Re: More than one CD-ROM drive with Apple IIgs and Apple SCSI card?

[dempson@actrix.gen.nz (David Empson)]

"Jason Whorton" <jason at microxl.com> wrote:

> Hello.  Can an Apple IIe (beige, enhanced) or IIgs (ROM 03) have more than
> one CD-ROM drive with an Apple regular SCSI card (I believe mine is REV C)
> or an Apple High Speed SCSI card?

Yes.  The Apple II SCSI card (either version) supports any mixture of at
most seven SCSI peripherals.  As long as the individual peripherals work
with the card and can be set to any SCSI ID, you can use them in any
combination you like.

You might run into the usual barrage of termination problems, of course.
With the original Apple SCSI card, you have to use two terminators if
you connect two or more devices to the SCSI card.  (The first and last
peripherals should be terminated.)  The High-Speed card has its own
termination, so only the last device in the chain should be terminated.
At least one device must be supplying termination power.

Some older SCSI peripherals are a bit flakey when used in combination
with others, and you might find that you have to rearrange the
connection order to get everything working.

There are other limits that you might hit:

Under ProDOS-8, the original Apple SCSI card only supports a maximum of
7 volumes/partitions over all drives connected to the SCSI card.  If you
had two CD-ROM drives and a hard drive with six partitions connected to
the card, you would not be able to access everything.

(The Apple High-Speed SCSI card's internal limit is 110 volumes, which
you aren't likely to run into.)

If you have an original Apple SCSI card with revision A or B firmware,
it doesn't support CD-ROM drives at all.

If you are running ProDOS-8 version 1.9 or earlier, you can only access
two volumes on an Apple SCSI card (unless the card is in slot 5, in
which case you can access four volumes provided slot 2 doesn't contain a
card which looks like a disk controller from ProDOS's point of view).

If you are running ProDOS-8 version 2.0 or later, you can theoretically
access as many as 13 volumes on an Apple High-Speed SCSI card (7 on the
original card).  The exact limit will depend on what cards you have
installed in other slots and how many drives are connected to them.

The limits for ProDOS-16 are similar to those for ProDOS-8 1.9 or
earlier.

GS/OS imposes a completely different set of limits: a maximum of 63
volumes in total for all devices of the same type (e.g. CD-ROM or hard
drive) connected to all cards in the machine.  You could theoretically
have six SCSI cards, each with seven CD-ROM drives, and be able to
access all of them (power supply and memory limits notwithstanding).  If
you tried to do the same thing with hard drives, and each drive had at
least two partitions, then some of the partitions would not be
accessable (2 * 6 * 7 = 84, which exceeds the limit of 63).

-- 
David Empson
dempson@actrix.gen.nz