Why do some PhysX demos only run on one CPU core?
PhysX fully supports applications which are multi-threaded to leverage multiple CPU cores. Some single-feature PhysX demos consist of only one type of physics body which runs more efficiently on a single CPU core. If the same demo was part of a more complete game environment, there would be multiple PhysX objects and active game and rendering threads, so the game would leverage more than one CPU core more efficiently. Improving the way individual PhysX objects can be efficiently spread over multi-processors is being actively researched and developed.