You have it the opposite way round. x86 needs modern DDR-RAM for speed because of (bad!) legacy CPU design, while PPC is the opposite and is not sped up much by fast external RAM but is sped up greatly by extra cache. This is also why PPC is so good at cache-based calculation like RC5.
All CPUs need a fast interface to the rest of the system. Bad legacy CPU design? Uh, no. x86 CPUs run at a relatively high speed compared to main system RAM and you want to keep the CPU fed with instructions. Fast caches help with this problem.
Do you know why the G4 is sped up more by extra integrated cache as opposed to faster main system RAM? It's simple--Motorola has crippled the main system bus to 166 MHz SDR. So while the Athlon is at, what, 166 MHz DDR (333 MHz effective) and the P4 is a, what, 133 MHz QDR (533 MHz effective), the lowly G4 is forced to use 166 MHz or 133 MHz.
Already the vaunted Altivec units are hampered by being starved for instructions. This has been a complaint by coders on the Mac platform for a while. It's funny, the Mac has DDR DRAM but it only gets accessed through an SDR bus... the CPU is crippled.
That's the only reason that programs that can basically fit in cache (data and instructions for the critical loops) perform so well with the PPC... and heck, that's an ideal case for any CPU.
and it completely buries the Athlon per MHz. The 604e has a better FPU than both chips as well.
So? I don't see any 1.2 GHz 604e CPUs laying around, who cares? The CPU couldn't scale much higher and the manufacturers moved on. The relative efficiency of a 280 MHz CPU compared to modern CPUs of different architectures, even, has little to no practical relevence. I mean, a 68040 might have even better per-MHz FPU performance than even the new PPC970 but who would use that over the new CPU?
Anyway, the whole "x86 needs more bandwidth because it's poorly-designed" is a false assertion. ALL modern CPUs benefit from higher bandwidth to the main system memory. With the G4 there is no option for increasing that speed which is why y'all should be happy that there's a huge L3 cache included.
I like PPC but there are some shortcomings that can't be ignored for the current CPUs. That should all go away with the PPC970, a CPU I'm excited about.
