Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!asuvax!hrc!gtephx!campbellb
From: campbellb@gtephx.UUCP (Brian Campbell)
Newsgroups: comp.sys.apple
Subject: Slot Assignments
Keywords: Slots, Booting
Message-ID: <447ed450.f759@gtephx.UUCP>
Date: 18 Jul 89 15:29:40 GMT
Distribution: na
Organization: AG Communication Systems, Phoenix, Arizona
Lines: 33

As Brian W. explained, 
it seems that software that requires a card to be in a certain hard-coded slot
position is a mark of sloppy programming.  I would agree that this generally
true, although there could be occasional exceptions.  Having flexible slot assignments
does make programming the card ROM more difficult.  It also seems that code must
be relocatable, and that means that JSRs in the ROM to subroutines in the ROM are
not possible.  Is this true?  Anyway, my main point is that even with flexible
slot assignments there is a "preferred" assignment scheme.  This means that the certain
cards are recommended in certain slots, but can be put in other locations at the users
discretion.  I thought this was due to the following reasoning.  Is this description
accurate and anywhere close to the mark?

In the pre-IIGS days, the apple bootup sequence always started
by scanning the slots, starting in slot 7, and continuing down to slot 1, if need be.
As soon as it finds a slot with a card, it stops scanning and it starts executing the
ROM on that card.  For example, since it never makes sense to boot off of a printer,
you put that down in a low slot position, like #1.  Since, it makes sense to boot off
of a disk, you put that in a high slot position.  But use #6 (not #7) in case you want
to add hard disk later.  It makes more sense to boot off of a hard disk if you have it,
so you want to put that in the highest slot (#7).  The point of all of this, is that
by using preferred slots you reduce the chances of having to re-arrange the positions
of existing cards when adding a new one.  For example, if you had a printer card in
slot 1, and a disk card in slot 2, where would you add the serial card that you bought
six months later?  If you put it in a higher slot the system would try to boot off of
it. You would have to keep moving your disk card to a higher slot position as you added
cards, unless it was in a high slot already.

With the IIGS, this behavior can be made obsolete.  From the control panel, one
can either specify that the old style scanning be done, or SPECIFY A PARTICULAR SLOT
to boot from.  This means that the cards can be in any ol' position, although, this
may not mean as much with the slots being predefined.  Or it may mean a lot.
I prefer to boot directly from slot 5 (via my 3.5" drive) rather than scan down to
slot 6 which has my 5.25" drive (which is often has either no disk or has a data disk).