Yes and no. The GPU is responsible for the graphics and in a decent system with a good graphics, the CPU will offload the drawing to the GPU. It will also use the floating point processor in a decent graphics card to do some of its calculations. Obviously this usually means that a high level game will not need as powerful a processor. Unfortunately many modern games designers know this and use this feature to make their games more complex, thus wasting the advantages it gave. It is a bit like regularily relying on your fuel tank having a little in reserve and consistently using it, then wondering why you are stuck in the midle of nowhere when it really runs out.
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