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Tuesday, May 14, 2013

What is a Distributed System?

In the field of computer science, the distributed computing constitutes of distributed systems. 
- Multiple computers that are capable of communicating via a computer network together compose a distributed system. 
- All the computers in a distributed system work together in order to accomplish a common task.
- A common program is also required for running this whole system and is known as the distributed system. 
- Such programs for distributed systems are written using the process called the distributed programming. 
- Distributed computing involves the use of distributed systems for solving the computational problems.
- A distributed system divides the problem into much smaller tasks that are then given to one or more computers of the distributed systems. 
- These systems use message passing for communicating with each other. 
- The term distributed system earlier referred to the networks which had their hosts distributed over a geographical area. 
- This term was eventually refined and now is applied to a much broader concept. 
- It now also refers to the various autonomous processes that execute on the same system but maintain an interaction with other systems also through message passing. 
Because of the wide sense to which the concept is applied, it has no formal definition; rather the following properties are used for defining it:
  1. There are many computational entities of the distributed system that are autonomous in nature and each of them possesses individual local memory. These entities are commonly referred to as the nodes.
  2. By means of message passing these entities communicate with each other.
- A distributed system works towards a common goal which may involve solving a big computing problem. 
- On the other side, each node in a distributed system may have its own requirements. 
- The distributed system must provide communication means to the user and help in coordinating the use of the common resources.

Properties of Distributed Systems

Distributed systems possess many other typical properties as mentioned below:
  1. It has the capability to tolerate the failures of the individual nodes or the computers.
  2. The system’s structure cannot be determined in advance. It includes a number of factors such as number of computers, network topology, and network latency and so on. The computers in the system might be of many different types and so the links also. As a result the structure of a distributed system may alter while executing a distributed program.
  3. The complete view of the distributed system is hidden from its nodes. They are provided only with a limited view or information about the system. Only a part of the input is known by each of the nodes.
- There are two terms which consistently overlap with the distributed computing namely parallel computing and concurrent computing
- The distinctions between these three are not clear at all. 
- At the same time a system may be called both a parallel one and a distributed one.
- Another thing about distributed systems is that the processors involved run in concurrence with each other but in parallel.
- Distributed computing in a more tightly coupled form is called parallel computing. 
- Thus, a loosely coupled form of parallel computing is the distributed computing. 

Two main reasons have been observed for using distributed computing:
  1. Depending on the nature of the application it may require using a network connecting many other systems. For example, data produced by one system is required by others.
  2. There are cases, where by theory and principle use of a single computer is possible but for the same case if a distributed system is used in practical then it might be more beneficial. For example, using a cluster of low – end computers for attaining the desired level of performance might be more cost efficient. 

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