Int 21 Fn 4456  U - Dr-dos 5.0+ - History Buffer Control                   [O]

   AX = 4456h
   DL = flag
       bit 0: 1 = COMMAND.COM history buffers
          0 = set to application

Return: AL = ??? (20h if DL bit 0 set, A0h if clear (DR-DOS 6.0))

Note:  This was seen called by COMMAND.COM of DR-DOS 6.0