Path: utzoo!attcan!uunet!mailrus!cs.utexas.edu!helps!bigtex!james
From: james@bigtex.cactus.org (James Van Artsdalen)
Newsgroups: comp.sys.ibm.pc.misc
Subject: Re: Difference between a 386 and a 386sx
Keywords: 386 386sx
Message-ID: <47642@bigtex.cactus.org>
Date: 23 Sep 90 09:27:48 GMT
References: <1990Sep16.194605.11968@ecn.purdue.edu> <4383@bwdls58.UUCP> <14110@mentor.cc.purdue.edu> <4387@bwdls58.UUCP>
Reply-To: james@bigtex.cactus.org (James Van Artsdalen)
Organization: Institute of Applied Cosmology, Austin TX
Lines: 29

In <4387@bwdls58.UUCP>, mlord@bwdls58.bnr.ca (Mark Lord) wrote:

> In article <14110@mentor.cc.purdue.edu> edgincd2@mentor.cc.purdue.edu writes:

| If you wanted to determine whether or not the chip you are using is a
| 386 or a 386sx, couldn't you just execute some 32 bit intructions and
| time the number of machine cycles it takes to execute them.

> Good in theory.. but cannot be done.  In order to "time" them,
> you need to know the exact CPU clock rate, which is another unknown.

Why is it that you must know the CPU rate?

> Also, caches and stuff can affect this.

True enough.  But perhaps a cache would make the problem easier by
eliminating page misses and wait states...

> Ahha you say, so why not use 32-bit instructions that do not access
> memory?  Simple reason: that would not tell you anything, since the
> 386sx IS a 32-bit processor inside the chip.

OK, then let's use 32 bit instructions that *do* access memory.  On an
SX they'll take long because it takes two cycles.  So one could do a
"rep stosw" then a "rep stosd" and measure the ratio of time between
the two...
-- 
James R. Van Artsdalen          james@bigtex.cactus.org   "Live Free or Die"
Dell Computer Co    9505 Arboretum Blvd Austin TX 78759         512-338-8789