Re: A2 SCSI Partition Utility

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

"Joel" <joelbuckley54.nospam.@hotmail.com> wrote:

> I was thinking of a somewhat less ambitious approach to handling a 2GB drive
> on my IIgs.
> 
> Make 60 or so 32 Mb partitions.
> 
> System 6.01 can handle over 32 partitions, (though after about 30, the
> finder puts them all on top of each other on the desktop and you have to
> manually separate them.)

It is limited to 63 hard drive partitions in total over all drives on
all SCSI cards, because the driver data structures have a 6 bit limit on
the volume number for the driver.  (You could also have 63 CD-ROM
partitions, because that is a separate driver.)

> My idea is PU - a SCSI Partition Utility.
> This would let you rewrite the partition table to rearrange the order of the
> partitions.
> ProDOS 8 only allows you to see at most 14 partitions (fewer if you're using
> any other disk devices).
> PU would allow you to pick which ones and also to change which one is the
> boot partition.
> With that feature, I might also want to allow DOS3.3, CP/M and Pascal boot
> partitions as well.
> 
> This approach is probably a lot easier to implement and presents few
> compatibility problems.
> 
> Anybody have any thoughts on this idea?

Sounds reasonable, assuming that nothing will complain about partitions
being in a different physical order from their listings in the partition
table.  You would have to reboot in order to get the SCSI card and
drivers to update their tables (it might be possible to do this without
forcing a reboot, but it could be tricky).

In the case of ProDOS-8 2.x with an Apple High-Speed SCSI card, an even
simpler technique should be possible to allow use of more than 14
partitions.  The ProDOS kernel sets up an internal table which maps from
ProDOS unit numbers to SmartPort unit numbers.  All you need to do is
patch the table to access other partitions.  (The High-Speed SCSI card
is limited to 110 partitions, so no problem there.)

The original Apple SCSI card only supports 7 partitions (much less RAM
available on the card to hold the partition table) so this trick
wouldn't work.

It also wouldn't let you change the boot partition.
-- 
David Empson
dempson@actrix.gen.nz