Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!beartrk!cjp
From: cjp@beartrk.beartrack.com (CJ Pilzer)
Newsgroups: comp.sys.ibm.pc
Subject: Re: CHKDSK message
Summary: Fix of "probable non-dos" message
Keywords: disk error chkdsk
Message-ID: <398@beartrk.beartrack.com>
Date: 3 May 90 08:07:57 GMT
References: <10103@sdcc6.ucsd.edu>
Organization: Bear Track Computer Co., Takoma Park, MD.
Lines: 18


The error from CHKDSK "Probable non-DOS disk, Continue (Y/N)?" generally
is not as serious as it sounds.  There is a byte called the Media 
Descriptor Byte, located in the FAT.  When this byte becomes corrupted, you
get the non-DOS error.  Do not use the /F parameter.  If you have the
Norton Disk Doctor in the Norton utilities, it can fix the byte.  Since
you need to ask the question you probably would not br comfortable in using
a sector editor, but if you or a friend want to, check Sector 0, offset 21
of the Boot Record, Sector 1, offset 0 of the FAT 1, Offset 0 in the first
sector of FAT 2.  On a DOS hard disk this byte should be F8 hex.  On other
disks it would be different.  F9 5.25 AT floppy, FF 5.25 2 sides, 40 tracks,
and 8 sectors.  FD 5.25 2sides 40 tracks 9 sectors, and so forth.  There is a
booklet which comes with the Norton Utilities which explains some of this and
on page 108 describes a way to edit this byte.  YOU DO NOT NEED TO REFORMAT
YOUR DISK. PHEW!

I hope this helps you.  -- cj 
cjp@beartra.beartrack.com