Unlike other approaches, Havok FX handles physics computations directly on the GPU, allowing it to calculate and render object movement with minimal readback to the CPU. However, Havok FX is limited to what's referred to as "effect physics," or physics that don't affect gameplay. Havok prefers to keep gameplay physics on the CPU, leaving Havok FX with the physics calculations necessary for visual effects and other eye candy. Fortunately, modern GPUs apparently do a pretty good job of crunching those types of physics calculations. In one example, NVIDIA claims Havok FX running on a pair of GeForce 7900 GTX graphics cards in SLI is more than ten times faster than software physics calculations running on a Pentium Extreme Edition 955.
Havok FX isn't finished yet, but NVIDIA says developers are quite happy about the prospect of implementing a technology that can take advantage of an existing installed base. Indeed, Havok FX shouldn't suffer from the potential chicken-and-egg scenario facing Ageia's PhysX PPU, whose not-yet-existent installed base might discourage developers from implementing the technology. That dilemma may limit the number of supported games, which could slow PhysX adoption. Havok FX shouldn't have that problem, because by the time it's released, there should be plenty of users with compatible GeForce 6 and 7-series graphics cards. In fact, Havok's web site indicates Havok FX was designed for Shader Model 3-class GPUs, so it's entirely possible it will work with select Radeons, as well.
NVIDIA will be demoing Havok FX on its graphics hardware at the Games Developer Conference this week. Havok FX is currently being used by a few select developers, with a wider release planned for the summer.