Int 2F Fn 122C  U - Dos 3.3+ Internal - Get Device Chain                   [D]

   AX = 122Ch

Return: BX:AX -> header of second device driver (NUL is first) in driver chain

Note:  although this function exists in DR DOS 5.0 and Novell DOS 7, it
     always returns 0000h:0000h prior to Novell DOS 7 Update 15

See Also: INT 21/AH=52h