[techtalk] request for ideas

Karl-Heinz Zimmer khz at snafu.de
Mon Oct 11 20:16:08 EST 1999


Am 10/11/99, 10:40:25 PM, schrieb Kelly Lynn Martin:

> On Mon, 11 Oct 1999 14:47:03 -0500, Aaron Malone
> <aaron at mancala.semo.net> said:

> >Actually, you *do* have to tell Win/DOS that you've inserted
> >a floppy drive.  You do so by typing "a:" then running
> >commands, or by double-clicking on the "3 1/2 Floppy (A:)"
> >icon.  The advantage in this is that the actual mounting is
> >transparent to the user.

> More accurately, DOS "mounts" the floppy drive every time it
> accesses it.  Very inefficient.

Even more: very dangerous!   :-)

Why that?

Because good(?) old DOS (Win 9x resp.) does things that you do
not know about and so it might destroy your data without you
having typed anything wrong.

I am not kidding:

Several years ago (in my bad old DOS times) i used to tell all
my friends, students as well as teachers never (never!) to write

DIR A:

after just having changed the floppy.

Instead of doing so i told them to type like this:

A:
DIR
C:

What's the difference?

Very simply: the first 'A:' causes the OS to *mount* the floppy,
the second 'DIR' is the synonym to the 'ls' command, the third
'C:' sets the current directory back to the harddisk.

So what would happen when typing 'DIR A:' instead of this?

Very smart DOS (Win 9x resp.) will notice that you want to see
the directory listing of a floppy in A:.

Normal PC floppy drives have a nice feature called 'media
change detection' that sets a flag to be viewed by DOS.

Often (often!) this feature is out of order and does *not* set
the flag when a floppy was changed.

Now good(?) old DOS (Win 9x resp.) comes and wants to list the
floppy's directory.  It does *not* find the 'media changed' flag
and therefor thinks that the old floppy is still in the drive.

When reading the directory DOS notices that the contents are
defferent from what it has in the cache.  (Cache was filled
with data when accessing the drive before.)  So smart DOS does
some very nice thing: *without* asking the user it overwrites
the contents of the disk.  The cached directory contents are
written just over the *real* directory structure because DOS
tries to 'repair' the supposedly damaged directory.

Needless to say that you will need a Hex Browser on a per-sector
basis to get your data from that floppy!  :-(

This is not a fantasy story of mine but did really happen and
things like this were the reason why i erased *all* MS software
on my home PC two years ago.

It's fine to have to click on a symbol on KDE for mounting your
floppy and it's fine to have to write a short command on the
command line: by doing so *you* know what is happening and the
OS does know that you *really* did change the medium: far better
than to trust an auto-detection feature that is nonworking.

'But Moses supposes erroneously' is fine for comedian songs,
not for a so called 'operating system'.

Best greetings,

Karl-Heinz
-- 
K.-H. Zimmer     *     Hamburg     *     Germany




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