SERVERS

In a technical sense, a server is an instance of a computer program that accepts and responds to requests made by another program, known as a client. Less formally, any device that runs server software could be considered a server as well. Servers are used to manage network resources. For example, a user may setup a server to control access to a network, send/receive e-mail, manage print jobs, or host a website.

Some servers are committed to a specific task, often referred to as dedicated. As a result, there are a number of dedicated server categories, like print servers, file servers, network servers, and database servers. However, many servers today are shared servers which can take on the responsibility of e-mail, DNS, FTP, and even multiple websites in the case of a web server.

Because they are commonly used to deliver services that are required constantly, most servers are never turned off. Consequently, when servers fail, they can cause the network users and company many problems. To alleviate these issues, servers are commonly high-end computers setup to be fault tolerant.

Table  contain types of Server types ,its purpose and who is client.

Server type	Purpose	Clients
Application server	Hosts web apps (computer programs that run inside a web browser) allowing users in the network to run and use them, without having to install a copy on their own computers. Unlike what the name might imply, these servers need not be part of the World Wide Web;   any local network would do.	Computers with a web browser
Catalog server	Maintains an index or table of contents of information that can be found across a large distributed network, such as computers, users, files shared on file servers, and web apps. Directory servers and name servers are examples of catalog servers.	Any computer program that needs to find something on the network, such a Domain member attempting to log in, an email client looking for an email address, or a user looking for a file
Communications server	Maintains an environment needed for one communication endpoint (user or devices) to find other endpoints and communicate with them. It may or may not include a directory of communication endpoints and a presence detection service, depending on the openness and security parameters of the network	Communication endpoints (users or devices)
Computing server	Shares vast amounts of computing resources, especially CPU and random-access memory, over a network.	Any computer program that needs more CPU power and RAM than a personal computer can probably afford. The client must be a networked computer; otherwise, there would be no client–server model.
Database server	Maintains and shares any form of database (organized   collections of data with predefined properties that may be displayed in a table) over a network.	Spreadsheets, accounting software, asset management software or virtually any computer program that consumes well-organized data, especially in large volumes
Fax server	Shares one or more fax machines over a network, thus eliminating the hassle of physical access	Any fax sender or recipient
File server	Shares files and folders, storage space to hold files and folders, or both, over a network	Networked computers are the intended clients, even though local programs can be clients
Game server	Enables several computers or gaming devices to play multiplayer games	Personal computers or gaming consoles
Mail server	Makes email communication possible in the same way that a post office makes snail mailcommunication possible	Senders and recipients of email
Media server	Shares digital video or digital audio over a network through media streaming (transmitting content in a way that portions received can be watched or listened to as they arrive, as opposed to downloading an entire file and then using it)	User-attended personal computers equipped with a monitor and a speaker
Print server	Shares one or more printers over a network, thus eliminating the hassle of physical access	Computers in need of printing something
Sound server	Enables computer programs to play and record sound, individually or cooperatively	Computer programs of the same computer
Proxy server	Acts as an intermediary between a client and a server, accepting incoming traffic from the client and sending it to the server. Reasons for doing so includes content control and filtering, improving traffic performance, preventing unauthorized network access or simply routing the traffic over a large and complex network.	Any networked computer
Web server	Hosts web pages. A web server is what makes the World Wide Web possible. Each website has one or more web servers.	Computers with a web browser