Wrong CPU Core count

[ChrisChros]

Hello,
I have a Intel Xeon E3-1275 v6 together with a ASRock Rack C236M WS. System is running fine but on the web page it shows me only 8 cores, but the CPU has 4 cores and 8 threads, so I would assume in total 12.
How can I check if the system really detects all cores and threads?

Thanks

 

[Heracles]

Hey Chris,

There is nothing wrong here : A CPU Core is an actual physical CPU that can do 1 thing at a time. Because CPU are often idle waiting about everything else, hyperthreading was developped for a single Core to look as capable of running 2 threads at once instead of one. 4 Core running 2 threads each gives you 8 threads.

But you can not have both :
Either you disable hyperthreading and can use your 4 cores
OR
You enable hyperthreading and can run up to 8 threads out of your CPU but now these 8 threads are the one using your Core.

See that as 4 physical CPU or 8 virtual ones. You will run either your physical CPUs or your virtual ones. But not both ways at once.

Hope this explains it a little better for you,

 

[ChrisChros]

@Heracles
thanks for your detailed explanation, now everything is clear to me.

 

[Arwen]

One reason that they say X cores & Y threads, is that other CPU Arch. have more threads per core;

SPARC T1 - 4 threads per core
SPARC M7 - 8 threads per core
POWER7 - 4 threads per core
POWER8 - 8 threads per core

At present, all main x86/x64 processors are either 1 thread per core. Or with hyperthreading available & enabled, 2 threads per core.

Note that there are current CPUs from both Intel and AMD that do not have hyperthreading available.