Path: utzoo!attcan!uunet!aplcen!uakari.primate.wisc.edu!zaphod.mps.ohio-state.edu!mips!prls!pyramid!ctnews!mitisft!burton
From: burton@mitisft.Convergent.COM (Philip Burton)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Can you speed up an old 6Mhz IBM-AT to 12Mhz?
Message-ID: <1526@mitisft.Convergent.COM>
Date: 7 Jul 90 00:33:07 GMT
References: <6692@vax1.acs.udel.EDU> <57993@bbn.BBN.COM> <3816@rodan.acs.syr.edu> <58011@bbn.BBN.COM>
Reply-To: burton@mitisft.UUCP (PUT YOUR NAME HERE)
Organization: Unisys Network Computing Group, San Jose
Lines: 37

In article <58011@bbn.BBN.COM> sher@labs-n.bbn.com (Lawrence D. Sher) writes:
>>In <3816@rodan.acs.syr.edu> amichiel@rodan.acs.syr.edu (Allen J Michielsen) writes:
>>>In article <57993@bbn.BBN.COM> sher@labs-n.bbn.com (Lawrence D. Sher) writes:
>>>>In article <6692@vax1.acs.udel.EDU> bach@vax1.udel.edu (Baskaran Subramaniam) 
>
>>>>>Is it possible to speed up an old 6Mhz IBM-AT (not a compatible) to 12Mhz
>>>>>by changing the crystal in it?
>
>>>clone 10 & 12 Mhz bus computers must not work.
>
>Amazingly, the timing specs for the ISA bus have never been published!  Look in
>bus at 8 MHz and the processor at some higher speed.  I believe that most
>(all?) 386-based ISA-bus machines do this.
>
>of the bus.  That, in turn, is constrained by the cards using the bus.  You may
>be lucky enough to have cards that can work at 10 MHz, but don't count on it.
>Once you opt for a solution that uses multiple clocks, more upgrade paths
>become possible, but none of them can reliably run the bus faster than 8 MHz.

I own an original IBM 6 MHz AT.  Years ago, people went wild when the discovered
that the original 6 MHz AT was "really" supposed to run at 8 Mhz.  A whole niche
industry sprung up to replace the original issue AT crystals with faster models.

I even spent money on two different solutions.  The one I kept was from a company
called Ariel, out of somewhere in NJ, I think.  

Using their product, I unplugged the standard crystal and replaced it with a
twist-dial unit that could run the system from 6 to about 12.5 Mhz.  My system
always locked up at about 9.6 - 9.8 Mhz, but I couldn't tell why. 

My neighbor has an 8 Mhz AT, and he was able to run his system up to about
11.5 Mhz reliably.  

This was an unscientific comparison because we didn't try the same complement
of adapter and memory cards, etc., in each system.

--Phil Burton--