whats does GPU and CPU mean?

well there is a big diffrence,

CPU stands for Central processing unit

The Cpu is centred in the middle of your computer's motherboard, this is what speeds your computer up. strong Cpu's are good for renderers like:

yafaray

blender internal

GPU stands for Graphics processing unit

The Gpu is basicly the graphics card but this can be linked up to renderers using software like Cuda drivers, renderers like:

Octane

Hypershot

these programs both use the Gpu and the Cpu. using both processing units, rendertime is rapidly decreased so rendering takes nearly no time at all! it becomes so fast you can rotate around your 3d model in realtime rendering!!

Gpu with Cpu is a whole new stage of rendering power!