[TUHS] PDP-11 legacy, C, and modern architectures

Tim Bradshaw tfb at tfeb.org
Fri Jun 29 01:39:58 AEST 2018

> On 28 Jun 2018, at 15:58, Larry McVoy <lm at mcvoy.com> wrote:
> You completely missed my point, I never said I was in favor of single
> cpu systems, I said I the speed of a single cpu to be fast no matter
> how many of them I get.  The opposite of wimpy.

And this also misses the point, I think.  Defining a core as 'wimpy' or not is dependent on when you make the definition: the Cray-1 was not wimpy when it was built, but it is now.  The interesting question is what happens to the performance of serial code on a core over time.  For a long time it has increased, famously, approximately exponentially.  There is good evidence that this is no longer the case and that per-core performance will fall off (or has fallen off in fact) that curve and may even become asymptotically constant.  If that's true, then in due course *all cores will become 'wimpy'*, and to exploit the performance available from systems we will *have* to deal with parallelism.

(Note I've said 'core' not 'CPU' for clarity even when it's anachronistic: I never know what the right terminology is now.)

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