Date: Thu, 16 Apr 1998 17:13:19 +1200
From: physmsa AT cantua DOT canterbury DOT ac DOT nz (Mr M S Aitchison)
Subject: Re: Harddisk Question (VFAT)
To: viking AT flying-brick DOT caverock DOT co DOT nz, opendos AT delorie DOT com
Reply-to: M DOT Aitchison AT phys DOT canterbury DOT ac DOT nz
Message-id: <199804160513.RAA13512@cantua.canterbury.ac.nz>
Precedence: bulk

> From dj-admin AT delorie DOT com Thu Apr 16 16:10:17 1998
> Date: Thu, 16 Apr 1998 00:05:04 -0400 (EDT)
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> 1998/04/15/05:53:51 Re: Harddisk Question
> 
> ----------------------------------------------------------------------
> 
> Message-ID: <3533c55d DOT flying-brick AT flying-brick DOT caverock DOT net DOT nz>
> From: Eric Gillespie <viking AT flying-brick DOT caverock DOT co DOT nz>
> Can you explain what then is VFAT and whether it has been implemented in
> DR-DOS? Does it have anything to do with the Long File Name support that
> Win95 has? The reason I ask is because I tried using the LFN support, but
> decided the advantages weren't worth the hassle compared to the problems I
> ended up with - luckily I had on hand a copy of Nortons Disk Doctor and
> DiskMaster to help me clean up the disk.

VFAT is FAT with some extra (strangely-formatted) entries in the
directories for MS's idea of log file names.  It is implemented in the
OpenDOS/DRDOS optional LONGNAME TSR.

A VFAT partition appears like a normal FAT partition (same limitations
in size, etc, same partition type entry in the partition table), so it
can be used by old DOS programs and old DOS programs running under new
or old DOS versions.  What the VFAT support in Win95, DRDOS 7.0x, Linux
and OS/2 does is to create an old-style directory entry plus a
new-style entry for each file that is longer than 8+3 characters (or in
some other way needs the extra file attributes possible in VFAT, so
that means any file created using the new LFN system calls that you can
find in Ralf Brown's interrupt list).

I guess MS tried to make these "extra" directory entries invisible to
existing DOSes and their apps, but the method is strange, to say the
least.  There are good reasons to avoid using this system of long file
names (but for DRDOS and Win95 there is little other choice). These
entries have non-standard attributes, strange 16-bit character names,
use the bytes DRDOS's password bytes, and can take up many 32-byte
directory entries for each file.  Apart from many programs (like
chkdsk, disk editors, defragmenters, etc) not understanding what is
there (and so quite easily corrupting partitions), normal DOS
operations involving deleting files and creating new ones can mess up
the way the short (8+3) name is matched to a long name.

---------------------------------------------------------------------------
Mark Aitchison,               \_  Phone: +64 3 364-2947 home 337-1225
Dept of Physics & Astronomy,  </    Fax: +64 3 364-2469  or  364-2999
University of Canterbury,    /)     Web: www.phys.canterbury.ac.nz/~physmsa
Christchurch, NEW ZEALAND.  (/'  E-mail: M DOT Aitchison AT phys DOT canterbury DOT ac DOT nz
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