Why does the i7 processor report 8 cores?

[Gilles Gravier]

Hi, Sam!

On 01/02/2011 10:19, sam tygier wrote:
> On 01/02/11 04:35, Bill Stanley wrote:
>> I have an i7-860 processor in my computer. Linux (and Windows) report
>> it to have 8 cores available. I checked on the specs of the chip and
>> the specs say that it has 4 cores and 8 threads. It seems that the OS
>> is counting the treads as cores. It really doesn't matter much but
>> can somebody out there explain the discrepancy?
>>
>> Bill Stanley
>>
>
> run
> lscpu
> to see exactly what linux sees.
>

Bill, it's very simple. Your i7 is a quad-core processor, but each core
is capable of running 2 independent threads. Thus, the system reports
that it is capable of running 8 separate contexts... which is
interpreted by Linux (and Windows, and just about any OS) as 8 cores.

The difference is in fact not that big between 4 cores with 2 threads
per core, and 8 cores. But you do, every now and then, get into
ressource race conditions where it is percieveable. :)

On Sun's UltraSPARC processors, we have 8 cores and 8 threads per core
on the high end. Machines with 4 processors report 256 cores. :) When in
fact it's 256 threads and only 32 cores. But it's fun to see the 256
pinguins drawn at boot time when you run Linux on them...

Cheers,
Gilles