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From: minow@mountn.dec.com (Martin Minow)
Newsgroups: comp.sys.mac.hardware,comp.sys.mac.system
Subject: Re: Internal vs. External?  Which one wins?
Message-ID: <1918@mountn.dec.com>
Date: 18 Sep 90 14:58:18 GMT
References: <6947.26f4a5e4@umiami.miami.edu> <44888@apple.Apple.COM>
Reply-To: minow@mountn.UUCP (Martin Minow)
Followup-To: comp.sys.mac.hardware
Organization: Digital Equipment Corporation
Lines: 30

In article <6947.26f4a5e4@umiami.miami.edu> gross@umiami.miami.edu (JD144) 
attaches an external hard drive whose SCSI id is higher than the internal
drive, and wonder whether it will boot first.

Maybe.  In addition to the Set Startup considerations mentioned in
Scott Winders' (winders@aux.support.apple.com) reply, you should understand
that generic (not Mac-specific) SCSI disks that properly implement the
Ansi SCSI protocol will return a status condition to the Mac when they
are powered up.  The Mac should then ask the drive for the actual error
condition. The drive will then reply "I've just been reset" and the Mac
should ignore this.

Unfortunately, some Mac bootstraps treat this as a real error condition. Thus,
if you have a system on both an external (generic) and internal drives, you
might find the system booting only from the internal drive.  The simple
workaround is to boot from a diskette and move the System file on the
internal drive to an "Unused" folder.  Then, when you boot (on the Mac/SE),
the bootstrap will eventually find the system on the external drive.
It is rumored that this might not work on old Mac's as the bootstrap
resets the bus if it doesn't find a system (which causes the "I'm reset"
check condition to reoccur).  You'll know this if it happens on your system.

Many external drives have special firmware to work around the limitations
of the Apple bootstrap.  You'll probably see this problem only if you
use a "generic" SCSI drive.

Note that this is free advice; and worth what you paid for it.

Martin Minow
minow@bolt.enet.dec.com