Linked by Nicholas Blachford on Wed 9th Jul 2003 16:43 UTC
Talk, Rumors, X Versus Y This article started life when I was asked to write a comparison of x86 and PowerPC CPUs for work. We produce PowerPC based systems and are often asked why we use PowerPC CPUs instead of x86 so a comparison is rather useful. While I have had an interest in CPUs for quite some time but I have never explored this issue in any detail so writing the document proved an interesting exercise. I thought my conclusions would be of interest to OSNews readers so I've done more research and written this new, rather more detailed article. This article is concerned with the technical differences between the families not the market differences.
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Re: Roy
by Bascule on Wed 9th Jul 2003 18:52 UTC

The Power5 SMT vs. Pentium4 HT is particularly blatent (though I have no doubt that Power5 SMT will provide more improvement than Pentium4 SMT, I doubt it will double performance and even then it will only improve parallel stuff - much more important for servers than desktops).

HyperThreading is a hack designed to utilize execution units of the P4 which sit idle as a tainted trace cache is cleared and its pipeline is repopulated following a mispredicted branch. If you work the numbers on the Pentium 4, you'll find that the percentage of time its execution units sit idle is approximately equal to the percentage of branch instructions in the code it is executing.

SMT in the Power5, on the other hand, is designed to leverage the full power of a dual core processor by allowing the pipelines to pick and choose which execution units to send decoded instructions to, with the assumption that the entire pool of execution units on both cores won't be completely used at a given time when they are being fed by only two pipelines.