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From: lyang%jennifer@Sun.COM (Larry Yang)
Newsgroups: comp.arch
Subject: Re: Am29000 and MIPS
Message-ID: <15274@sun.uucp>
Date: Wed, 18-Mar-87 18:37:40 EST
Article-I.D.: sun.15274
Posted: Wed Mar 18 18:37:40 1987
Date-Received: Fri, 20-Mar-87 04:19:06 EST
References: <15192@amdcad.UUCP> <1423@husc6.UUCP> <15213@amdcad.UUCP>
Sender: news@sun.uucp
Reply-To: lyang@sun.UUCP (Larry Yang)
Organization: Sun Microsystems, Mountain View
Lines: 37
Keywords: RISC MIPS

In article <15213@amdcad.UUCP> tim@amdcad.UUCP (Tim Olson) writes:
>In article <1423@husc6.UUCP> reiter@harvard.UUCP (Ehud Reiter) writes:
>>In article <15192@amdcad.UUCP> bcase@amdcad.UUCP (Brian Case) writes:
>>>The Am29000 ...  25 MHz clock (40 ns cycle time) ...
>>>25 MIPS max., 17 MIPS sustained running big programs
>>
>>MIPS is of course one of the most unfortunate terms in computer performance.
>>It seems to have two meanings:
>>   a)  how much faster a manufacturer thinks his machine is compared
>>to a VAX-11/780 (usually comparing integer C programs against a 4.2 BSD VAX
>>using standard Berkeley cc).
>>   b)  the number of million instructions per second that a computer executes.
>
>"MIPS" is not necessarily a meaninless indicator.  It can provide
>information on processor throughput (i.e. how much the processor is
>affected by pipeline stalls, jumps, cache and TLB misses...) when
>running real programs.  However, it must be combined with the number of
>instructions executed to derive the real measure of performance (1/s).

If the field of computer architecture existed in a vacuum, then (b)
would be the most important figure.  You can look at it to study how
the architecture performs despite branches, cache misses, etc.

But processors exist in the context of real world, where we all want
to be able to compare processors against the other.  That is why (a) is
a much more meaningful figure.

All in all, to use a *very* old joke:

	"MIPS = Meaningless Index of Processor Speed"

================================================================================

--Larry Yang [lyang@sun.com,{backbone}!sun!lyang]|   A REAL _|> /\ |
  Sun Microsystems, Inc., Mountain View, CA      | signature |   | | /-\ |-\ /-\
  "The attention span of a computer is only as   |          <|_/ \_| \_/\| |_\_|
   long as its electrical cord."                 |                _/          _/