PC/MS-DOS (INT 20h):

          Returns control to DOS

          Note: CS:0 must point to the current PSP.
          DOS 2.x provides another (and better) way to terminate a
          program: INT 21h, 4Ch

        Minix (INT 20h)
          Send/receive message

          AX = process ID of other process
          BX = pointer to message
          CX = 1 send
               2 receive
               3 send&receive

          Note: the message contains the system call number (numbered
                as in V7 Unix(tm)) and the call parameters