CPU setting in BIOS

[ROYP123]

I am setting up an ASUS P8H61-M LE/CSM with the new kind of BIOS and am confused.
The CPU is an I3
In BIOS , the setting for active Processor Cores defaults to " all".
If that is selected, the task manager Performance bar shows 4 cores.
If I change the setting in BIOS to " 1 " the task manager performance bar shows 2 cores.

I know that the I3 is dual core.
Why does it show 4 cores when " all " selected, and what should I set in BIOS?
All or 1 ?
Thanks
Roy

[glc]

Leave it at "all". It's showing 4 cores because each core is hyperthreaded. If you set it to "1" you are shutting one core completely off.

[Eggo]

That's correct. I have an i3 too and though it's a dual core it shows 4 "logical" cores because of hyper-threading.

2 cores - 4 threads.

[ROYP123]

I will leave it at " all"

Thanks for your response.
Roy