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In computing, a server is a piece of computer hardware or software (computer program) that provides functionality for other programs or devices, called "clients". This architecture is called the client–server model. Servers can provide various functionalities, often called "services", such as sharing data or resources among multiple clients, or performing computation for a client. A single server can serve multiple clients, and a single client can use multiple servers. A client process may run on the same device or may connect over a network to a server on a different device.[1] Typical servers are database servers, file servers, mail servers, print servers, web servers, game servers, and application servers.[2]

Client–server systems are today most frequently implemented by (and often identified with) the request–response model: a client sends a request to the server, which performs some action and sends a response back to the client, typically with a result or acknowledgment. Designating a computer as "server-class hardware" implies that it is specialized for running servers on it. This often implies that it is more powerful and reliable than standard personal computers, but alternatively, large computing clusters may be composed of many relatively simple, replaceable server components.

A server farm or server cluster is a collection of computer servers maintained by an organization to supply server functionality far beyond the capability of a single device. Modern data centers are now often built of very large clusters of much simpler servers,data centers are now often built of very large clusters of much simpler servers,[11] and there is a collaborative effort, Open Compute Project around this concept.

Appliances

A class of small specialist servers called network appliances are generally at the low end of the

A class of small specialist servers called network appliances are generally at the low end of the scale, often being smaller than common desktop computers.

Mobile

A mobile

A mobile server has a portable form factor, e.g. a laptop.[12] In contrast to large data centers or rack servers, the mobile server is designed for on-the-road or ad hoc deployment into emergency, disaster or temporary environments where traditional servers are not feasible due to their power requirements, size, and deployment time.[13] The main beneficiaries of so-called "server on the go" technology include network managers, software or database developers, training centers, military personnel, law enforcement, forensics, emergency relief groups, and service organizations.[14] To facilitate portability, features such as the keyboard, display, battery (uninterruptible power supply, to provide power redundancy in case of failure), and mouse are all integrated into the chassis.

Operating systems

In 2010, data centers (servers, cooling, and other electrical infrastructure) were responsible for 1.1-1.5% of electrical energy consumption worldwide and 1.7-2.2% in the United States.[17] One estimate is that total energy consumption for information and communications technology saves more than 5 times its carbon footprint[18] in the rest of the economy by increasing efficiency.

Global energy consumption is increasing due to the increasing demand of data and bandwidth. Natural Resources Defense Council (NRDC) states that data centers used [17] One estimate is that total energy consumption for information and communications technology saves more than 5 times its carbon footprint[18] in the rest of the economy by increasing efficiency.

Global energy consumption is increasing due to the increasing demand of data and bandwidth. Natural Resources Defense Council (NRDC) states that data centers used Natural Resources Defense Council (NRDC) states that data centers used 91 billion kilowatt hours (kWh) electrical energy in 2013 which accounts to 3% of global electricity usage.

Environmental groups have placed focus on the carbon emissions of data centers as it accounts to 200 million metric tons of carbon dioxide in a year.

Various hosting providers have introduced eco-friendly servers that reduced carbon emissions by 80% through off-shelf equipment and energy management.