Q. Define Message Passing?
The PVM communication model offers asynchronous blocking receive and asynchronous blocking send and nonblocking receive functions. In our terminology blocking send returns immediately the send buffer is free for reuse and an asynchronous send doesn't depend on receiver calling a matching receive before the send can return. There are many options in PVM 3 which request that data be transferred directly from task to task. Particularly in this case if the message is large the sender can block till receiver has called a matching receive.