Trying to understand CPU reported

Oblivion

Nothing earth shattering ... just trying to understand what I'm seeing here.

Brand new Dell T3600 workstation with one Intel Xeon CPU E5-1620 at 3.6Ghz. This is a 4 core processor.

When I look in Device Manager - it correctly reports "Intel Xeon CPU E5-1620 0 @ 3.6Ghz" but it has this entry 8 times! I might have expected one entry for the CPU or even 4 entries because it is a 4 core processor, but why on earth is it showing 8 entries?



Running Win 7 Ultimate 32 bit.

Matt_Nixon

Your CPU will have 4 physical cores, each with 2 logical cores, thus the OS is reporting 8.

Oblivion

Matt_Nixon wrote: »

Your CPU will have 4 physical cores, each with 2 logical cores, thus the OS is reporting 8.

OK, thanks for that Matt. Interesting. I've just noticed that in Task Manager - Performance, there are also 8 CPU columns showing. The first four show the most activity on the graph whilst the last four show only slight ripples of activity. Presumably if I found something really CPU intensive to run those last four columns would show increased activity.

Anyway, the bottom line is that this machine is a godzillion times quicker that my 12 year old Dell with XP that this has now replaced, so I'm a happy if curious bunny.

securityguy

Oblivion wrote: »

OK, thanks for that Matt. Interesting. I've just noticed that in Task Manager - Performance, there are also 8 CPU columns showing. The first four show the most activity on the graph whilst the last four show only slight ripples of activity.

That's because hyperthreading relies on there being enough spare execution units within a core that you can run two, rather than one, threads on it (and on more exotic hardware, like Sun/Oracle "Niagra" chips, rather more than two). But if you've got n physical cores, it makes sense to put the first n threads on separate physical cores, because they are guaranteed to work properly. The fifth through eighth threads can then execute with a pretty good chance that the hyperthreading will give them what amounts to a physical core, but it's possible that it might not.