AH = 81h BX = device id CX = process id on return: CF = 0 if successful = 1 if error AH = 80h for PC & PCjr = 86h for XT (BIOS after 11/8/82) - available on the AT, XT 286, PS/2 and XT with BIOS after 11/8/82 - designed for use in simple multitasking