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From: lange@ewa.cs.ucla.edu (Trent Lange)
Newsgroups: comp.sys.mac.misc
Subject: Re: The Fate of the Macintosh
Message-ID: <1991Mar24.080622.20610@cs.ucla.edu>
Date: 24 Mar 91 08:06:22 GMT
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In article <14020@medusa.cs.purdue.edu> krk@cs.purdue.EDU (Kevin Kuehl) writes:
>In article <1991Mar23.064856.4877@cs.ucla.edu> lange@lanai.cs.ucla.edu (Trent Lange) writes:
>
>   And, on straight number-crunching and/or programming tasks, the MIPS
>   ratings of machines, even across vendors and machines, does give a
>   decent ballpark estimate of relative performance.
>
>I agree for number-crunching, but not for programming tasks.  When you
>say programming tasks, I assume you are talking about such things as
>editing, compiling, debugging, etc.  In these cases brute CPU power is
>quite meaningless because the speed of your I/O devices such as the
>keyboard, disks and memory are the true limits to speed.  A good way
>to find this out is to use a timing program that counts the real time
>in a kernel, on the cpu and the total time taken.  From my estimates
>on Unix machines, a compiler spends about 2-3 seconds blocked for I/O
>for every 1 second it spends on the CPU.  And editing and debugging
>are going to be in the range 10-1000:1 for the most part.

Yes, many compiling and program running tasks are more I/O bound
than CPU bound.  But, in general, you can get the same amounts of
memory and the same I/O devices to run on low-MIP machines as on
high-MIP machines.  When this is done, then the difference in
performance is going to return generally to CPU performance
(also taking into account performance of the actual compilers
used, etc.), of which MIPS ratings give a semi-reliable ballpark
estimate.

>   But this is why MIPS ratings *are* somewhat useful when comparing
>   Macs and NeXTs, since the NeXTs *do* have a graphical interface that
>   is arguably at least as nice as the Mac's, and are comparable in many
>   other ways (even philosophically).  With those things the same, raw
>   performance definitely becomes an issue again for some people -- which
>   is where the MIPS come in.
>
>But what you forget is that the Mac and the NeXT have two completely
>different operating systems, buses and display systems.  The NeXT is
>going to seem somewhat slower than the MIPS figures would lead you to
>believe because of the overhead in displaying on such a large screen
>with PostScript.  Also it has MACH which will provide more of an
>overhead than the MacOS will because MACH provides a lot more services
>than the MacOS does.  They are somewhat useful, but only realizing
>that a NeXT is going to be faster than a IIfx.
>
>Kevin Kuehl
>krk@cs.purdue.edu
>kuehlkr@mentor.cc.purude.edu

Again, you're right, for most cases -- nobody should buy a NeXT because
they think it's going to pop its windows up faster than a Mac IIfx
will.  But they might want to because it's generally going to run
Mathematica or their long programs at least twice as quickly.

My point was that some people hold two things about their
computer to be of great importance -- its graphical interface and
its raw computing performance for number-crunching and programming
purposes.  I'm one of those people.  In my opinion, the NeXT is the
first computer to really challenge the Mac in the quality of its GUI.
Then the second issue becomes a factor -- and the NeXT's MIP rating
of twice that of a IIfx and other raw performance advantages
(i.e. DMA that it actually uses) becomes an important factor in
a purchasing decision.

The MIPS rating of a machine is indeed just one factor in evaluating
its usefulness and performance.  It is, however, definitely a
factor -- especially for certain tasks -- and not completely
irrelevant, as the poster I responded to originally claimed.

- Trent Lange

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