Originally posted by: MDme
pete... yes i am aware they are not directly comparable, i never implied that. but the xbox360gpu does not output 8 pixels per clock otherwise they'd be basically weaker than X800's since their fillrate would be 8 x the clock speed of the GPU ~ 500Mhz. If you see the article below, while they are not directly comparable, it has 48 pipelines which can process either vertex or pixel data. (and each pipeline can actually do 2 shader ops/sec)
http://www.techreport.com/etc/2005q2/xbox360-gpu/index.x?pg=1
Yes, Xenos is indeed capable of outputting (writing) only eight pixels per clock, AFAIK. 8p * 500MHz = 4Gp/s fillrate. (1280 * 720)p * 60Hz = .055Gp/s. Thus, Xenos will be more than physically capable of refreshing a 720p screen 60 times a second.
I read the TR article, and the more enlightening
FS interview, and the even more enlightening
IGN publication of MS' official rebuttal to PS3's specs, and the various B3D threads. Xenos does not have 48 pipelines. There's nothing in that TR article that suggests that:
On chip, the shaders are organized in three SIMD engines with 16 processors per unit, for a total of 48 shaders. Each of these shaders is comprised of four ALUs that can execute a single operation per cycle, so that each shader unit can execute four floating-point ops per cycle.
You really can't talk about Xenos in the same terms as a Voodoo (fillrate), or even a GeForce 6 (pipelines), because it's a rather unique architecture (unified shaders apparently not attached to/reserved for a pipeline, and ROPs literally on a separate die integrated with the EDRAM). "Fillrate" doesn't determine framerate in current games and the games we'll see on the new consoles. That said, an eight-pipe 6600GT has enough of it to hit
160fps in CoD (and probably higher in Q3), so obviously 8 pixels/clock at 500MHz won't hold be the limiting factor in Xenos (unless you expect console games to run at over 100fps). Shader power is the new performance benchmark, and that's where Xenos' 48 ALUs come into play.
So, no, no 48 pipes for Xenos, no 48 pixels drawn/written per clock. Not necessary, especially when aiming for efficiency in transistors and heat, and when pixels take more than a clock (or an ALU) to draw. 48 ALUs for shader work? Necessary.
Edit: Ah, maybe you thought I meant it could only work with or process eight pixels per clock. No, it can juggle quite a few more fragments at a time (Dave mentioned eight quads in flight, which seems like a surprising amount given current GPUs), it's just limited to
writing eight pixels per clock to the back buffer (from which it proceeds to the front buffer and then the display).