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From: c184-au@holden.Berkeley.EDU (Dan Filner)
Newsgroups: comp.sys.atari.st
Subject: Hard Disks
Message-ID: <11000@pasteur.Berkeley.EDU>
Date: 12 Mar 89 22:16:34 GMT
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Reply-To: c184-au@holden.Berkeley.EDU (Dan Filner)
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Organization: University of California, Berkeley
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There was a good article in STart by Dave Small a few years back about 
how to attach two hard disk mechs to a currently functioning hard drive.
It works something like this :
One drive has to be logical unit 0, one drive has to be logical unit 1.
Set the jumpers/switches/whatever on the disk mechs in this manner.
Both drives are connected by a (non-twisted) 34 pin ribbon cable.  The
cable runs from one drive mech to the next drive mech to the seagate->scsi
interface. The drive that is in the middle has its terminating resistor
removed. The one on the end doesn't : it is the terminating drive.
Each drive is connected by a 20 pin cable to the interface. 
Logically selected drive 0 is connected to the interface's connection #0,
drive #1 goes to interface connection #1.  Both drives need power, and
that's just about everything you need to know.
Some 34 pin cables have a 5-pin segment twisted around between two of
the connectors.. this is for swapping drive select signals -- in this
case I believe that both disk mechs should be set to logical unit 0.
(I use a non-twisted cable..)
I followed the article by Small in STart when I hooked up my system
and have had few troubles.

  The system I use is a BMS ACSI-->SCSI interface, an adaptec 4070
SCSI-->ST506(RLL) interface, a Seagate 238R and a Seagate 277R.
This totals approximately 95 MB at a cost of around $1000.
The BMS board doesn't seem to have attracted much attention on this
Newsgroup discussion.. I recommend it, especially if you're in the
Berkeley area.  When my hard disk died (my own fault), I took my
system to their shack and they  kindly helped me out with data recovery.

No fancy sign off -
Dan Filner
c184-au@holden.berkeley.edu