QUOTE(oodini @ 07/27/07, 05:24 PM) [snapback]270521[/snapback]
Does interactive rendering (the one run with the clap icon) use all the CPUs ?
Well it doesn't use cpu at all, but thats the short answer real answer is that: In order for the gpu (you can have 1 2, or even 16 of these however) to render the image, the dg needs to be solved. Now dg is solved by the cpu. Now piror to maya 8.5 EVERYTHING in this step was single cpu, however the biggest upgrade in maya 8.5 was the fact that they multithreaded some of the nodes so maya 8.5 uses the second node occasionally. It is not whoever so easy to make guis work fully threaded. If you hve 4 then they will stand still.
So: the bottom line is unless you know computers very well, and i mean very well indeed and change the way you work, then the second processor will be 99% of the time idle.
NOW what you must learn is that the computer you use is a farm, while this slows memory bandwidth down a tad you can always test render stuff in the background (such as making swatches for each attribute combination with 0.1 units increment in some series so you can optimize the values fast when you go render). Or solve those cost effective calculations you need in a hour or so.