Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!crdgw1!sixhub!davidsen
From: davidsen@sixhub.UUCP (Wm E. Davidsen Jr)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: Comparing 486 to 386 Systems
Message-ID: <3668@sixhub.UUCP>
Date: 11 Apr 91 02:19:06 GMT
References: <40409@netnews.upenn.edu> <1991Apr4.062503.1325@agate.berkeley.edu> <1991Apr4.142742.20601@lonex.radc.af.mil> <1991Apr4.204923.29300@agate.berkeley.edu> <27865@neptune.inf.ethz.ch>
Reply-To: davidsen@sixhub.UUCP (bill davidsen)
Organization: *IX Public Access UNIX, Schenectady NY
Lines: 39

In article <27865@neptune.inf.ethz.ch> brandis@inf.ethz.ch (Marc Brandis) writes:

| Well, I guess you subscribe to a similar notion which is also wrong, like most
| performance comparisons that oversimplify. In fact, (386-286) is the smallest
| of the differences, not by far the largest as your relation indicates. Give
| me any instruction on the 386 except multiplies that are faster than on the 
| 286. I know you will not find one. Of course, I am comparing apples to apples
| and oranges to oranges, namely CPUs running in the same mode at the same clock
| frequency.

  Fortunately we don't have to do that in the real world. We are
interested in how long it takes to get the computing done, and therefore
aren't limited to models which run on the 8086, nor at the same clock
frequency. In truth using the same mode and clock, only the 386->486
shows a major improvement.

  For real world problems, using arrays larger than 32k, integers larger
than 32k, and float values, the 386 in it's best (protected) mode is
about twice as fast as a 286, and the 486 is about twice as fast as the
386, *at the same clock speed*.

  This is not to knock direct comparisons, because if you're running a
64k application which only accesses bytes, and you are allergic to
frequencies faster than 4.77 MHz, or if you are comparing a 20MHz 286 vs
386, then the heads up comparison yields some useful info.

  For typical problems with source code, protected mode 386 or 486 run
much faster, even at the same clock, and the 486 uses fewer clock cycles
for most instructions, and with its burst mode supported in hardware it
runs faster yet due to fewer effective wait states.

  Comparing the fastest mode and model for each CPU isn't "fair" for a
frozen application, but the real world isn't fair, and applications get
updated to use the extra power.
-- 
bill davidsen - davidsen@sixhub.uucp (uunet!crdgw1!sixhub!davidsen)
    sysop *IX BBS and Public Access UNIX
    moderator of comp.binaries.ibm.pc and 80386 mailing list
"Stupidity, like virtue, is its own reward" -me