XBOX 360 GPU power?

[Mordecaii]

I posted this elsewhere, but I figured this would be a more appropriate place to put it...


"Xenon", which has ATI produced the graphics at its core, have made suggestions like "The shader core has 48 Arithmetic Logic Units (ALUs) that can execute 64 simultaneous threads on groups of 64 vertices or pixels. ALUs are automatically and dynamically assigned to either pixel or vertex processing depending on load."


http://www.beyond3d.com/

Does this mean that the 360 will be able to do 64 shader ops per cycle? Also, is this directly comparable to the PS3 being able to do 136 shader ops per cycle? I'd really like it if someone a bit more informed than myself (aka cpiasminc) could answer this as I don't know whether the statement above translates into them saying the 360's GPU can do 64 shader ops per cycle or something else.

[cpiasminc]

This probably works out. In the CELL thread, I mentioned something similar that if you assume that 100% of the time, you'll be able to co-issue ops on the shader pipes, you can get a fourth ALUop for free on top of an otherwise existing 3 ALUops in one instruction. Presumably, based on the other figures they say, it looks as if ATI's ALUs can execute on both edges of the cycle, so instructions have half-cycle latencies instead of full-cycle(pretty much like the first XBox has). Anyway, this means 4/3 * 48 ALUs * 2 per cycle * 500 MHz comes out 64 billion shader ops per second. Of course, this is 64 billion in the same way that PS3 can do 100 billion. I think respectively, 48 billion and 75 billion are more realistic numbers for 360 and PS3.

At the same time, 136 shader ops per cycle for RSX does sound like an odd spec standing by itself without further knowledge of the GPU architecture. Ultimately, though, I think with half-cycle latencies, 360's GPU should realistically pull off 96 shader ops per cycle as opposed to RSX's 136.