Well This is quite complicated. Yes it is the "processors" of the video card.. If you have a dirrect comparison the Cuda cores are better 1 to 1 but that is not the way to compair ATI VS NVIDIA b/c if you look at this last gen the GTX 580 has 512 CUDA cores but the 7970 has 2048 AT Streem cores.. so you cannot compair them as these two cards perform very close to one another... Yes you want a card with more but dont buy a card based on the core count if you got an ATI card with 512 cores you would be very dissapointed but if you got an Nvidia card with 512 Cores you should be very happy.. The cores are used to proccess video to the screen or do calculations for software that uses CUDA or Open CL.