INT 2F U - DOS 3+ internal - GET FILE'S DRIVE
AX = 121Ah
DS:SI -> filename
Return: AL = drive (0 = default, 1 = A:, etc, FFh = invalid)
DS:SI -> filename without leading X: (if present)
SeeAlso: INT 21/AH=60h

See also: 2119

2F121A - DOS 3+ internal - GET FILE'S DRIVE