Date   : Fri, 10 Nov 1989 22:33:12 GMT
From   : eru!luth!sunic!mcsun!unido!cosmo2!tilmann%cosmo.UUCP@bloom-beacon.mit.edu (Tilmann Reh)
Subject: on the other side of the floppy ...

Hello.

"snoopy" (Mathias Niemz) writes about problems with adapting his "multi-format 
bios" to the Alphatronic disk format.
But, the way of accessing the second side of the floppy is quite standard.
For remembrance: there are two ways of second-side access:
1. 'Sector Overflow'. The most usual method. The sectors of side 2 are
   processed after that of side 1 on the same track. So every track appears
   to have twice as much sectors for the BDOS.
2. 'Track Overflow'. Not that usual, but still standard and ok. The sectors
   of side 2 are processed after side 1 is finished, i.e. after maximum
   track on side 1 comes track 0 on side 2.
Every "multi-format bios" that wears this name for right, should be able
to process both ways of double-side access. So, I guess that Mathias doesn't
really have such a bios.
Just for the record: There is also a third way of accessing side 2.
One can mix the two methods mentioned above and will get the following:
The real order of sector processing is like 'sector overflow', but the
tracks are numbered equal on side 1 and odd on side 2. So, the BDOS thinks
of twice as much tracks (as with track overflow), but in fact there are
twice as much sectors. If you then choose an odd number of offset tracks,
the most real multi-format systems get in trouble (mine too), as they can't
divide the physical tracks into two logical tracks.

Tilmann Reh  (tilmann@cosmo.uucp)
.e