eeta@yoda.byu.edu (04/10/90)
On the question about getting quarter tracks:
To understand how this is done, you have to have a basic knowledge of
stepper motors. In a very BASIC sense, there are two phases; you rotate
the motor by energizing one phase, which starts the rotation, and then
energizing the second phase, which will cause movement to the quarter
track. Next, the first phase is deenergized, completing the "1/2" track
and the the last phase is de-energized, preparing for the next cycle.
To move the head in the opposite direction, you switch which phase is
energized first, and switch which phase is de-energized first. Now, for
the quarter-tracks... as I remember it, this is when the phases are
energized. So you end up reading/writing the tracks with the motor
energized, rather than de-energized as would be the normal case. This
is a major pain and is why anyone you ask will probably say it's not worth
the trouble to program. Also, if you were to attempt to put stuff on
every 3/4 track, imagine how messy the code could get to handle the seeks.
For a final wrench in the system, as I remember, when you turn off the drive,
you de-energize the stepper, so you can never STOP the drive on a 1/4 track,
only on a half track, further complicating things since ProDOS and DOS 3.3
both keep a record of which track the drive is on when turned off....
Well, that's enough rambling on the subject for now...
-Don Yacktman
eeta@yoda.byu.edu