🚀 go-pugleaf

>>> 
>>> When I try to boot my 128K MAC from some disks I get a frowning face
>>> sitting on top of a 0f0064 error code on a blank screen. 
>>> Once the system is booted inserting some
>>> disks causes the error: 'this disk is unreadable to appear'.
>>> 

While working with a Lisa (MacWorks, MacXL) the following occured:
I turned the computer off. The next workday I turned it back on
and got the infamous sad mac (0f0064). After much tinkering
to determine what the disk id was (it's #4) I was able to read the
boot blocks, vol info, master directory block, try to mount it,
etc.. The reaction to MountVol was error -64 ( I think). In any case
the error meant badMDB - bad Master Directory Block.

Apparently during mounting of a volumn MountVol compares the number
of free allocation blocks in the MDB with the word value stored
in the volumn information block. If these are equal the result is
ioError = -64 (i.e. badMDB).

I solved this problem by treaking the value in the volumn info block
to the amount of free space indicated by the MDB. And voila, booted.
To be safe, I re-formated after backing up to floppy.

All this is said not to counter what has been said already, but there
are other problems. I suspect the message 'disk is unreadable' refers
to a bad MDB as a double sided disk would (I expect) result in
'not a macintosh disk' as 64K roms only know about MFS disks.

Regarding Bad drives: we had one machine (of 13) that had a bad drive.
It was replaced and the machine has worked fine since.