Physics acceleration: the Next Big Thing™?
 

However, the GPU does not feed very much data back to the CPU as a result of its physics calculations, which means that nothing that the GPU produces in the way of physics simulation can really affect gameplay. So you couldn't use the GPU to simulate the partial demolition of a structure that's holding some NPCs, because the CPU wouldn't know enough about the results. The simulated demolition would go from the GPU straight to the framebuffer and onto the screen, like so many water or particle effects, but nobody would tell the actual game code running on the CPU where the large chunks of debris (fallen beams, pieces of wall, the inevitable barrels and crates) had fallen and where the new gap in the wall appeared.

In contrast to GPU-based "physics acceleration," the PhysX co-processor actually collaborates with the CPU to affect gameplay.