NVIDIA PhysX SDK is proprietary, multi-platform, realtime physics engine middleware. Middleware physics engines allow game developers to avoid writing their own code to handle the physics simulation, and focus on other aspects of the game.
While PhysX SDK is mostly used to calculate in-game physics on CPU, some games and applications are supporting enhanced hardware accelerated physics effects - running normally only if appropriate NVIDIA GPU is found the system. More details: NVIDIA PhysX Technology
