[Coco] Re: RETRIEVE utility...

[Torsten Dittel]

> I recall hearing that the Read Track command on the CoCo does not work
> reliably;  I wonder if that was your experience.  I heard this in
> connection with the Spit 'N Image utility for duplicating a copy-protected
> CoCo disk;  according to one of the authors, I heard second-hand, the
> program had to do several Read Tracks on the same track and kind of
> average them to get a reliable track image.

AFAIR the controller family had a "bug" (but I believe it was a feature)
with read track. If you'd write certain bit patterns within the sync
bytes (using the write track command), a read track returns some
reproducable trash after that bit patterns, but the bit patterns
themselves are different each time you read them. Different bit patterns
produce different trash, so a "read track - write track" doesn't work
(you just have to check the trash to know the track was copied that
way). It was used as a more sophisticated copy protection scheme.
However, read track will return almost everytime different sync bytes
but the sector data itself is always readable and separatable. Indeed if
you don't want to create a new "track structure" with all the correct
sync gaps before writing that track, it was a good idea to read it
several times until the sync info was good enough to write it back.

Torsten