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MathGroup Archive 1994

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Re: PowerPCs

  • To: mathgroup at yoda.physics.unc.edu
  • Subject: Re: PowerPCs
  • From: Richard Mercer <richard at rmercer.wright.edu>
  • Date: Thu, 07 Jul 1994 11:34:35 -0700

Truth Is Stranger Than Fiction, Part III

>From a previous message of mine:

>     An example of what I am trying to avoid is on p.5 of the 5.30.94 MacWeek,  

> where a "Timing" result of ListPlot is given as 4.48 seconds on a PowerMac,  

> which does not include the considerable time for rendering the Postscript  

> graphic. This is claimed to take 27.3 seconds on a Quadra 700, a result which  

> almost certainly is total elapsed time. 


The actual command in question, printed in MacWeek, is
  Timing[ListPlot[Table[Prime[i],{i,10000}]],
    PlotJoined->True]]

I now have actual facts, and they are weird.

The Timing command actually does give results between 4.5 and 5.0 seconds on
a PowerMac 7100AV, so 4.48 is legit. The actual elapsed time is between 11 and  
12 seconds, due to the time required for Postscript rendering of 10,000 points  
and 9,999 line segments. (Why anyone felt it necessary to join these points is  
beyond me.)

On an actual Quadra 700, the Timing results were clustered around 24 seconds,  
however the actual elapsed time was around 29-30 seconds. The weird thing is  
that the Postscript rendering of the graph began consistently started after  
13-14 seconds. Thus it would seem the kernel calculations were completed in at  
least 10 seconds less than the Timing command would indicate.

Conclusions:

(1) The published timings are legitimate and represented no attempt to deceive.

(2) The ratio of the Timing results (roughly 6) is a wildly inaccurate 

    representation of the actual relative speed of the two machines. In total
    elapsed time the PowerMac was between 2.5 and 3 times faster than the 

    Quadra 700. It may have been 3-4 times faster in performing the kernel 

    calculations. (The PowerMac seemed to begin Postscript rendering after 3-4 

    seconds, slightly less than the Timing results.)

(3) The claim in that same MacWeek article that "Mathematica performs numerical 

    operations up to 10 times faster on a PowerMac than on any 680x0-based 

    machine and renders graphics up to 5 times faster" is at best highly 

    misleading, and probably cannot be substantiated by accurate timings.
    I stand by my earlier claim that Mathematica on the PowerMac is
    2-4 times faster than on Quadras (well, maybe 5 times faster than a Quadra 

    605!). 


Richard Mercer





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