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)
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DOS Fn 440eH: IOCTL Query Logical Drive Map