[rescue] pursuing a VAX

[Joshua Snyder]

On Mon, 9 Dec 2002, Francisco Javier Mesa-Martinez wrote:

<snip>
>
> Pentium 4's are really weak when it comes to FPU, I assume that you CAD
> package is mostly FP-centric... However they have some nice INT numbers,
> which is what people use most of the day (UI, WordProcessing, etc).
>
> MHz per MHz the Pentium III is better than the 4, however the later was
> designed to scale better when it comes to speed, hence the ridiculous
> number of stages in its pipeline. The P4 also has some terrible penalties
> for things like missed branches (heck you have a lot of crap to flush on
> these deep pipelines).
>

Yeah, cycle for cycle the Pentium III is much faster than the P4.  The
best example that I have personally seen was a 850MHz Athlon that ran
circles around an original p4(1.5ghz).  The first P4's were the worst of
the bunch with only 256kB of L2 cache, you couldn't pay me to use one.
<rumor>I once heard that the original design for the p4 included a
secondary chip with a 512kB L2 cache, sort of like the Ppro.  The idea was
that the first P4's would be a high-end chip, and when the process
technologies caught up they would put it all on one chip, that would be
the low cost version of the chip.  When it was clear that the original p4
was going to cost to much, they had to put it all on one chip.  To do this
they had to reduce the size of the L2 cache 256kB, remove one of the
decoders and one the FPU pipelines.</rumor>

Not sure if any of it is true but seems to make sense when thinking about
adding SMT to the P4, you want to have wide issue cpu so the threads have
plenty of resources.  As it is now it seems like best reason to enable
SMT(no I am not going to call it hyper-threading... ) on the P4 is to make
up for the poor utilization caused by the long pipeline and slow filling of
the trace cache.  If the P4 had the extra resources we might see a better
performance when using SMT.

> Intel realized that their strength is not their microarchitecture, but
> rather their production technologies.. which so far almost nobody can
> beat. So that is what they are using, in the end it produces waht they
> wanted, some of the fastest CPU (at least in paper) on the market. Granted
> it is absolutely not an elegant way to do it. But like war, it is not
> about who has the prettiest uniforms, but rather about who gets to win it.
>

I totally agree, they looked at what good at and are taking advantage of
their strengths.

				josh

> Again, we come to another full circle in the computer industry. A decade
> ago there was the same debate: Speed Demons (MIPS, Alpha, HP-PA) vs.
> brainiacs (POWER, 88K).....
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