<Li> n - tier: architectures that refer typically to web applications which further forward their requests to other enterprise services . This type of application is the one most responsible for the success of application servers . </Li> <Li> Peer - to - peer: architectures where there are no special machines that provide a service or manage the network resources . Instead all responsibilities are uniformly divided among all machines, known as peers . Peers can serve both as clients and as servers . </Li> <P> Another basic aspect of distributed computing architecture is the method of communicating and coordinating work among concurrent processes . Through various message passing protocols, processes may communicate directly with one another, typically in a master / slave relationship . Alternatively, a "database - centric" architecture can enable distributed computing to be done without any form of direct inter-process communication, by utilizing a shared database . </P> <P> Reasons for using distributed systems and distributed computing may include: </P>

Explain difference between parallel system and distributed system