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From: BL.JPL@forsythe.stanford.edu (Jonathan Lavigne)
Newsgroups: comp.sys.ibm.pc
Subject: Re: CHKDSK message
Message-ID: <9284@lindy.Stanford.EDU>
Date: 3 May 90 04:44:46 GMT
Sender: news@lindy.Stanford.EDU (News Service)
Distribution: usa
Lines: 44

In article <174@cms2.UUCP>,
tomf@cms2.UUCP (Tom Fortner) writes:
>In article <10103@sdcc6.ucsd.edu> ir230@sdcc6.ucsd.edu (john wavrik) writes:
>>
>>When running CHKDSK I just started getting the error message:
>>
>>               Probable non-DOS disk.
>>               Continue  (Y/N)?
>>
>John,
>        You may have lost the archive bit on your FAT file, resulting in the
>probable non-Dos disk message you received. If this is true, low level format
is the only way to restore the archive bit unless you can reconstruct the FAT
>file with PC Tools rebuild or the like.
You don't need to do a LOW-LEVEL format get rid of the "probable non-DOS disk"
message.  A DOS reformat will fix the problem -- at least it did for me when I
was getting this message a few months ago.  But, in fact, there are several
other easier ways to fix the problem.  Both Mace Utilities and version 6.0 of
PC-Tools have utilities that make the necessary correction to the FAT for you.
A couple of months ago, several people posted messages that explain how to
correct the FAT yourself using earlier versions of PC-Tools or Norton or
something similar.  Here is an explanation someone on CompuServe sent me.

------------------------------------------
#: 45742 S1/DOS/DOS Utils [S]
    18-Sep-89  19:08:32
Sb: #45388-Non-DOS Disk problem
Fm: Dave Angel 71046,1567
To: Jonathan Lavigne 70436,1272

Your 'probable non-Dos disk' error is usually caused by the first two bytes of
the FAT tables being trashed by some software.  They don't matter much anymore,
but it's a good thing to fix them, if only to keep CHKDSK happy.  (On floppies,
before 3.2, the first byte was called the FAT ID, and was used to decide
whether the disk was single sided or double, etc.   On hard disks, and more
recently on floppies too, the information is listed in the more general BPB,
contained in sector 0).

The first FAT is in sector 1, and you can find the second FAT various ways.  If
you have Norton or equivalent, let it show you how.  Anyway, the first two
bytes should be F8FF on every hard disk I've seen.

As always, be thoroughly backed up before experimenting like this.  If you
patch both copies, and if CHKDSK is happy, I'd call the operation a success.