Unified architecture gives Xbox 360 the graphical edge - ATI

Microsoft's Xbox 360 will have better graphics performance than the PlayStation 3 despite the better on-paper specifications of the Sony console, according to graphics chip designer ATI's Richard Huddy.

Speaking in an interview with techie website bit-tech.net, Huddy - ATI's developer liaison and technology evangelist - went into detail about the Xenos chipset used in Xbox 360, and how it stacks up against NVIDIA's RSX part for the PlayStation 3.

Although the RSX is more powerful in terms of raw specifications - it runs at a higher clock speed for a start, 550Mhz rather than the 500Mhz speed of the Xenos part - Huddy claims that the unified shader architecture used by ATI will give Xbox 360 the graphical edge.

"That mere 10 per cent clock speed that RSX has on Xenos is easily countered by the unified shader architecture that we've implemented," he claimed. "Rather than separate pixel and vertex pipelines, we've created a single unified pipeline that can do both."

"Providing developers throw instructions at our architecture in the right way, Xenos can run at 100 per cent efficiency all the time, rather than having some pipeline instructions waiting for others," Huddy explained. "For comparison, most high-end PC chips run at 50-60% typical efficiency. The super cool point is that 'in the right way' just means 'give us plenty of work to do'. The hardware manages itself."

For its part, NVIDIA has repeatedly downplayed the importance of unified shader architecture, and has publicly stated that it doesn't believe that this is the best path to improved graphics performance.

Huddy believes that this position is marketing bluster from NVIDIA, rather than being based on any genuinely held beliefs about the technology in question.

"This time around, they don't have the architecture and we do, so they have to knock it and say it isn't worthwhile," he said. "But in the future, they'll market themselves out of this corner, claiming that they've cracked how to do it best. But RSX isn't unified, and this is why I think PS3 will almost certainly be slower and less powerful."

Of course, neither the RSX nor the Xenos exists in final silicon form yet, and the claims of both NVIDIA and ATI need to be taken with a hefty pinch of salt as a result. Although they're both based on IBM-manufactured chips and PC-like graphics parts, the architecture of the Xbox 360 and the PS3 is radically different and direct comparisons are difficult.

However, many developers working with both consoles up to now have privately concluded that Sony's system, which will be launched at least six months after Microsoft's, will have the edge in terms of overall performance.