Re: Unidisk 3.5 won't write sometimes

[David Wilson <david@uow.edu.au>]

>>Jeff Blakeney wrote:
>>>ProDOS disks, for some reason I've never quite figured out a
>>>satifactory answer for, have a fixed root directory size of 4 blocks.

Don't forget that the ProDOS disk format is actually SOS format. So most
limitations can be traced back to SOS (this still does not explain why
4 blocks [apart from the observation that having a directory occupying only
blocks 2..5 allows the bitmap to fit on track zero - so would 2..6]).

Does anyone have any SOS documentation that might provide an insight to this
design decision?

ProDOS officially supports two root directory sizes - 1 and 4 blocks. If you
read block 2 and the link to the next directory block is $0000 then the
disk has a 1 block root directory (with 12 entries).
If not, it has a 4 block root directory (with 12 + 3 x 13 = 51 entries).
-- 
David Wilson  School of IT & CS, Uni of Wollongong, Australia