A distributed computing system consists of multiple autonomous computers that communicate through a computer network. A computer program that runs in a distributed system is called a distributed program. In distributed computing, a problem is divided into many tasks, each of which is solved by one computer. A distributed system may have a common goal, such as solving a large computational problem. Alternatively, each computer may have its own user with individual needs, and the purpose of the distributed system is to coordinate the use of shared resources or provide communication services to the users.
In a distributed system, there are several autonomous computational entities, called computers or nodes, each of which has its own local memory, and the entities communicate with each other by message passing.
There are two main reasons for using distributed systems and distributed computing. First, the very nature of the application may require the use of a communication network that connects several computers. For example, data is produced in one physical location and it is needed in another location.
Second, there are many cases in which the use of a single computer would be possible in principle, but the use of a distributed system is beneficial for practical reasons. For example, it may be more cost-efficient to obtain the desired level of performance by using a cluster of several low-end computers, in comparison with a single high-end computer. A distributed system can be more reliable than a non-distributed system, as there is no single point of failure. Moreover, a distributed system may be easier to expand and manage than a monolithic uniprocessor system.