Using two different graphic cards of the same brand

Currently I have GeForce GTX 660 2GB, but I plan to upgrade to GTX 1060. Can I use both cards and somehow utilize the old card too for rendering in cycles? Or in any way for blender?

blender ‘should’ recognize all cards connected to your computer and you should be able to select which one (or both) to render on in the user prefs).

The only downside is that the 1060 will be significantly faster than the 660… as a result the tiles will finish way quicker on the 1060, leaving the question whether or not the 660 is worth rendering on in the first place.

…and that’s not the only downside.
When rendering on multiple cards, the card with the least amount of VRAM will determine how much (or rather: little) memory is available for rendering. The cards don’t share memory, so the scene has to fit into any card’s individual VRAM. And if one card can’t take it, the entire render will fail.

So, with a 2 GB 660 and a 6(?) GB 1060, you will only be able to use 2 GB max for rendering if you render on both.

Thanks for answers. Is it maybe possible to set one card for rendering and the other one (660) for interface, windows explorer and other programs? So I could do something else during rendering, because currently on one card interface is horribly lagging when I do rendering or set viewport shading to rendered.

Is it maybe possible to set one card for rendering and the other one (660) for interface …

Yes but the lower card must connected to the display.
I had a system with to different cards, performance wise, and set tiles to 3 or 6.
Faster card render 2 tiles and lower render 1 at the same time.

Cheers, mib