The distributed system is a collection of (P) and communication is achieved in a distributed system by (Q), where (P) and (Q) are:

Explanation

A distributed system is standardly characterised as tightly coupled software running on loosely coupled hardware: the machines are autonomous and connected only by a network (loose hardware coupling), yet the distributed operating system makes them behave to the user as one coherent system (tight software coupling). Because the processors have no physically shared memory, cooperation can only be achieved by message passing over the network. Shared memory and disk or file sharing describe tightly coupled multiprocessors or network operating systems, not a true distributed system. Note that this item is an operating-systems question that the source page files under Software Engineering.