Abstract: A multiprocessor system architecture in which two processors are each provided with an autonomous bus and the two buses can be selectively connected to each other to form a unique system bus which enables access by all processors to common memory resources connected to one of the autonomous buses. The communication between processors takes place through messages stored into mailboxes located in the common memory. The presence of a message is evidenced by a notify/interrupt signal generated by a logic unit to which each processor has access to modify and verify the logic unit's status, using the processor's autonomous bus, and without interfering with operations using the other autonomous buses of the other processor. Such verification and access does not require access to common memory resources nor polling operations to verify the status of messages stored into "mailboxes".