Computer repair/assembly in Etobicoke?

[Lennart Sorensen]

On Thu, Jun 02, 2011 at 08:51:53AM -0400, Thomas Milne wrote:
> I can't believe the difference in speed between this Sempron and my old P4.
> Jeez, this is the lowest of the low of the AMD64...

That's the difference between a good CPU architecture and a really bad one.

IPC (instructions per clock) really matter, and the P4 was very bad.
Also long pipelines are not a good idea if your code isn't predictable,
and often it isn't.  Some P4s had pipelines with over 30 stages.  Get a
branch prediction wrong, and you are reverting back the work in most of
those 30 stages (a few at the start may be OK).  The amd64 chips tend
to be in the 10 to 15 range for the pipeline length.  They have less
than half as much wasted work to flush on a misprediction.  The Core 2
had 14 stage, and I believe the Core i3/5/7 do as well.

-- 
Len Sorensen
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