Path: utzoo!attcan!uunet!optilink!cramer
From: cramer@optilink.UUCP (Clayton Cramer)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Can you speed up an old 6Mhz IBM-AT to 12Mhz?
Message-ID: <3971@optilink.UUCP>
Date: 6 Jul 90 17:47:40 GMT
References: <6692@vax1.acs.udel.EDU>
Organization: Optilink Corporation, Petaluma, CA
Lines: 36

In article <6692@vax1.acs.udel.EDU>, bach@vax1.acs.udel.EDU (Baskaran Subramaniam) writes:
> Is it possible to speed up an old 6Mhz IBM-AT (not a compatible) to 12Mhz
> by changing the crystal in it?
> 
> We have an 80287/6Mhz and 512K RAM+1128K AST Rampage card in it. I think, the 
> RAM chips have a speed of 120ns.  Would changing the crystal create any problem
> with using these?  Do I have to change the '287 and the RAM chips also?  Do I
> have to change the '286 chip itself?
> 
> I would appreciate any advice from the netters.
> 
> Baskaran.

When the AT first came out, it didn't take long to find out that the
margins designed into the motherboard by IBM were enough to allow use
of faster crystals, thereby speeding up the motherboard.  As a general
rule, the amount of speed-up you can get is variable from machine
to machine.  With three different ATs, we found different maximum
speeds.  One would run at 8Mhz, another at 10Mhz, and another at
a speed just under 9Mhz.  I didn't see any examples of IBM ATs
that tolerated 12Mhz.  Make sure that your RAM chips are fast enough
to tolerate the higher speed, but if it's a genuine IBM, they
PROBABLY will go faster.  Note that the change in crystals is
easy enough that if it doesn't work at 10, just change the crystal
again.

Make sure that the machine is COMPLETELY reliable before you 
commit yourself to that speed -- right at the hairy edge, some
such systems would work for a few minutes, until you loaded in
a large program, then failures would start to appear.

-- 
Clayton E. Cramer {pyramid,pixar,tekbspa}!optilink!cramer
Amtrak subsidies: adults playing with choo-choos.
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