DOS feature on formatting disk

[gordonjcp at gjcp.net]

> Hi Gordon
>  There are a number of possibles but the track 0 sensor
> doesn't effect the incremental stepping mechanism used
> in these drives. There is no way that it can be off without
> being completely off and head over the wrong track.

If the head isn't sliding all the way back to the home position it can be
far enough back to close the track 0 sensor *but* still be about half a
track too far in.  This is how I have repaired about a dozen 720k drives
in old samplers.

Gordon.