Cores versus Hyper-threading

[bob]

With multiple cores this does not happen, multiple cores is exactly the same as having multiple CPUs, they are just on one chip rather than on several.

Hi, thanks for the explanation; however, multiple CPUs do have hyper-threading.

I misunderstood, I thought having HT was the same as turning 4-cores into 8-cores.

Thank you,

Sean

A core is a CPU. A core with hyper-threading is a CPU with hyperthreading that behaves as I explained. You most likely do not want hyper-threading turned on when running a chess engine.

[bob]

As on P4, you can select to run 1 thread per physical core. Cores are always numbered in the same way; the program can select wich thread it will running on.

Is it possible for a process to turn off HT for itself then? AFAIK HT was only controllable on the P4 using the BIOS and there was no program control.
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Andy

Not so fast. The operating sees 2 cores on a single-cpu machine with hyper-threading enabled. If you buy a quad and turn on hyper-threading, it will see 8 cores total and won't know that every other one is a "phantom" hyper-threading core.