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From: olson@anchor.esd.sgi.com (Dave Olson)
Newsgroups: comp.sys.sgi
Subject: Re: Hardware question on 4D/20
Message-ID: <9914@odin.corp.sgi.com>
Date: 3 Jul 90 17:27:33 GMT
References: <1990Jul3.063306.28718@ariel.unm.edu>
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Organization: Silicon Graphics, Inc.  Mountain View, CA
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jcmiller@hydra.unm.edu (Jeff Miller) writes:


| 	Hello fellow SGI users!!
| 
| 	I have a couple of hardware questions for all of you GURU's out there:
| 
| (1) What is involved in upgrading a 4D/20 to a 4D/25? I am willing to perform
| the surgery myself. I believe that it involves replacing the R3000 and R3010
| CPU and FPU with faster components and, of course, faster RAM. In addition, 
| there seems to be room to install 64Kb of cache RAM in place of the existing
| 8Kb cache. Is there any special hardware swith to tell the CPU that it has
| more cache? 
| ( Yes, I know the proceding proposal definitely voids my warranty-- if I
| still had one :-)

I won't speak to the rest, but some other things that you get with a
4D25 are a faster SCSI chip, and a new I/O controller chip.  The
combination boosts disk throughput considerably.  Since the I/O chip is
an SGI chip, you can't just buy one.  The SCSI chip is the WD 33C93A,
instead of the 33C93.  Just changing the SCSI chip won't help a whole
lot without the new I/O chip (I seem to recall about 10% improvement
with just the 93A).  The types of the I/O and SCSI chips are determined
independently of each other.

I also seem to recall that there was some minor board layout required
to accomodate the higher clock rate, and some PAL changes.

The cache is sized at boot time; I don't know if the 4D20 cpu board
really supports more cache than is present; I am not a hardware
person.

And, as you note, you have completely violated your warranty, and if
you blow it, you lose...
--

	Dave Olson

Life would be so much easier if we could just look at the source code.