Cheap PCs from Wal-Mart

Jim Lux 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
>         http://www6.tomshardware.com/cpu/20030521/index.html
>
>__

James Lux, P.E.
Spacecraft Telecommunications Section
Jet Propulsion Laboratory, Mail Stop 161-213
4800 Oak Grove Drive
Pasadena CA 91109
tel: (818)354-2075
fax: (818)393-6875

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