Size/Transistors

FiringSquad: How does Xbox 360 GPU compare in size to the RSX?

ATI: In terms of size, we’re a bit smaller. Of course, I’m not sure if that’s a good way to compare things, and to be honest I can’t talk about the number of transistors for this design. Microsoft owns the IP and that has a lot to do with their cost model and all that sort of stuff. But we’re a very efficient engine and we feel very good about our design. You know, the bang for the buck is awesome. The power of the platform [pauses] we’re going to be the most powerful platform out there, we’ve got a lot of innovation in there, we’re not just a PC chip.

I think the Sony chip is going to be more expensive and awkward. We make efficient use of our shaders, we have 64 threads that we can have on the processor at once. We have a thread buffer inside to keep the [inaudible]. The threads consist of 64 vertices or 64 pixels. We have a lot of work that we can do, a lot of sophistication that the developer never has to see.

FiringSquad: Looking at the parent die, what consumes the majority of the space?

ATI: The shaders consume a lot of the space. They don’t own 50% of the chip, but any one thing would be the shaders. 48 shaders, but again, they’re not 50% of the chip. We have texture units, we have shaders, we have caches, we have all kinds of things on the chip. We have a sequencer that controls the threads, we have lots of latency-reducing buffers. So the chip is complex.

FiringSquad: Which feature, or I guess group of features, really sets the Xbox 360 VPU apart from anything else?

ATI: Well, there can’t be one, I’ve got to go with two. The unified shader and the embedded DRAM are both unique and just really important to the success of the platform. They’re both powerful features that just allow you to do things you couldn’t otherwise do. They save bandwidth, they give you a richness. Did we talk with you about fluid reality yesterday?

FiringSquad: No, I don’t think so.

ATI: Well, what we’ve been trying to achieve in this particular go around is, well, realism, you can see it in games like Half-Life 2 where the walls, the environment, it all looks really good and you get a good sense of realism. But the next big hurdle is this fluid reality. The idea that characters in motion, lets say humans in motion, the joints look natural as they move along. That’s involves a lot of vertex processing, and with this unified shader we can put all these shaders towards vertex processing. Cloth, as it’s flying in the wind, like a flag for example, when it drops down on top of something, how that looks as it ripples.

Fur and feathers, the wind blows through them, grass, all that is where this idea of where fluid reality comes from. I’d say we’ve had static quality up until now, but now the fluid rhythm, the motion quality is this next realism that we’re really bringing.

Again, lots of power to devote to vertex processing, generating lots of pixels, to drive HD. HD is the platform of choice for this.