A distributed system is the collection of autonomous computers that are connected using a communication network and they communicate with each other by passing messages. The different processors have their own local memory. They use a distribution middleware. They help in sharing different resources and capabilities to provide users with a single and integrated coherent network.

Distributed computing is a field of computer science that studies distributed systems and the computer program that runs in a distributed system is called a distributed program.

A distributed system requires concurrent Components, communication network and a synchronization mechanism. A distributed system allows resource sharing, including software by systems connected to the network.

Examples of distributed systems / applications of distributed computing :

Intranets, Internet, WWW, email.

Telecommunication networks: Telephone networks and Cellular networks.

Network of branch office computers -Information system to handle automatic processing of orders,

Real-time process control: Aircraft control systems,

Electronic banking,

Airline reservation systems,

Sensor networks,

Mobile and Pervasive Computing systems.