ATI had a demo system running a pair of Radeon X1900s in CrossFire with a third X1900 card dedicated solely to physics processing. This configuration was appropriately referred to as the “meat stack,” and while it produced silky frame rates in a number of demos, it’s not the only Radeon configuration that will support GPU physics. In addition to supporting three-card configs, ATI will also allow a pair of its graphics cards to split rendering and physics between them. The graphics card dedicated to physics doesn’t even need to match the other graphics card(s) in the system; for example, it’s possible to run a high-end Radeon X1900 XTX crunching graphics alongside a more affordable Radeon X1600 series card for physics. In fact, ATI had a demo system set up with a pair of Radeon X1900s in CrossFire and a Radeon X1600 XT accelerating the Havok FX physics API.
With support for three-card configurations and no need to match cards used for graphics and physics, ATI looks to have the most flexible Havok FX acceleration implementation. ATI also claims to have a significant performance advantage when it comes to GPU-based physics acceleration, citing the Radeon X1000 series’ ample shader processing power, efficient dynamic branching, and fine-grained threading. Of course, the first games to use Havok FX aren’t expected until later this year. Havok FX isn’t exactly comparable to what Ageia’s doing with hardware physics acceleration, either; Havok FX is limited to “effects physics” that don’t affect gameplay, while Ageia’s PhysX PPU has no such limitation.