Originally posted by Programmer
I believe that the Cell's PPE does have a full FPU, including a double precision capability. IBM has said it is a full Power implementation, and that, by definition, includes double precision support. At 4+ GHz this Power core should perform roughly like a 970 of about half the clock rate (my estimate and is conservative).
I never doubted that. The G4 has full double-precision FP support, too. But the 970 has two full FP units. The question was not, can Cell do 64-bit FP, but can it muster the performance
of a 970 at 64-bit FP. (See below before answering.)
If you want to talk capability, they're all still catching up to the 68040's 80-bit FP capability.
Note that the SPEs have double precision capability added but it is not pipelined, so is "only" in the range of 25-30 GFLOPS for the entire chip. This compares well to a quad 970 arrangement. For most of the expected uses for Cell (and for most uses Apple would put it to), single precision is far more important -- OpenGL, Quartz2D, CoreImage, CoreAudio, etc. And on that score the Cell leaves all existing processors sitting on their asses wondering what the hell hit them.
I wasn't aware that the SPEs (or APUs, whatever—the little buggers hanging off the bus) had 64-bit FP at all. That does change things somewhat, although the need to have 1 thread per FPU makes it an elliptical answer at best to the 970's dual FPUs.
I'm not even going to try to contest that 32-bit FP performance will own everything. That would be true even if Cell only had its 4GHz AltiVec unit to fall back on.
I've got some reading to do this weekend.