The best explanation of hyperthreading in reasonable terms has been this
one.
http://www.tomshardware.com/answers/id-1694436/hyperthreading-work.html
On Sep 6, 2016 7:48 PM, "Tom Jones" <
tomjones@centurylink.net> wrote:
> I have to answer these sorts of questions at work from time to time.
> Hyperthreading, for some reason, really throws people for a loop, no pun
> intended.
>
> Each "core" on a modern processor chip is, or would be if we could
> separate them, a CPU in it's own right. So if you have a four core CPU,
> that's actually four physical processors on a single chunk of silicon.
>
> Hyper-threading is done within a given core to make it appear as two
> cores. More or less it's a way to stuff the chip's execution pipelines so
> that two threads are interlaced and the CPU utilization is higher than when
> running a single thread. I'm sure someone on the list could come up with a
> better analogy, but that's all I got right now. Enabling hyperthreading is
> usually done at the BIOS level. To the OS it appears as two cores. So a
> four core processor with hyperthreading enabled will look like an eight
> core processor to the OS.
>
> At no time does the CPU divide itself from 64 to 32 bit subunits. If it
> is a 64 bit CPU with hyperthreading turned off, then it is a 64 bit CPU
> with hyperthreading turned on. Whether your programs are running as 64 or
> 32 bit will depend mostly on how they're compiled.
>
> ------------------------------
> *From: *"David Schwartz" <newsletters@thetoolwiz.com>
> *To: *"Main PLUG discussion list" <plug-discuss@lists.phxlinux.org>
> *Sent: *Tuesday, September 6, 2016 4:29:59 PM
> *Subject: *Re: 4 cores and 8 threads
>
> AFAIK, the “cores” are 64-bit ALUs that can split into 32-bit pairs to run
> 32-bit code.
>
> So an i7 has four x 64-bit cores that also work as 8×32-bit CPUs.
>
> Threads are an OS construct, unless you want to refer to them as “real”
> vs. “virtual”, in which case you’d have up to four 64-bit threads or eight
> 32-bit threads.
>
> I run VMWare, and I’ve never really bothered to figure out how it does its
> CPU mapping. I think I’ve given it two cores and 2GB of RAM and it does
> fine running Win 7.
>
> (My base system is a Mac with a 2.8 GHz i7, 16 GB of RAM, and the latest
> OS X.)
>
> -David Schwartz
>
> On Sep 6, 2016, at 3:53 PM, Keith Smith <techlists@phpcoderusa.com> wrote:
>
> Hi,
>
> If an Intel CPU has 4 cores and 8 threads will it look like 8 cores to
> VirtualBox when assigning resources to a guest?
>
> If so is there a way to determine which is a tread and which is actually a
> core?
>
> Thanks!! Keith ---------------------------------------------------
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