Xref: utzoo comp.sys.mac.hardware:5380 comp.sys.mac.system:1507
Path: utzoo!attcan!uunet!snorkelwacker!ira.uka.de!smurf!urlichs
From: urlichs@smurf.sub.org (Matthias Urlichs)
Newsgroups: comp.sys.mac.hardware,comp.sys.mac.system
Subject: Re: Internal vs. External?  Which one wins?
Message-ID: <#-7jf2.fy1@smurf.sub.org>
Date: 18 Sep 90 16:47:41 GMT
References: <6947.26f4a5e4@umiami.miami.edu> <44888@apple.Apple.COM>
Organization: University of Karlsruhe, FRG
Lines: 33

In comp.sys.mac.hardware, article <44888@apple.Apple.COM>,
  winders@aux.support.apple.com (Scott Winders) writes:
< 
< Here is the correct order of devices checked during the startup sequence:
< 
< [...]
< 4. Startup device selected via the Startup Device cdev (this may include 
<    SCSI or NuBus startup devices).
< 5. SCSI devices beginning with ID 6 and ending with ID 0.

Two more hints:
- Some SCSI devices include the dreaded "Unit Attention" feature. (How to turn
  this off is vendor-specific, and not all SCSI installers can do it.)
  What this means is that, after a bus reset, the first command sent to the
  drive will get you an error message. In consequence, the Mac will only boot
  from such a drive if there's no other bootable device present on your
  system. (I.e., no other disk may have a System Folder on it.)
- Your Mac will wait for SCSI device 0 to become on-line before starting its
  boot sequence. Therefore, the disk which starts most slowly should have the
  ID 0, or else slower devices may not be recognized until you reboot for the
  first time.

< Both the Inside Macintosh V and the Macintosh Family Hardware Reference 
< manuals  state that the internal SCSI device is checked before any other 
< SCSI device, regardless of SCSI ID.  This is NOT True!  Unless the 
< internal SCSI device is selected as the startup device via the Startup 
< Device cdev it has no special priority during the startup process. 
< 
That section is probably worded somewhat ambiguous, and seems to mean the
same as my second remark above.
-- 
Matthias Urlichs -- urlichs@smurf.sub.org -- urlichs@smurf.ira.uka.de     /(o\
Humboldtstrasse 7 - 7500 Karlsruhe 1 - FRG -- +49+721+621127(0700-2330)   \o)/