[WinMac] Re: Problems with PC Floppy Disks

Peter Gunn(pdg1[at]cornell.edu)
Fri, 25 Sep 1998 08:22:35 -0400

>Since moving to System 8 I have had occasional problems with copying
>files to and from PC formatted floppy disks...
>
>Has anyone else found this? Is it a documented problem

People keep saying this is not documented but I believe it most certainly
is documented (and is the main reason I bumped all my Macs up to System 8.1
from System 8.0 and 7.6). I could be giving an incorrect diagnosis, but
since no one else has even mentioned knowing about this problem, I think
its important to raise awareness.

See: http://til.info.apple.com/techinfo.nsf/artnum/n22013

which I will repeat in part below:

This appears to be an issue with PC Exchange 2.1.1, which is included in
Mac OS 7.6 and Mac OS 8, and the way some Window computers format floppy
disks.

Floppy disks that have this problem have FAT16 written to their boot
records, but these disks actually contain FAT12 directories. PC Exchange
2.1.1 reads and checks the FAT field, determines it is a FAT 16 format, and
reads the data incorrectly from the clusters on the disk. However, PC
Exchange 2.0.7, and earlier versions ignore the field in the boot record.

WARNING!
When PC Exchange 2.1.1 writes anything to a disk that contains a FAT12
format, but thinks it's a FAT16 format, it can corrupt all data on the
disk. This can happen even if the Finder creates the file, as it does when
the FINDER.DAT file is created or updated on an unlocked floppy disk for
use in Mac OS environment. Therefore, just inserting and browsing the
contents of an unlocked DOS formatted disk using Mac OS can corrupt the DOS
disk.

Not all DOS formatted floppy disks have this problem, it depends on what
was written in the boot record by the DOS computer. Two current
workarounds are:

  - to use PC Exchange 2.0.5 or 2.0.7 on systems with PC Compatibility
    Cards, which ignores the FAT16 or FAT12 field in the boot record.
  - reformat the disk as a Macintosh disk, then reformat the disk as a PC disk.

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This archive was generated by hypermail 2.0b2 on Fri Sep 25 1998 - 05:23:28 PDT