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Interview: ATI and the Xbox 360

Interview: ATI and the Xbox 360 The Xbox 360 architecture
In the next of a new series of interviews with industry luminaries, we’re talking to ATI evangelist, Richard Huddy.

Richard is responsible for talking to Developers about ATI’s technology, and helping them to create technology that runs great on ATI hardware. Richard has previously lent his incredible graphics expertise to 3Dlabs and to NVIDIA. Most recently, he has been involved with the development and promotion of the graphics sub-system in the Xbox 360, designed for Microsoft by ATI.

The Xbox 360 architecture

I began by asking Richard for his opinion on the Xbox 360 archtecture. “I’m really impressed,” he commented, “It’s way better than I would have expected at this point in the history of 3D graphics. The unified shader architecture alone is capable of giving a performance increase of a factor of nearly two over the hardware that we have in PCs today. That’s because we see many cases, and this is particularly true on consoles, where games are limited by one of the two groups of engines in the graphics chip, either the vertex engines or the pixel engines. With a unified pipeline we can now devote 100% of the hardware to which ever task is the bottleneck.”

How does he think the sharing of memory between the graphics and the main memory will affect performance? Well, Richard explains that the shared memory is “Very different” from the technology implemented on the original Xbox, or even on today’s PC implementations.

“The intelligent memory gives pretty awesome speed – the bandwidth is up to 2 Terabits per second. That kind of power is almost unimaginable. The old terminology of ‘SMA (Shared Memory Architecture)’ simply doesn’t do justice to the flexibility and power of the Xbox 360. SMA is a term we have inherited from the PC and it usually has some negative connotations, but the Xbox 360 is really nothing like that.”

Interview: ATI and the Xbox 360 The Xbox 360 architecture

ATI’s Xenos Xbox chip

By now, you’d have to have been hidden under a rock to have avoided learning the details of the ATI graphics that power the 360, dubbed Xenos. 10MB of Embedded DRAM provide enough of a buffer to enable all 360 games to have Anti-Aliasing switched on, effectively for no performance hit. The question on everyone’s lips is: is this something that’s going to turn up on the PC any time soon?

“I’d be very surprised if these hardware features were implemented on the PC any time soon,” we’re told. “Microsoft has a very specific revision of DirectX (or Windows Graphics Foundation) for Xbox 360, just as they did with Xbox 1. DirectX for the PC includes no hardware specific instructions, because DirectX has to be 10 times more generic to work on a PC platform and the myriad of hardware configurations. I don’t think it will happen. Plus the architecture of the Xbox 360 is closed box – that means we can do special things there which have no comparison in the PC space.

"We practically have AA for free on the PC anyway right now. If the difference between 1280x1024 with no AA and 1280x1024 with 2x AA is 90 FPS and 70FPS, who wouldn’t turn the AA on? The performance hit isn’t going to be noticeable to most gamers – and with an X800 or X850 those kind of frame rates are common place.”