DOS Fn 440eH: IOCTL Query Logical Drive Map

                                                         Compatibility: 3.2+ 
 Expects: AX    440eH
          BL    drive number to be used (0=default, 1=A, 2=B, etc.)
 Returns: AX    error code  if CF is set to CY
          AL    00H:     the drive has only one drive number (if no error)
                01H-1aH: the drive number currently being used to refer to
                this physical drive.
    Info: This checks to see of a physical drive is currently acting as a
          phantom floppy (or "logical drive") and if the alternate drive ID
          is currently being used.

          If CY is clear on return, then AL contains either 0 (no logical
          mappings) or AL contains the alternative drive number that can
          refer to this drive (1=A, 2=B. etc.).

   Notes: ■ If fn 440fH (set logical drive map) has not been called, all
            logical drive numbers will match the physical numbers.

          ■ The phantom floppy concept is used by DOS on systems which have
            a single diskette drive.  In that case, when you attempt to
            access drive B, DOS prompts with:

               Insert diskette for drive B.
               Press any key when ready.

            Programs may use this function to avoid using a logical ID and
            thus, avoid having DOS issue this prompt.

          ■ Phantom floppies are also created by the Driver.Sys installable
            device driver.

See Also: Fn 44H (IOCTL)
          Fn 440fH (set logical drive map)
          DOS Functions