ATI has a running system with 3 X1900XTX cards running with 2 running in Crossfire mode and one doing the physics calculations in one of the private rooms and there are several Havok FX demos installed to show the power of physics calculations on ATi cards. The system is running off Conroe 2.66GHz and Intel D975XBX board on x8 /x8 /x4 PCI-E configurations as well as a 1KW PCPowerCooling PSU.
There is also another system running with 2 x X1900XTX cards and 1 x X1600XT card on ATi RD600 chipset on x8 /x8 /x4 PCI-E configurations. It is also possible to run on mismatched cards for eg. one X1900XTX paired up with one X1600 or X1300 card with the former doing the rendering and the latter doing the physics.
VR-Zone has the opportunity to talk to the VP of the ATI desktop graphics dept and learn more about this new technology. He revealed that the X1900XTX delivers 9x better performance than the AGEIA PhysX card and X1600XT is twice faster. The speed of physics calculation depends on two main factors; core clock and parallel pipelines and the reason why GPU is much faster than CPU in physics calculations is due to the fact that GPU is capable of data parallel processing. Apart of Havok, ATi is currently in talks with AGEIA to include their API as well.