Path: utzoo!utgpu!utstat!jarvis.csri.toronto.edu!mailrus!ames!pasteur!cogsci.berkeley.edu!jsilva
From: jsilva@cogsci.berkeley.edu (John Silva)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Computer Products United 386 16MHz
Keywords: Chapter Two.
Message-ID: <10866@pasteur.Berkeley.EDU>
Date: 9 Mar 89 19:28:16 GMT
References: <9804@ihlpb.ATT.COM>
Sender: news@pasteur.Berkeley.EDU
Reply-To: jsilva@cogsci.berkeley.edu.UUCP (John Silva)
Organization: University of California, Berkeley
Lines: 45

In article <9804@ihlpb.ATT.COM> bash@ihlpb.ATT.COM writes:
>Not too long ago I posted on how Computer Products United salesmen
>treated me in a fair and friendly manner in my quest for a 16MHz
>386 box.
>
[stuff deleted]
>
>The thing that bothers me about this is:  the processor is a 386 16MHz
>chip.  The motherboard is copyrighted as a 20MHz board.  There is 
>an oscillator speed jumper that sets the maximum clock speed at
>either 16 or 20 MHz.  This jumper is missing.  Possibly the clock
>will default to a 16MHz rate, but I doubt it.  I don't have a scope
>at home to actually measure the clock.  If they have the clock running 
>too fast the poor 386 would try to keep up as long as possible and 
>then give up (I've seen this trick in the world of Z80s.).  Anyway, to
>me, missing this jumper seems to be a blarring error.  I'm getting
>worried that this may be an indication of poor practices by their
>staff.  
>
>Then again. maybe it was a simple mistake.
>
>To be continued...
>
>Tom Basham

I've found that a considerable number of companies who advertise '20Mhz'
386 systems are shipping them with 16Mhz processors.  The reason for this
is that they will have a reasonably low failure rate within warranty, while
keeping costs down by using a cheaper processor.

A 16Mhz 386 can be successfully used at 20Mhz, *as long as they are kept cool*.
The reason for this is the chip will generate a certain amount of heat in
normal operation (which the specs account for), and running them at a higher
clock rate will generate excessive amounts of heat.  This reduces the life
of the processor, and the operating temperature range.

Generally, if you buy a 20Mhz 386 board with a 20Mhz processor you'll be paying
a little more for increased lifetime and reliability.  Running a 386 out of
spec isn't worth the hassle over the long run.

-J.
---
John P. Silva
INTERNET : jsilva@cogsci.berkeley.edu           "You don't know what you're
UUCP     : {backbone}!ucbvax!cogsci!jsilva       getting into, friend..."