Re: Read PC 720k Floopy on Apple IIe?

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

"David Empson" <dempson@actrix.gen.nz> wrote in message 
1ht539u.ezszz95vsnpjN%dempson@actrix.gen.nz">news:1ht539u.ezszz95vsnpjN%dempson@actrix.gen.nz...
> My recollection is that the Superdrive card gets confused after you
> access a 720K disk in a Superdrive. If you subsequently try to format a
> double density disk as 800K, it actually formats it at 720K but the
> software doesn't know this happened so you get a bad disk. A similar
> problem happens if you try to format a 720K disk after accessing an 800K
> one.

Here are some notes I wrote in the "Known Problems" section in the MUG! 
Readme file many years ago. I remember the problem, but not a lot of the 
details any more. (David's comments also ring bells, and both problems may 
well be related.)
=========================
Apple's 3.5" Disk Controller seems to have a problem when it does a 
low-level format on a double-density MFM disk (ie. 720K). The format process 
actually completes, and the system doesn't crash, but you can no longer 
access *any* 3.5" disks! You must eject the disk and do a 
'three-finger-salute' reboot (a normal shutdown does not seem to be enough), 
after which you can finish the original operation. For example, 'Diskcopy' 
will format the target disk if it is unformatted or the wrong size (eg. 
800K). After the format, the program fails as described above, but after 
rebooting the copy proceeds as the disk is now formatted. 'Format' similarly 
fails after the low-level format, but after rebooting you can use the 'Quick 
format' option to write the empty directory, etc. Note that this format 
problem can be seen with other programs, not just MUG!

The problem *DOES NOT* occur with 1.44Mb (high-density) disks - this is not 
really surprising as they are already MFM-formatted for both Apple and MSDOS 
use. Note that 'Diskcopy' will copy 720K disks just fine if the target disk 
has previously been formatted for 720K.
=========================
-- 
Peter Watson
-- Write to MSDOS disks on the Apple IIgs?
-- Impossible!  ;-)