First disk image of PLATO courseware for Apple II now available

["N.N. Thayer" <nnthayer@hotmail.com>]

Thanks to Antoine, we now have the first disk image of PLATO
courseware for the Apple II!  It's sitting in the Asimov /incoming
folder at the moment (I imagine it'll be moved to /images/
educational), but I've also sent it to the csa2 Gmail account.

This one is "Computer Literacy: Introduction", and it's an interesting
window into how the role of computers was perceived in 1982.  Given
the tremendous significance of the PLATO name - and, for that matter,
of Control Data Corp. - I considered preserving this disk to be more
important than usual, and didn't want it to rot away due to my lack of
skill.  Antoine graciously agreed to do the deprotection.  His details
are below:

*****

The disk uses a modified DOS 3.3 where:

- header markers were D5 AA 96 / FF FF instead of D5 AA 96 / DE AA
- data markers were D5 AA AD / FF FF instead of D5 AA AD / FF FF
- sync bits were changed from FF to AB
- nibble translation table was also changed: first entry value $96 was
changed to $AA

As it was probably not sufficient, there was a nibble sync at
$BB00 ;-)

1- Boot the disk, check the RWTS, understood the changes
2- Launched Advanced Demuffin 1.4, press B to get the original disk's
RWTS
3- Copied the disk
2b+3b- Launched Advanced Demuffin 1.4, press P to pass boot / Copied
T0/S0 to T0/SA (the original RWTS with no nibble translation table
change)
4- Updated the disk
5- Gotcha :-)

*****

Thanks again to Antoine for helping to preserve a little of the PLATO
legacy!