Re: 3.5" UniDisk Bug

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

"Wayne Stewart" <waynes@intergate.ca> wrote in message
36cd6118.0106021257.69e5f0ce@posting.google.com">news:36cd6118.0106021257.69e5f0ce@posting.google.com...
> I was reading the December issue of Call-A.P.P.L.E. and it mentioned a bug
in
> the 3.5" UniDisk when used with the UniDisk controler. It said the bug
only
> came into play with some drives when trying to write to a write-protected
disk.
> Anyone have any details on this? It said that Apple was correcting this on
new
> drives but didn't elaborate.

Hmm, December in what year?  :-)

The Apple // Tech Note "UniDisk 3.5 Technical Note #3, Status call bug"
documented a bug in the SmartPort Status call.

To summarise the first part of the note, the SmartPort STATUS call does not
report WRITE PROTECT, so if an application then tries to write < 512 bytes
to an existing file on a write protected disk, the write fails and also any
attempt to close the file. Since CLOSE errors are usually ignored, the
application may reuse the buffer area resulting in further errors even if
the device is write enabled. Another symptom is when creating a file. The
CREATE call fails, of course, but it leaves the RAM copy of the allocated
block bitmap corrupted. If the device is write enabled and a file is
successful ly saved, the bitmap is written to the disk. The corruption seems
to be limited to having an extra block marked used that is not "owned" by
any file.

You should probably read the Tech Note itself. They are available online,
and I'm sure others can tell you where to find them.
--
Peter Watson
-- Write to MSDOS disks on the Apple IIgs?
-- Impossible!  ;-)