On Mon, 25 Aug 2003, Feldman, Robert wrote:
  I thought /U was "unconditional", meaning
that you cannot later reverse
 the formatting and recover the previous data. Without /U, FORMAT would
 save a hidden copy of the FAT (or something like that), IIRC, making it
 easier to recover from the format. My MS-DOS 5.0 manual says that with
 the /U, FORMAT "Destroys all existing data on a disk", whatever that
 means. 
/U was also the opposite of /F, I believe.
Peace...  Sridhar