>>This is, at least partly, a hardware design problem.  I know that you can
>>do this on the RS6000 and perhaps a few others, but usually the SCSI bus
>>hardware on most systems will react to this by wedging.

>Are you sure?  I've yanked my CD-ROM drive off my NetBSD machine after
>booting, to use on my Windows machine, many times without a problem.
>I sometimes then bring it back and plug it in, without rebooting, to
>read something off a CD.  No problems.  I've also done this with tape
>drives.

I've wedged my '42CF a few times by messing with the cable to my ZIP drive.

I would think that disconnecting a SCSI cable from a running system would
be a really Bad Thing all around anyway. If you happen to pull it at
an odd angle and your ground cables disconnect before the signal cables,
you stand a good chance of introducting spikes and other transients into
your system. Especially in the case of external devices like the ZIP drive,
where the power supply for the ZIP drive is an isolated one (the chassy of
the drive is allowed to 'float' at any voltage level if the grounding 
cables are not connected).

Not that this is quite as relevant, but a long time ago I fried several
serial port boards in my Radio Shack TRS-80 because the other computer it
was connected to was plugged into a different outlet across the room .. an
outlet which happened to be on the _opposite phase_ of the 240VAC coming
into the house. That an a slightly faulty grounding lug on one of the
three-prong wall outlets led to the possibility of a 240VAC difference
between the chasses of the two computers during that tiny little time
when the cable was being disconnected..

Since then I've always felt that disconnecting certain types of cables
while the system is on is a bad idea..

Cheers,
Phil
--
Phillip F Knaack               flipk@iastate.edu
Database Programmer, NCREMP    Student Development Group
ISU Extension                  Project Vincent, Iowa State University