Re: Partitioning & formatting a SCSI

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

David Wilson <david@uow.edu.au> wrote:

> "Arkain" <rwking@no.usa.spam.net> writes:
> >Where can I go to get programming details, tech docs & the like for the
> >Apple II SCSI Card?
> 
> I bought the Apple SCSI Card Technical Reference Manual either from A2 Central
> or Byteworks. This should be the definitive reference. Just be careful you
> get the one for your card and not the one for the later High Speed SCSI Card.

Neither of these manuals are particularly useful by themselves.  You
would also need good documentation on the SmartPort firmware interface
to be able to do very much.  I'd recommend the IIgs Firwmare Reference,
or the second edition of the IIc Technical Reference.  The latter is
available from Byte Works, but I don't know about the former.

In addition, much of the SCSI card technical documentation assumes you
know all about the SCSI command set.  To understand this, you need a
copy of the SCSI-2 standard, which should be available from ANSI or ISO
(but it isn't cheap).  A draft copy may still be available for free
somewhere on the Internet - this was enough for my purposes.

> >How many partitions will PRODOS let me see at once?
> 
> P8 v2.0.3 will allow 14 volumes online at once. 1 is reserved for /RAM on
> 128KB machines so P8's limit is 13 (assuming no other disk controllers are
> plugged into your A2).

ProDOS-8 has a variable limit which depends on the version.

ProDOS 1.0 through 1.1.1 only support two logical devices (partitions)
per slot.

ProDOS-8 1.2 through 1.9 will support up to four logical devices on
certain cards in slot 5 (notably the IIc and IIgs built-in disk
firmware, the SuperDrive card and the Apple SCSI cards).  To do this,
you must not have something which looks like a disk controller card in
slot 2.  The third and fourth logical drive appear to be slot 2 drives 1
and 2.

ProDOS-8 2.0 and later can use the SmartPort firmware interface on the
SCSI cards, and will remap extra partitions to slots which are not used
by cards which look like a disk controller (floppy disk controllers,
SCSI cards, RAM cards in standard slots, etc.).  If any of the used
slots only provide a single device (e.g. a RAM card) then the second
unit for that slot is not reused.

This means that the theoretical limit is 12 partitions, since it won't
remap a partition into S3,D1.  If you also had a floppy disk controller
in the system, the limit would be 10 partitions.  If you also had a
standard slot RAM card, the limit would be 8 partitions.


The RamFast uses a different mechanism, and can remap anywhere you like.
It has a menu-driven user interface which lets you choose the visible
partitions and map them to arbitrary unit numbers.  With the Apple
cards, you get a fixed mapping determined by the operating system.

> The Apple SCSI card has a limit as well but I cannot remember what it is
> (and I think it may be smaller than P8's limit).

The original Apple SCSI card has a limit of 7 partitions in total for
all drives connected to the card.

The Apple High-speed SCSI card has a limit of slightly over 100
partitions, but you can't actually use them all through ProDOS-8.  You
could write special code to access them through the SmartPort driver on
the card.

These limits only affect ProDOS-8.  Under GS/OS, there is a limit of 63
logical devices for each driver, i.e. 63 hard drive partitions plus 63
CD-ROM partitions, etc.  These limits must be shared between all Apple
SCSI cards in the system.

The RamFast has a separate driver, so you could theoretically have 63
partitions on all devices connected to one or more RamFast cards, plus
63 partitions on each type of device connected to all Apple SCSI cards.

If you actually tried to do this, you would probably go insane.

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P O Box 27-103, Wellington, New Zealand