[OT] multicore/cpu history

Peter J. Holzer hjp-python at hjp.at
Wed Apr 11 16:55:43 EDT 2018

On 2018-03-25 22:52:59 +0000, Steven D'Aprano wrote:
> On Sun, 25 Mar 2018 23:29:07 +0200, Peter J. Holzer wrote:
> >> >> By the way, multiple CPU machines are different from CPUs with
> >> >> multiple cores:
> >> >>
> >> >> http://smallbusiness.chron.com/multiple-cpu-vs-multicore-33195.html
> >> > 
> >> > Yeah, it was always "multiple CPUs", not "multiple cores" when I was
> >> > growing up.
> > 
> > Yes, but the difference is only an implementation detail.
> Not really. With multiple CPUs, you have the option of running two 
> distinct OSes in isolation, not merely virtual machines but actual 
> distinct machines in the same box.

Not in general, no. There may be hardware architectures which allow this
(if I remember correctly, hardware partitioning on HP and IBM unix
machines in the early noughties worked like this), but on a typical PC
motherboard this wouldn't work: There is a lot of shared hardware
outside of the CPUs, and two OSes running on different processors would
have to be aware of each other to avoid stepping on each other's toes.
And if they can do that, they can also do it on two cores of the same

In a normal SMP system, there is no real difference between having 2
8-core processors and 1 16-core processor from the OS's point of view.
The scheduler cares about it because caches and NUMA may make migrating
a process from one core to another more expensive depending on where
that other core is physically, but otherwise a core is processor.


   _  | Peter J. Holzer    | we build much bigger, better disasters now
|_|_) |                    | because we have much more sophisticated
| |   | hjp at hjp.at         | management tools.
__/   | http://www.hjp.at/ | -- Ross Anderson <https://www.edge.org/>
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