DiskSerNum()

         Returns the disk serial number

    Syntax:

         DiskSerNum( [nUnit] ) -> cSerialNumber

         nUnit : Unit number:
                 0 -> Default unit
                 1 -> A:
                 2 -> B:
                 3 -> C:
                 ...

    Description:

         Returns the serial number of the disk if it has been formatted
         with DOS 4.01 or greater.

         The default value for nUnit is 0, is that to say, if no parameters
         are given, the function returns the serial number of the default unit.

    Return:

         A character value with the disk serial number.

    Example:

         ? DiskSerNum()           //    "1A3D-66B1"