Re: EDD Plus Card

[glen herrmannsfeldt <gah@ugcs.caltech.edu>]

Alex Freed wrote:

> Payton Byrd wrote:

> > I think the real problem is that the 1541 doesn't use the hole in the 
> > disk (the sensor isn't even there) to find sector 0, which is a 
> > requirement for Apple disks.

> I have no knowledge of the 1541, but Apple 5.25" drives never used the 
> index hole.

For soft sector disks the hole should only be needed at format time.

The controller starts writing data when the hole comes by, and stops 
when it comes by the next time.  Without an index hole the final gap
would need to be much larger to guarantee writing over all existing 
data, but not writing over the beginning of the track.   Another
possibility would be to write a simple pattern with no address marks
all the way around and then write the track.

If you can't be sure to write over everything there is the possibility
of an old sector header existing where it shouldn't be.

-- glen