What happens to CPU when using GPU to render?

Hello blender artists, I was considering to purchase new computer system and I wanted to know what CPU does in cycles when the rendering is on GPU because it will affect my computer spec. I’ve searched in google but all I could’ve found were the comparison of cpu rendering and gpu rendering. So if you know, please tell me. Thank you:):):):slight_smile:

See http://www.blenderartists.org/forum/showthread.php?299844-Cycles-does-the-cpu-and-ram-even-matter

thank you sooo much