Re: [WinMac] Problems with PC Floppy Disks

TOM LEAHEY(Thomas.J.Leahey[at]maf.nasa.gov)
25 Sep 1998 10:15:05 -0500

Hi all,

    This is my first post to this list. I've been lurking for some 3 weeks now
and have found it a useful read (I do tech support in a mixed-environment shop).
Regarding the recent thread of posts about problems with the lastest PC Exchange
and floppies, I thought I'd pass along info that I think may be related. Apple
released an special utility for PC Exchange 2.1.1 users (MacOS8.1?) back in July
of this year. It's called DOS Format Fixer. Here's the info from the ReadMe
file:

--------------------------------------------------------------------------------
DOS Format Fixer 1.0

DOS Format Fixer 1.0 is a utility that corrects format information on some DOS
format floppy disks for use with PC Exchange 2.1.1 (referred to as PC Exchange
in this update). The DOS Format Fixer 1.0 will prevent some kinds of corruption.
If you have a floppy disk that is already damaged, DOS Format Fixer 1.0 will not
repair the damage.

Floppy disks formatted with Windows 3.1 or DOS 5.0 can experience data
corruption when they are used on a Macintosh with PC Exchange. This problem is
resolved in PC Exchange 2.2, which is included with Mac OS 8.1. If you are
using Mac OS 8.0, you can download the Mac OS 8.1 Update for free. If you are
using Mac OS 7.6 or Mac OS 7.6.1, you can use the DOS Format Fixer 1.0 to avoid
the problem.

Technical Information
Certain floppy disks have erroneous information written to the first sector.
Floppy disks normally have a 12-bit file allocation table (FAT), but the problem
floppy disks have "FAT16" written to the first sector. This indicates to PC
Exchange that the floppy disk should have a 16-bit FAT when it actually has a
12-bit FAT. This causes PC Exchange to incorrectly read the FAT and PC Exchange
subsequently may either overwrite data in used sectors or read data from the
wrong sectors. The DOS Format Fixer 1.0 changes the data on the first sector of
the floppy disk. It replaces "FAT16" with "FAT12" so PC Exchange will now treat
the floppy disk as having a 12-bit FAT.

Follow the steps below to use DOS Format Fixer 1.0. It is recommended that you
check your floppy disks using Scandisk or some other disk repair utility in DOS
or Windows first, as the DOS Format Fixer 1.0 does not repair floppy disks that
have already been corrupted.

1. Turn off PC Exchange by opening the PC Exchange control panel and clicking
    the "Off" button.

2. Open DOS Format Fixer 1.0. A message will remind you to turn off PC Exchange.
Click OK.

3. Make sure DOS Format Fixer 1.0 is the active application.

4. Insert each floppy disk you wish to fix. DOS Format Fixer 1.0 will correct
the first
    sector on the floppy disk and then eject it.

5. After all floppy disks have been fixed, quit DOS Format Fixer 1.0.

6. Turn PC Exchange back on.

You will now be able to use the floppy disks with any version of PC Exchange.
-----------------------------------------------------------------------------

    My thoughts are that maybe this FAT12 vs. FAT16 thing, which seems to be
ignored on PCs (!) and older versions of PC Exchange may be the culprit some of
you are encountering. Maybe not. But I thought it'd be useful to pass along.
I'd expect the probelm to be fixed in the version of PC Exchange that comes with
the upcoming MacOS 8.5 scheduled to ship this Oct 17th.

Tom Leahey
tom.leahey@maf.nasa.gov

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This archive was generated by hypermail 2.0b2 on Fri Sep 25 1998 - 08:23:34 PDT