Subject: Re: More than 4 drives on a daisy-chain?--Maybe!
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From: david@uow.edu.au (David Wilson)
Newsgroups: comp.sys.apple2
Date: 17 Nov 99 10:14:56 GMT
Organization: University of Wollongong, Australia
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obsbedia2@aol.com (Obsbedia2) writes:
><< Finally there is a limit imposed by the operating system.  ProDOS-8 can
>only have 14 units in total, spread over all slots, including /RAM
>(leaving you with a limit of 13 real volumes).  >>

>Thank you for the run down.

>Is the above actually the OS or a firmware limitation?  I've see the prototype
>for the 10 Slot Apple II+.  With one slot for the memory card, it suggests
>being able to use 18 (less one for RAM) actual slots, and thus Volumes.

OS limitation. Smartport cards can support up to 127 devices and with 7 slots
you could have 889 volumes available - but ProDOS could only use the first 14.

ProDOS-8 uses a 4 bit field to represent the drive - 3 bits for slot number
(0-7) and one for drive number (1-2). The P8 Global page has a table of 16
device driver addresses at bf10-bf2f and a table of volumes at bf32-bf3f.
When P8 could finally get all 14 supported volumes online, the copyright message
at bf40 had to have a 00 byte placed at the front as otherwise programs that
assumed the volume table was null terminated would break.

I have successfully used slot 0 drive 2 as a drive but most any program that
used slot,drive rather than volume name to access it could not use it.

If you use Appletalk it may be possible to have more than 14 volumes accessable
by name as it inserts itself ahead of ProDOS.
--
David Wilson  School of IT & CS, Uni of Wollongong, Australia