Int 20  - Minix - Send/receive Message                                     [O]

   AX = process ID of other process
   BX -> message
   CX = operation (1 send, 2 receive, 3 send&receive)
Program: Minix is a Version 7 Unix-compatible operating system by Andrew
     Tanenbaum

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