The goal of communication in Mach is to support a variety of styles of communication in a reliable and flexible way (Draves, 1990). It can handle asynchronous message passing, RPC, byte streams, and other forms as well. Mach's interprocess communication mechanism is based on that of its ancestors, RIG and Accent. Due to this evolution, the mechanism used has been optimized for the local case (one node) rather than the remote case (distributed system).

We will first explain the single-node case in considerable detail, and then come back to how it has been extended for networking. It should be noted that in these terms, a multiprocessor is a single node, so communication between processes on different CPUs within the same multiprocessor uses the local case.