Re: Slot 'extender' dev cable

["David Wilson" <mcs6502@gmail.com>]

On Feb 4, 2:13 am, pau...@saaf.se (Paul Schlyter) wrote:
> In article <1170506846.660794.180...@v33g2000cwv.googlegroups.com>,
> David Wilson <mcs6...@gmail.com> wrote:

> > As I have a 40 track drive attached to a UDC card I simply updated the
> > ROM from 35 tracks (280 blocks) to 40 tracks (320 blocks) and I can
> > run completely standard ProDOS and applications with full 40 track
> > support.
>
> ....but what happens if you then insert a 35-track floppy?  I assume
> reading it would be OK, but if you tried to write it, could your patched
> ProDOS then attempt to write beyond the last (35'th) track?

The disk has a bitmap that shows where the free blocks are located.
The 35 track disk will only have free blocks in the range 0..279 so
writing new files will not attempt to use tracks that are not there.
Only direct use of the ProDOS BLOCK_WRITE call could attempt to use
tracks not formatted on a 35 track floppy disk.