Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!sjsca4!poffen
From: poffen@sj.ate.slb.com (Russell Poffenberger)
Newsgroups: comp.sys.ibm.pc.misc
Subject: Re: Difference between a 386 and a 386sx
Message-ID: <1990Sep20.190056.927@sj.ate.slb.com>
Date: 20 Sep 90 19:00:56 GMT
References: <935@sppy00.UUCP> <1477@sirius.ucs.adelaide.edu.au> <1990Sep19.225310.15663@Pacesetter.COM>
Reply-To: poffen@sj.ate.slb.com (Russell Poffenberger)
Organization: Schlumberger Technologies, San Jose, CA.
Lines: 58

In article <1990Sep19.225310.15663@Pacesetter.COM> torkil@Pacesetter.COM (Torkil Hammer) writes:
>In article <1477@sirius.ucs.adelaide.edu.au> msandifo@ucs.adelaide.edu.au (Martin Sandiford) writes:
># From article <935@sppy00.UUCP>, by jaa@sppy00.UUCP (Jeff Anderson):
># > In article <1990Sep16.194605.11968@ecn.purdue.edu> tlhilde@ecn.purdue.edu (Troy Hildebrand) writes:
># >>I have been warned _not_ to go with a 386sx when purchasing a computer,
># 
># This would seem to be a little unreasonable to me.  Maybe this person has
># an axe to grind?
>
>I remember reading in BYTE some months ago a warning against running
>unix and lookalikes (SCO Xenix) on 386SX's.  HOWEVER, the text warned not
>against the 386sx per se, but against cheap computers with unstable
>motherboards, second rate DRAMs not living up to the specs, and trying
>to run a 386SX at 20 MHz with just 1 MB of ram and 30 MB or so of disk..
>
>The warning against el cheapos makes sense, as a UNIX crash is a lot messier
>to recover from than a DOS crash, and as they recommend 4-8 MB of ram
>and something like 80 MB of disk.  There were a lot of cheapos made with
>386SX's, but not a lot with the more expensive DX.
>
>So there should be no problems with a respectable 386SX running at 16 MHz
>with enough 80 ns ram and enough disk for the application.  The SX is
>software compatible with the DX, and a SX system has a few advantages over
>the DX:
>
>The smaller bus and no cache leaves more room for goodies such as 8 MB on
>the motherboard and 8 expansion slots, and the simpler board is less likely
>to have design errors on it.  There is also the cheaper price for the same
>software capability.
>
>The SX is slower than the DX, which is the only tradeoff - or what?
>

You can get good dx motherboards with this kind of expandability. I have a
25Mhz 386DX (no cache), with 8Mb of ram on the motherboard (SIMM's) and has
8 expansion slots.

When buying an SX, the speed is affected by two factors..

1.) All 32 bit accesses take 2 memory cycles.
2.) The fastest SX Intel now makes is 20Mhz, whereas the slowest DX is 25Mhz.

(Yes, Intel used to make slower DX's, but according to my knowledge, not
anymore.)

The only real advantage I see of an SX over a DX, given well constructed
hardware, is the fact that RAM only need be upgraded in increments of 16 bits.

This means 512K at a time for 256K chips, or 2Mb at a time for 1M chips. In a
DX, you must use 32 bit increments, meaning 1Mb for 256K chips, or 4Mb for 1M
chips. If you have a DX that uses 1M chips, and you want only 2Mb more, you
must shell out more $$ and go with 4Mb.


Russ Poffenberger               DOMAIN: poffen@sj.ate.slb.com
Schlumberger Technologies       UUCP:   {uunet,decwrl,amdahl}!sjsca4!poffen
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