Path: utzoo!utgpu!water!watmath!clyde!mcdchg!ddsw1!bigtex!james
From: james@bigtex.uucp (James Van Artsdalen)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Intel 386SX chip & its applications
Message-ID: <3134@bigtex.uucp>
Date: 2 Jul 88 08:28:08 GMT
References: <206900116@prism> <6734@cup.portal.com> <6859@cup.portal.com> <11390@steinmetz.ge.com>
Reply-To: james@bigtex.UUCP (James Van Artsdalen)
Organization: F.B.N. Software, Austin TX
Lines: 28

IN article <11390@steinmetz.ge.com>, davidsen@crdos1.UUCP (bill davidsen) wrote:
> In article <6859@cup.portal.com> mslater@cup.portal.com writes:
  [ some 286 instructions are faster than 386 versions ]

>   I checked 25 instructions at random in the manuals without finding
> these instructions. I can't say that you're incorrect since I haven't
> check every one, but I really would like to know which instructions are
> slower...

You obviously didn't start at the front of the instruction set section.  :-)

The first four instructions (alphabetically) are faster on the 286.

However, the fifth (ADC) shows that the 386 *is* faster when dealing
with immediate operands.  I would hazard a guess this is really a
function of the 32-bit data width and not the ALU itself, and that the
386SX will not be faster than the 286 in this case.

All of these timings should be taken with a grain of salt: the manuals
tend to gloss over or ignore a lot of strangeness in processor
activity, particularly with regards to branches, and the only way to
really know these things is to get out a hardware probe.  Even then,
the 68030 is hard to measure: several instructions can be running at
once (as far as counting cycles goes), and many instructions appear to
execute in zero time due the the caches & parallel execution.
-- 
James R. Van Artsdalen   ...!ut-sally!utastro!bigtex!james   "Live Free or Die"
Home: 512-346-2444 Work: 328-0282; 110 Wild Basin Rd. Ste #230, Austin TX 78746