There are two modes for Nvidia’s PhysX :
- GPU accelerated Physics
- CPU only physics
Nedless to say Nvidia being Nvidia made it such that GPU acceleration only happens on Nvidia Graphic cards . For AMD graphic card users PhysX would run entirely on CPU which causes more bottle-necking .
There are also rumors that Nvidia purposefully botched the CPU only implementation of PhysX to make sure it runs poorly on CPU so that people are encouraged to buy Nvidia cards to get GPU accelerated physics