Milo, Re: "If it was a 2Ghz P/// I'd expect ~100% faster then a 1Ghz P///"
Why would you expect that? No CPU scales exactly linearly over broad megahertz ranges, least of all the Pentium III, which has a rather large memory bottleneck. I suppose if you gave a Pentium III the same front side bus and memory setup as the Pentium 4, it may scale a little better.
At 2.0GHz, a Pentium III with 133MHz front side bus would have a 15x multiplier. Even the Celeron at 766MHz had an 11.5x multiplier, and you know how efficiently that performed.
Here are some Quake III scores from Anandtech that show the Pentium III scaling.
anandtech.com
Pentium III 600MHz/133MHz - 106.2
Pentium III 800MHz/133MHz - 123.8
Pentium III 1.0GHz/133MHz - 136.9
800/600 = 33%, PIII 800/PIII 600 = 16.6%
1000/800 = 25%, PIII 1000/PIII 800 = 10.6%
anandtech.com
Pentium III 1.0GHz/133MHz - 143.4
Pentium III 1.2GHz/133MHz - 169.2
1200/1000 = 20%, PIII 1200/PIII 1000 = 18%
And that's with the benefit of Tualatin enhancements, and it still doesn't scale linearly.
From the same test,
Athlon 1.2GHz - 179.6
Athlon 1.4GHz - 190.2
1400/1200 = 16.6%, Athlon 1200/Athlon 1400 - 6%
Pentium 4 1.3GHz - 185.5
Pentium 4 1.5GHz - 201.5
Pentium 4 1.8GHz - 226.7
1500/1300 = 15.4%, P4 1500/P4 1300 = 8.6%
1800/1300 = 38.5%, P4 1800/P4 1300 = 22.2%
If a 33% increase in Pentium III performance yields a 16.6% performance improvement, even assuming that the graph continued linearly (which it wouldn't), a 2.0GHz Pentium III would only be 50% faster than a 1.0GHz Pentium III. Therefore, the Pentium 4 has better IPC than the Pentium III.
Considering the Athlon, a 16.6% frequency improvement only yielded a 6% performance improvement, which is one third the performance improvement per clock improvement. However, the Pentium 4 gets a 22.2% performance improvement with a 38.5% clock improvement, which is a much better ratio than the Athlon, or the Pentium III. Eventually, taking each chip out farther in megahertz, the Pentium 4 has the memory bandwidth to scale better, and IPC would eventually converge, with the Pentium 4 coming out victorious.
But then again, this is only Quake III. There are other benchmarks, and some that probably don't exhibit these favorable conditions. But it just goes to show that you are wrong about your IPC estimates.
wanna_bmw |
