Cheap PCs from Wal-Mart
James.P.Lux at jpl.nasa.gov
Mon Jun 2 18:25:47 EDT 2003
Which P4 and Athlon were you comparing..
I went to the linked page at Toms Hardware and found reasonably close results
Athlon XP 3200+, and P4 3GHz...
Now, what's the power consumption of those two?
I think the P4 dissipates a max of 85W (poking around on the same Tom's page)
The C3 at 800 MHz dissipates 6.65W average and peaks at 12W
The Nehemiah at 1 GHz dissipates 11.25/15 W ave/pk
So, looking at the scaling and comparing P4 against Via C3 Nehemiah
Speed 6809/1591 4.3:1
Power 85/15 5.7:1
So the Via looks like it does more computes/Joule...
This is really a first order approximation. You'd have to look at
peripheral power, memory power, and power supply conversion and power
distribution efficiency. Peripherals and memory probably scale with memory
speed fairly linearly. The higher powered device will have more I^2R
losses in the power supply and distribution. (Supplying 50 or so Amps at
2-3V is no easy feat)
Here's the upshot... if you're in an environment where ultimate performance
is important, than you're probably best going with as few big fast
processors as you can get (the original Cray paradigm). On the other hand,
if you're in an environment where maximizing computation for a fixed amount
of power/heat dissipation resources (i.e. spaceflight or portable
operation), then things like the Via C3 start to look attractive, assuming
your task scales well.
Since I'm generally interested in resource(other than dollars) constrained
computing, I'd like to see more attention paid to computing per joule or
computing rate/watt. There are different tradeoffs whether you are
concerned about total energy (i.e. you're running off a battery) or whether
you have an instantaneous power dissipation limit (i.e. thermal radiators
in space). (that is, you can decide, do I want to run the calculation in
one hour at 200W, or over two hours at 100W)
At 02:42 PM 6/2/2003 -0400, Mark Hahn wrote:
> > re. the points on floating point performance, these are valid.
> > But I think we should note the new Nehemiah boards which are just out.
> > Well worth looking at I think - I intend to get one soon, and I'll report
> > back if/when I do.
> > http://www.mini-itx.com/reviews/nehemiah/?page=10#s21
>hmm. for rhetorical purposes, let's compare the numbers from this article
>to two high-end unis:
> dhry whet mmi mmf memi memf
>e800 1048 285 963 1588 194 208
>e10k 1300 351 1193 1968 233 245
>e10k-n 1591 366 2255 2285 664 389
>p4 6809 9327 22170 13896 5050 5041
>ath 3319 8855 13011 12217 2912 3080
>I think it's pretty clear that you need to expect much lower
>performance from even the 'high-end' VIA chips. if your code
>more resembles dhrystone (mostly integer, cache friendly),
>then you can mostly expect to scale with clock speed, and the
>VIA chips might be attractive on a speed/(heat*cost) basis.
>for general clusters, where memory bandwidth and FP performance
>and integrated gigabit are big advantages, VIA doesn't compete.
>data is from the article above and
James Lux, P.E.
Spacecraft Telecommunications Section
Jet Propulsion Laboratory, Mail Stop 161-213
4800 Oak Grove Drive
Pasadena CA 91109
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