In distributed systems, inter-process communication is very important. In non-distributed systems the message passing occurs in the stored memory. However, this is not how it is done in distributed systems. Here, communication is based on primitive low-level message passing as done by the underlying network. Modern distributed systems have a large number(millions) of processes that are taking place at any instant of time. Thus dedicated systems for message passing between different computers have been created. These dedicated systems are:
1. Remote Procedure Call (RPC)
2. Message Oriented Middleware (MOM)
3. Publish Subscribe (Pub-Sub)