From: Nate Eldredge <neldredge AT hmc DOT edu>
Newsgroups: comp.games.development.programming.misc,comp.os.msdos.djgpp
Subject: Re: Disk Serial Numbers
Date: Wed, 27 Oct 1999 13:31:35 -0700
Organization: Harvey Mudd College
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To: djgpp AT delorie DOT com
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Ben Davis wrote:
> 
> This may be slightly off topic, but please bear with me...
> 
> I have noticed that some floppy disks have serial numbers; the serial number
> appears when I type 'dir/w'. Can someone confirm that the serial number of a
> floppy disk cannot be changed through software (if at all)

No, this is not true.  The serial number is written to the disk when
it's formatted (I believe it's stored in the boot sector) and so can be
modified at will.  (Assuming the disk is writable.)

>, and explain how
> to write a program which reads it? (After all, 'dir' does it, so it must be
> possible.)
> If there is a DJGPP function to do this, I would like to know. Otherwise I
> will use whatever low-level DOS Interrupts or whatever are necessary.

According to Ralf Brown's interrupt list, there's an IOCTL function to
do this.  Looks like INT 21h / AX=440Dh / minor code (in CL) = 0x66h. 
In DJGPP you can use ioctl(drive_no, DOS_GENBLKREQ, ...).
-- 

Nate Eldredge
neldredge AT hmc DOT edu