PhysX is a proprietary realtime physics engine middleware SDK. It was developed by Ageia with the purchase of ETH Zurich spin-off NovodeX in 2004. Ageia was acquired by Nvidia in February 2008.
The term PhysX can also refer to the PPU expansion card designed by Ageia to accelerate PhysX-enabled video games.
Video games supporting hardware acceleration by PhysX can be accelerated by either a PhysX PPU or a CUDA-enabled GeForce GPU (if it has at least 256MB of dedicated VRAM), thus offloading physics calculations from the CPU, allowing it to perform other tasks instead. In theory this should result in a smoother gaming experience and allow additional visual effects.
Middleware physics engines allow game developers to avoid writing their own code to handle the complex physics interactions possible in modern games. PhysX is one of the handful of physics engines used in the large majority of today's games.
The PhysX engine and SDK are available for Microsoft Windows, Mac OS X, Linux, PlayStation 3, Xbox 360 and the Wii. The PhysX SDK is provided to developers for free for both commercial and non-commercial use on Windows. For Linux, OSX and Android platforms the PhysX SDK is free for educational and non-commercial use.