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. 

What is meant by DNS? What does it contain?

DNS or domain name system is a well known distributed system which is quite hierarchical in nature and is used for the following:

1. Computers
2. Services
3. Resources that are connected to some private network or internet and so on.

What does DNS contain?

- With the aid of DNS, the domain names with various participating entities contains various information. 

- A domain name system is also known as domain name service and has taken up the responsibility of resolving the queries for the above discussed domain names into the corresponding IP addresses. 

- The basic purpose of this whole process is spotting the location of devices and computer services on the World Wide Web.

- The domain name system had lately become quite an essential part of the functionality of the internet because of the world wide service it provides regarding the distributed key word based redirection. 

- To put it simply it acts as a phone book in disguise for the internet. 

- It serves as a phone book in the way that it translates the human friendly computer host names in to their corresponding IP addresses. 

For example,

The domain name: www. Abc. Com translates in to the following IP address (say): 192. 0 . 34 . 11 (IPv4) and 2630 : 0 : 2c0 : 201 : : 10 (IPv6) etc.

- Though DNS serves all the purposes of an ideal phone book in terms of the internet, it differs from the phone book in one respect which is that the DNS can be frequently updated and these updates in turn can be distributed but in phone book these tasks cannot be performed so.

- With the help of such a process the location of a particular service on a network can be easily changed without having any affect on the end users who keep on continuing with the same host name. 

-This advantage is further reaped by the users while they recite the meaningful e- mail addresses as well as the URLs (uniform resource locators) without even knowing the way via which the services are actually located by the computers. 

- With the help of domain name system, each and every domain in the network is assigned with an appropriate domain name and this domain name is mapped to corresponding IP addresses through the designation of the authoritative name servers for each and every domain. 

- These authoritative name servers hold the responsibility of their particular domains and also it helps in assigning the sub domains with their respective authoritative name servers.

- Such a mechanism has helped a lot in making the domain name system quite fault tolerant and distributed. 

- This mechanism in another way has eliminated the requirement of a single central register to be used continually for updating and consultation. 

- There is one more additional feature of the domain name system which is that the responsibility of the updating and maintenance of the master record of the domains is distributed among many domain name registrars.

- These domain name registrars are known for their competition for the domain owner’s and end user’s business. 

- The facility of moving the domains from one registrar to another has been very well provided in the domain name system.

- The technical functionality of the data base service as well as the DNS specification is also specified by the domain name system.

- This DNS protocol is a kind of detailed specification of the communication exchanges and data structures that are used in the domain name system which in turn forms a very important part of the whole internet protocol suite.