a message transfer system between digital modules where two or more digital modules operate on separate and different message lengths and clock frequencies and where , temporary storage buffer holds messages being transferred between the different digital modules and acts as a speed matching and word length matching buffer unit to permit compatible transfer of message words . also , the transfer system recognizes when requests are outstanding from both digital modules and can discard a message from a requesting module . each of the two or more separate digital modules is serviced by dual system busses providing for redundancy of data transfer operations .