Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!ucsd!sdcsvax!ucsdhub!cuuxun!cuuxb!fmcgee
From: fmcgee@cuuxb.ATT.COM (Netnews Administrator)
Newsgroups: comp.sys.att
Subject: Re: AT&T 6386 16 Mhz Speedup
Summary: no real performance boost
Keywords: 6386, Speedup
Message-ID: <2615@cuuxb.ATT.COM>
Date: 15 Mar 89 20:00:47 GMT
Expires: 29 Mar 89 00:00:00 GMT
References: <48@nisca.ircc.ohio-state.edu>
Reply-To: fmcgee@cuuxb.UUCP (Frank W. McGee)
Distribution: comp.sys.att
Organization: AT&T, Data Systems Group, Lisle, IL
Lines: 30

In article <48@nisca.ircc.ohio-state.edu> bobd@hpuxa.ircc.ohio-state.edu (Bob DeBula) writes:
>
>Last fall, I obtained an AT&T 6386 16 Mhz machine at a real reasonable (then)
>price.  While I was installing my ESDI drive, I took time out to examine
>the upside-down motherboard.  One peculiarity struck me immediately: the
>386 chip is marked 20Mhz!!! Apparently AT&T (Olivetti) must have decided 
>to standardize production.  I also located the 32.000 Mhz clock chip (I
>think).  Now the intriguing question is; Can I replace the clock chip (which
>appears to be soldered and I have no idea where to obtain the 40.000 Mhz
>equivalent) and get a 20 Mhz machine?  My orignial memory which came with the
>machine was 80ns (overkill I think).  I purchased 4 1Mb SIMMs from a chip

A few things.....The reason why the 20 Mhz. 386 is there is because
Olivetti couldn't get any more 16 Mhz. chips, so they substituted 20
Mhz. cpu's.  Since the board is designed to run at 16 Mhz., this
doesn't buy you any performance improvement.  I don't think you can
just change the crystal for a number of reasons.  The 20 Mhz.
motherboards are not that similar; they have some different PALs as
well.  In addition, the 20 Mhz. bus board is not compatible with the 16
Mhz. bus board, so I don't think your motherboard will be able to talk
to the busboard if you change the clock.  The 80 ns. memory is also a
similar situation to the 386 cpu's; they couldn't get 120's so the
substituted 80's.  Since the memory board is designed for 120's you
don't pick up any performance by substituting 80's.  Sorry, but doesn't
look like you can upgrade to 20 Mhz.

-- 
Frank McGee
Tier 3 Indirect Channel Sales Support
attmail!fmcgee