All this talk about hyperthreading raises a question in my mind. If I have a Pentium 4 3GHz with hyperthreading disabled, does that mean it basically runs at the speed of a 1.5GHz pentium?
No, it would run like a single Pentium 4 3GHz. With hyperthreading enabled, Linux actually sees two CPUs. So, it completely depends on how well your OS handles SMP. This is my experience at least. It may be that Intel does some SMP stuff for you at some level or another by stuffing both pipes. This page from intel seems to back my claim:
http://www.intel.com/support/platform/ht/os.htm
Here's another quote from Intel:
"The result is greater performance and system responsiveness when running multiple applications at once. So you can multitask like never before."
ref: http://www.intel.com/homepage/land/hyperthreading.htm
This says to me that the only time hyperthreading works to improve your machine is when you have an OS that can farm processes to two CPUs.
--Dave
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