IGNcube: With the embedded RAM, was that a decision from the very beginning or was that added at a later date?
Greg Buchner: That was actually one of the "passionate" arguments, because making that step there's a huge benefit to system performance but there's also the addition of risk and cost. Nothing in life comes for free. It's one of those things [when decided] it changes what we want to do from a technology partnership with NEC, what kind of process we need, from tools, and it brings a new partner, MoSys, into the mix. It limits the choices of silicon providers because there's not many people who can do something like that. In fact very few people can do what NEC has done with this. They've done a phenomenal job.
So that was a decision where we said from a practical point of view, "Do we want to do this?" and just had a very rational discussion on pros and cons. In the end clearly we get a huge benefit. Not only from the embedded DRAM, but from how we structured it. One of the other products out there has embedded DRAM, but arguably they're not getting all the bang for the buck. They've got the cost in the silicon from a process point of view, but as for the performance in memory I don't think they have what we have -- or anything close to it.
IGNcube: Over half of the chip is embedded RAM, right?
Greg Buchner: On the version that shipped at launch it's on the order of a third. From a transistor point of view it's about half, but because it's a very regular structure it is very, very dense. So that half-transistor results in a much smaller area. So from an area point of view actually a little less than a third.
IGNcube: Is transform performance one of the big fights you had with using eDRAM, which takes up space?
Greg Buchner: That actually wasn't an issue. Those two are very separate discussions. You look at the embedded DRAM and it's going to be for performance on the fill rate side, and that's a cost trade-off. To get that kind of bandwidth with an external device, forget it, you're not going to even come close. So there's a huge benefit we get by having it.
Transform is a separate topic almost: how much do you shoot for, what's important, what are the typical cases with what developers are doing. Not many people send down triangles of the same color and never change anything else. It's these kind of fake benchmarks that are irrelevant. And so they're not streamed to data that is ever showing up in a game, so what's the point in measuring them? So what we went after is what's really happening in a game, what's really happening from a content creation point of view. We optimized around what the data patterns looked like and made a machine that screams for those kind of patterns.