Re: 13-sector Disk ][ boot code AND CiderPress on DOS 3.1

[pausch@saaf.se (Paul Schlyter)]

In article <470ff848$0$14132$742ec2ed@news.sonic.net>,
Andy McFadden  <fadden@fadden.com> wrote:
> Chris Mosher <chris@mosher.mine.nu> wrote:
>> CiderPress will not recognize a freshly initialized 3.1 nibble disk image. 
>> The reason, I
>> discovered, is that the 3.1 INIT function doesn't write data fields for 
>> sectors that it
>> doesn't have any data for (it only writes address fields).
> 
> This is one of those situations where you either have to weaken the
> heuristic to support a rare case, or just not handle a rare case.  I
> usually managed to combine a weaker heuristic with some sort of backup
> test, or (for filesystem recognition) use weaker heuristics when manual
> intervention is involved.
> 
> The test as written was expecting to work around damaged tracks and sectors
> on formatted disks, and identify which of several encoding schemes was
> used (e.g. Muse sector-number-doubling), and wasn't expecting to find
> partially-formatted DOS 3.1 sectors.  I'll add "support for DOS 3.1 sectors"
> to the "to do" list.
> 
> The list is long and hasn't shrunk recently, so I'm glad you found a
> workaround.  The real fix might involve scoring address and data fields
> separately, with data fields on 13-sector disks being weighted less than
> address fields.  (The risk is incorrectly identifying a copy-protected
> disk with valid address fields but altered data fields.  We also need to
> see *some* data fields or we won't know if it's supposed to be 5+3 or 6+2.)

If you don't see any data fields at all, you can generally rule out
the 6+2 alternative, because a 6+2 disk almost always has data
fields.  And if you see no more than 13 address fields on that track,
you can definitely rule out the 6+2 alternative.....

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