mikes@ncoast.UUCP (Mike Squires) (05/16/86)
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From peng!sir-alan!mikes Wed May 14 02:05:25 1986
To: peng!tlxprs!devon!paul
Subject: Hard drive addition
Cc: mikes peng!barry peng!ncoast!mikes
Date: Tue May 13 10:04:00 1986
Message-Id: <516434724.369@ncoast>
This won't be as organized as yours, but here goes.
First, this mod takes advantage of the fact that XENIX asks the number
of heads and cylinders at the time that a disk is formatted. It does
not ask the precomp time for the drive, nor the cylinder at which
precomp is changed. This means that most any drive can be formatted
but that some drives may have problems that accumulate over time
as the mismatch between the Tandy precomp and the precomp the drive
requires begins to cause read/write errors. This has not been a
problem with the CMI 6640 I use; this is the AT 33MB drive, I think.
I bought it because the CMI is a ripoff of the Tandon drive taht is
used by Tandy. I understand that the 35MB drive is the Quantum Q540
and that the 75MB is by Microscience. It would be a good idea to
find a drive that was similar in precomp to the Tandon 503 that
is used in the 15MB drive.
Secondly, my system has the Tandy kludge for a write protect switch
for the primary drive. It is also an external primary, which means
that the SCSI board in the drive case can daisy-chain four drives;
the internal drive can daisychain two. If you want to directly
replace the 15MB drive with another drive you have to figure out
how to add the Tandy kludge to your drive or how to disable it.
If, on the other hand, you simply make the old primary the secondary
drive and the new drive the primary drive, all you do is
1. Strap the old primary drive to be drive 1 (primary is drive 0).
This involves changing a jumper on the hard drive pc board. This
is the only jumper that requires a change.
2. Remove the termination resistor pack from the old primary drive, and
install it on the new primary drive. The control signals will run
from the SCSI card to the old primary and then to the new primary.
Mine works with no termination, but it seems best.....
3. Move the old primary data cable (20 conductor) from the SCSI
location 0 position to the 1 position.
4. If you have the external primary you will need a 34 conductor
cable that will plug into the back of the old primary case and
a 20 conductor cable that runs from the SCSI board (position 0)
to the new primary.
5. Turn it on, format, load XENIX, and your off.
This kludge has made my II/6000 upgrade as fast as the Tandy 35MB
system, and I still have the old 15 as a backup. I kept the full
system on the old primary for a while in case of trouble, but I have
had eight errors since December running 24 hours a day, all but one
on a single sector of a single track. I paid $350 for a surplus
CMI 6640 drive; I also bought a surplus case with PS and two DSDD
Shugart 860's that are now floppy drives 1 and 2. The 860's cannot
write boot tracks for reasons that I cannot fathom but work fine
on tar backups and mount diskettes.
The Syquest 5MB removable media hard drive is available surplus also;
this has a ST506 interface and should work fine as a mountable file
system.
I am getting (Real Soon Now) a Tandy 16 with the old 8MB 8" controller
in which the 8MB drive was replaced with a Quantum 2080. That's 80
MB of 20 ms access drive, a real screamer. The conversion is the same,
except that the cables are 50 pin for the control lines.
Quantum 2080's unused seem to sell for about $1500; Q540's for $700-900;
you could probably use one of the cheaper drives made for the AT which
are selling new for $500 - 1000.
Mike Squires
Allegheny College
Meadville, PA 16335
814-724-3360
{ncoast,peng,pitt}!sir-alan!mikes