Re: Daisychaining 5.25 " Drives

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

Knut Roll-Lund <kr-lund@nogarbage.online.no> wrote:

> Michael J. Mahon wrote:
> > Knut Roll-Lund wrote:
> >> Someone wrote earlier that a duodrive could be daisychained... I guess
> >> the 5.25" controller allows for this. Making it more than two drives
> >> but of course only one daisychain.
> > 
> > Nope--only two *drives*, regardless of how packaged.
> 
> It is what I thought, but is this true for all cards that work with the
> duodrive...

Correct.

> I would actually guess also that the dos (dos3.3 and prodos) 
> only copes with two drives per slot.

That is true for 5.25" drives using Apple's drives and controller (or
clones thereof) but it isn't the fault of ProDOS or DOS 3.3. It is a
limitation of the disk controller hardware and the signals available in
the cable. The operating systems are designed on the basis that there
can only be two drives in one slot.

It is not a valid assumption in general.

ProDOS-8 1.2 and later support four drives in slot 5, as long as you use
a suitable controller which has a ProDOS block driver in firmware which
obeys the established convention where ProDOS remaps the third and
fourth drives to appear like they are in slot 2. (This only works if
slot 2 doesn't contain a disk controller card or anything emulating
one.)

The main examples of this are the built-in SmartPort firmware on a IIc
and IIgs. For example, on a IIgs it is possible to use ProDOS-8 1.2 and
later and access two Apple 3.5 Drives plus two UniDisk 3.5 drives (or
some other combination also involving a RAM disk and/or ROM disk, and/or
four UniDisk 3.5 drives).

5.25" drives on the IIgs or IIc are handled separately - they appear in
slot 6, while 3.5" drives appear in slot 5, even though they are daisy
chained from the same connector. As far as DOS 3.3 or ProDOS is
concerned, the drives are on different slots.

ProDOS-8 2.x can potentially support up to 12 drives in one slot if you
have a controller which implements the SmartPort firmware interface, and
no other slots contain disk controller cards: the ProDOS kernel
allocates the unit numbers for unused slots to any SmartPort devices in
other slots which can't be addressed using normal methods.

GS/OS (on a IIgs) is even better - it can support a huge number of
logical volumes (drives or partitions) on a single slot. For example,
with an Apple SCSI card it could potentially support a total of 64 hard
drives and/or partitions over all SCSI cards (maximum of seven drives
per card).
-- 
David Empson
dempson@actrix.gen.nz