This is achieved in a computer system employing a multiple facility operating system architecture. The computer system includes a plurality of processor units for implementing a predetermined set of peer-level facilities wherein each peer-level facility includes a plurality of related functions and a communications bus for interconnecting the processor units. Each of the processor units includes a central processor and the stored program that, upon execution, provides for the implementation of a predetermined peer-level facility of the predetermined set of peer-level facilities, and for performing a multi-tasking interface function. The multi-tasking interface function is responsive to control messages for selecting for execution functions of the predetermined peer-level facility and that is responsive to the predetermined peer-level facility for providing control messages to request or to respond to the performance of functions of another peer-level facility of the computer system. The multi-tasking interface functions of each of the plurality of processor units communicate among one another via the network bus.