gross@umiami.miami.edu (JD144) (09/17/90)
Hmm...maybe someone 'round here knows the answer...
If I have a Mac SE with an internal HD with a system, and I then attach
an external SCSI HD with a higher SCSI ID number than the internal and its
own system folder...shouldn't the drive with the higher SCSI ID boot before
the drive with the lower ID number? Or does the internal drive have some
sort of precedence over the external drive?
If you know..please tell me!
--
Jason Gross Comp Sci Ugrad University of Miami Class of '91 (?)
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The University of Miami has a lovely fountain. flaps@dgp.toronto.edu (Alan J Rosenthal) (09/18/90)
gross@umiami.miami.edu (JD144) writes: >If I have a Mac SE with an internal HD with a system, and I then attach >an external SCSI HD with a higher SCSI ID number than the internal and its >own system folder...shouldn't the drive with the higher SCSI ID boot before >the drive with the lower ID number? Not necessarily. See the "Startup Device" cdev in your friendly neighbourhood control panel. Click on the background of the control panel to select no drive; otherwise, the selected drive will boot first regardless of scsi numbers, unless it doesn't exist [or isn't bootable??] in which case the normal sequence is used. Note that the startup device cdev doesn't distinguish, in its display, between the two following states: - no scsi number is selected - no mounted volume has a scsi number equal to the selected scsi number. (Similarly, it is not possible to use the startup device cdev to set the startup scsi number to be a number not corresponding to a currently mounted volume (except for the special "no number" setting).) ajr
winders@aux.support.apple.com (Scott Winders) (09/18/90)
In article <6947.26f4a5e4@umiami.miami.edu> gross@umiami.miami.edu (JD144) writes: > If I have a Mac SE with an internal HD with a system, and I then attach > an external SCSI HD with a higher SCSI ID number than the internal and > its own system folder...shouldn't the drive with the higher SCSI ID boot > before the drive with the lower ID number? Or does the internal drive have > some sort of precedence over the external drive? Here is the correct order of devices checked during the startup sequence: 1. Floppy drive 0 (internal or right side of Macintosh II). 2. Floppy drive 1 (external or left side of Macintosh). 3. Floppy drive 2 (Macintosh SE with third floppy drive). 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. 6. NuBus startup devices. 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. Scott Winders internet: winders@aux.support.apple.com AppleLink: winders.s@applelink.apple.com
minow@mountn.dec.com (Martin Minow) (09/18/90)
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.comurlichs@smurf.sub.org (Matthias Urlichs) (09/18/90)
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)/Adam.Frix@p2.f200.n226.z1.FIDONET.ORG (Adam Frix) (09/20/90)
JD144 writes in a message on 17 Sep 90: JJ> If I have a Mac SE with an internal HD with a system, and I JJ> then attach an external SCSI HD with a higher SCSI ID number JJ> than the internal and its own system folder...shouldn't the JJ> drive with the higher SCSI ID boot before the drive with the JJ> lower ID number? Or does the internal drive have some sort JJ> of precedence over the external drive? ... With the emergence of the SE came the Startup Device cdev, through which you control what your startup volume is. What you describe is how the Plus handled things. On your SE, go to your Control Panel and (with all SCSI devices on) choose the Startup Device cdev. Highlight the volume you want to be the boot volume. This info gets stored in the PRAM of the SE and later. The Plus still acts as you describe. --Adam-- -- Adam Frix via cmhGate - Net 226 fido<=>uucp gateway Col, OH UUCP: ...!osu-cis!n8emr!cmhgate!200.2!Adam.Frix INET: Adam.Frix@p2.f200.n226.z1.FIDONET.ORG