Re: 5.25 Question

[David.Empson@bbs.actrix.gen.nz]

In article <9211031336.AA11933@apple.com> FORDE@UV6.EGLIN.AF.MIL writes:
> Can anyone tell me if the standard 5.25 drives sold for the //GS (since the
> time ROM 3 was released) are 'Unidisks' or simply repackaged dumb 5.25
> drives? 

The IIgs 5.25" drive is EXACTLY the same as the IIe one.  It may have
a different coloured case, but the mechanism is identical.

> My daughter has an Apple //GS ROM 3 machine with two Apple 3.5 drives and
> one Apple 5.25 drive.  My son has an Apple //e with one 5.25 drive (bought
> in 1984) and one 3.5 Unidisk.  Presently, my son has the Unidisk
> controller in slot 7 and the 5.25 controller in slot 6.  He wants to swap
> those to allow booting from Apple Pascal 3.5 disks.

Apple Pascal 1.3 can be booted from a UniDisk 3.5 in slot 5.  If you
don't have a disk in the 5.25" drive, you need to Control-Reset then
type PR#5.

> The //GS Smartport will recognize the dumb drive's lack of communication
> and continue through its scan for a boot disk.  I believe the 5.25 Unidisks
> are themselves 'smart' and provide the same capability when mounted on a
> //e. 

Nope.  It is the IIgs 5.25" boot ROM ($C600-$C6FF) which provides the
'smarts'.  Rather than trying to read track 0, sector 0 in an infinite
loop, it has some kind of retry count or timeout, so it gives up if it
can't find a boot sector.  It then continues the boot process on the
next slot (5).

The IIe can't do this, because there isn't enough ROM space on the
5.25" controller card.  The IIgs's boot code jumps elsewhere to
perform part of this operation.

You could just leave a disk in the 5.25" drive which has a BASIC
program that does a PR#5 or PR#6 (depending on the slot arrangement
you settle on).

Note that if you put the 5.25" drive in slot 7, you won't be able to
access it AT ALL from Pascal.
-- 
David Empson

Internet: David.Empson@bbs.actrix.gen.nz    EMPSON_D@kosmos.wcc.govt.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand