AH = C1 on return: CF = 0 if successful = 1 if error AH = when CF set, 80h for PC & PCjr, 86h for XT (BIOS 11/8/82) ES = EBDA segment address if PS/2 - the EBDA is used internally by the PS/2 BIOS routines - the EBDA is allocated at the top of user memory by the POST routine