"Before showing you the results of our tests, let¿s first discuss the uses the developers of the game had put the CPU to. So, from the numerous interviews of John Carmack, id Software¿s Technical Director, at various Internet sites it seems that skinning and shadows are the CPU¿s main responsibility in Doom 3. That is, the CPU calculates the positions of the characters¿ ¿skins¿ as they move between certain key points. This approach helps to animate the characters as well as render their facial expressions.

Evidently, the realization of dynamic shadows is thus better implemented using the CPU resources, too. That¿s why Doom 3 requires an assiduous CPU to run smoothly, as besides skinning and shadow generation the CPU has to solve the traditional problems of any game like monsters¿ AI, the physics of the game scene and tangent space transformations, necessary for a correct depiction of the game events on the screen."