount of both cards for rendering.

Case 3:
660+260 in Computer, screen connected to 660 only.
-> Makes no sense at all, the 260 is abysmal slow to use for cycles only, it’ll not be recognized by windows as active card without a display/dummy-dvi.

You also have to be aware that having the 260 in the system will slow down your gaming performance.
I don’t know the mainboards specs by heart, but IIRC it has PCIE x16 electrical but offers 2*PCIE x16.
If you plug in both cards, they share the electrical x16, running at x8 each.
While this is irrelevant for rendering with cycles as we’re talking nano- and milliseconds to load everything in the VRAM, you’ll have a noticable impact in gaming performance, especially with texture hungry games, streaming data.
For instance, if you turn around 180° in a game, you’ll have lagging most likely as the engines usually flush geometry/textures they don’t need and stream the newly needed ones to the device.

This will most likely also affect the OpenGL viewport performance of Blender. If it’s noticeable, no idea.

thank u for patience and help!