Re: Unidisk 3.5 won't write sometimes

["Peter Watson" <paw77@N_O_hotmail_S_P_A_M.com>]

"David Wilson" <david@uow.edu.au> wrote in message
news:41325d32$1@news.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?

I don't have any documentation, but I do have a few comments.

It's easy to forget in these days of multi-GB hard drives just what was
available at the time. ProDOS (and presumably SOS before it) were designed
at a time when a floppy disk held 140KB. Using up 2KB for the root directory
probably seemed plenty - you would have to work at getting 51 files onto a
5.25" floppy. And if you did fill it, there were always sub-directories.

Also, (in theory anyway) there was nothing stopping the root directory size
being increased. Well, nothing apart from developers making unjustified
assumptions about where the Volume Bit Map started!

Lastly, it's worth pointing out that MS-DOS also had a fixed, fairly small
root directory size.

On a different note, there's a good reason to avoid putting anything other
than subdirectories in the root directory of a ProDOS disk. If the root
directory is damaged, file recovery is *much* easier if the files are in a
sub-directory!
-- 
Peter Watson
-- Write to MSDOS disks on the Apple IIgs?
-- Impossible!  ;-)


"David Wilson" <david@uow.edu.au> wrote in message
news:41325d32$1@news.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