ATI utilizes a 8x1 pixel shader path, with one path at 8 bits. Nvidia, on the other hand, uses a 4x2 path with two paths each 4 bits wide. Currently, any game using PS 2.0 with the FX cards is only accessing shaders at 4x1, due to driver and DX9b limitations (we will see DX9c soon, mark my words) and so, the DX9 games and 45:23 driver is effectively ignoring the second PS 2.0 path. The preview 51:75 driver alleviates this problem, enabling the full second path for use in the game as much as possible before any update to DX9 is implemented to allow true dual channels as intended by its design. We see these HL2 benchmark results now because HL2 is seriously dependant on pixel shaders in their current form and it is singly responsible for the framerate discrepancies. The fix coming with the Det.50 should bring the numbers in line with ATI's, and additionally, the updated DX9c from Microsoft will likely make the FX cards the winner once true dual channel shaders are implemented and dual channel benefits can be accessed. The next incarnation of DX9 should include the ability to use simultaneous wait states for PS 2.0 textures in DX9 applications. This will greatly reduce the 'problem' shown in these 'benchmarks.' The DX9 SDK was built (without any hardware available mind you) to favor one long pipe (and thus currently favor the ATI 8x1 version) since each texture has to go through a myriad of call back and wait/check states and has a definite FIFO for all textures in the pipe the nV (4x2) pipe is crippled during these operations. With the next version of DX9 you'll see the included paired texture waits in the shader process allowing the nV to actually utilize the 4x2 pipe simultaneously instead of a defined FIFO for each.
