Rendering on CPU vs GPU how to enable CUDA and performance on older system I am on an older system, Windows 7, it is built on an Asus Sabertooth X58, I am low on RAM @ 4GB , CPU is an Intel I7 950 a Quad core @ 3.07 GHz, graphics card is a Geforce GTX 460 , boot drive an OCZ vertex solid state.
what I am wondering is about using CUDA, and if my card is compatible, when I click on CUDA in preferences/system it tells me 'no compatible GPU's found for path tracing Cycles will render on CPU'. Now I realize that message seems clear but I have to wonder because I use TMPGEnc Video Mastering Works 5 and it uses CUDA on my system I do video processing so when I assembled my computer I was sure to pick a CUDA graphics card.
I don't expect CUDA rendering would outpace my CPU, but the thing is I have a second GTX 460 sitting in a box so I am wondering IF the card is compatible and I was to reinstall that second card and I was to use that card just to render I would get slower render times, but my system would not be bogged down with the process during the render?
when I took the second GPU out it was because the video software was causing issues, it was years ago so I dont remember exactly but it had to do with SLI issues and using CUDA to process video. I ended up just taking the card out to avoid the hassles, but that issue back then has me wondering if Blender is telling me no compatible GPU's because of the old issue ( software being grabby about CUDA...)
Your card is way too old, below the minimum specs needed for the current versions of blender.
From the manual
https://docs.blender.org/manual/en/latest/render/cycles/gpu_rendering.html

CUDA
CUDA requires graphics cards with compute capability 3.0 and higher. To make sure your GPU is supported, see the list of Nvidia graphics cards with the compute capabilities and supported graphics cards. CUDA GPU rendering is supported on Windows, macOS, and Linux.

Check the minimum requirements here too:
https://www.blender.org/download/requirements/
You can try using older versions (2.79 or below) which might work, but know that you might not get any benefits for using CUDA at all.
Also blender does not work with SLI.