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From: arends@metaphor.metaphor.com (Dale M Arends)
Newsgroups: comp.sys.mac.hardware
Subject: Re: How many terminators with 2 SCSI drives?
Summary: Two...
Keywords: SCSI terminators
Message-ID: <1178@metaphor.Metaphor.COM>
Date: 30 May 90 15:07:35 GMT
References: <1654@ac.dal.ca>
Sender: news@metaphor.Metaphor.COM
Reply-To: arends@metaphor.metaphor.com (Dale M Arends)
Followup-To: comp.sys.mac.hardware
Organization: Metaphor Computer Systems, Mountain View, CA
Lines: 44

In article <1654@ac.dal.ca> ireland@ac.dal.ca writes:
[ stuff deleted ]
>All the rest (six) said I had a termination problem, and that only the last
>drive in the daisy chain was supposed to be terminated.  Is this right?
>In my Jasmine Owner's Guide, it says that both ends of the chain are to be
>terminated, so one doesn't start removing terminators until the third SCSI
>device is added.  What's the scoop on terminators?  One at the end or one at
>each end?
>
>Thanks,  Keith Conover
>Keith@ac.dal.ca

It is really confusing the way documentation reads concerning terminators.
Simply put, only the first and last devices on the bus should have terminators.
The thing to remember is that the SCSI ID numbers are irrelevant in this.  
It is the first and last PHYSICAL CONNECTIONS that require terminators and
NO INTERMEDIATE DEVICES GET TERMINATORS.  So we have the following:

	1 internal drive or 1 external drive		Terminate it!
	1 internal drive and 1 external drive		Terminate both!
	no internal drive and 1 external drive		Terminate it!
	no internal drive and n external drives		Terminate FIRST
							and LAST external
	1 internal drive and n external drives		Terminate internal
							and LAST external

That's all there is to it (except finding out how to remove terminators if
necessary.)

The SCSI ID numbers are useful (from a user standpoint) to determine the 
startup device.  The internal drive should always be ID 0, the Mac is ID 7
and the IDs 1-6 are available to use for devices.  Oh yeah, the chain is 
scanned in reverse order so if the selected startup device has number 6, the
system may startup a little quicker.

Hope this clears things up.

Dale

-------------------------------------------------------------------------------
Dale M. Arends					Metaphor Computer Systems, Inc.
arends@metaphor.com
Any opinions expressed herein are my own and not those of my employer.  They
probably aren't interested and maybe don't agree and therefore ...