This article is about computer servers. For the food service use, see waiter.

In computing, a server is:

  • A computer software application that carries out some task (i.e. provides a service) on behalf of yet another piece of software called a client. In the case of the Web: An example of a server is the Apache Web Server, and an example of a client is the Mozilla Web Browser. Other server (and client) software exists for other services such as e-mail, printing, remote login, and even displaying graphical output. This is usually divided into file serving, allowing users to store and access files on a common computer; and application serving, where the software runs a computer program to carry out some task for the users. This is the original meaning of the term. Web, mail, and database servers are what most people access when using the Internet.
  • The term is now also used to mean the physical computer on which the software runs. Originally server software would be located on a mainframe computer or minicomputer. These have largely been replaced by computers built using a more robust version of the microprocessor technology than is used in personal computers, and the term "server" was adopted to describe microprocessor-based machines designed for this purpose. In a general sense, server machines have high-capacity (and sometimes redundant) power supplies, a motherboard built for durability in 24x7 operations, large quantities of ECC RAM, and fast I/O subsystem employing technologies such as SCSI, RAID, and PCI-X or PCI Express.


Sometimes this dual usage can lead to confusion, for example in the case of a web server. This term could refer to the machine which stores and operates the websites, and it is used in this sense by companies offering commercial hosting facilities. Alternatively, web server could refer to the software, such as the Apache HTTP server, which runs on such a machine and manages the delivery of web page components in response to requests from web browser clients.

Server hardware

A server computer shares its resources, such as peripherals and file storage, with the users' computers, called clients, on a network. It is possible for a computer to be a client and a server simultaneously, by connecting to itself in the same way a separate computer would.

Many new devices now come with server capabilities. The X-Internet, Web Services, and Microsoft's .NET initiative all work to make even the smallest system a server.

Many large enterprises employ numerous servers to support their needs. A collection of servers in one location is often referred to as a server farm. It is possible to configure the machines to distribute tasks so that no single machine is overwhelmed by the demands placed upon it (called load balancing), and this is often done for hosts that expect tremendous amounts of activity. The terminology can be even more confusing in this case because the client (or user) will connect to a remote host to access the server application, and that server application may need to access other server software and/or another server machine.

Due to the continual demand for ever more powerful servers in ever decreasing spaces, companies such as IBM have developed higher density configurations, the most notable of which is known as the blade server. Blade servers incorporate a number of server computers - sometimes as many as nine - each housed inside a high-density module known as a "blade", within the space typically occupied by a single computer.

Server operating systems

The rise of the microprocessor-based server was facilitated by the development of several versions of the Unix operating system to run on the Intel microprocessor architecture, including Solaris, Linux and FreeBSD. The Microsoft Windows series of operating systems also now includes server versions that support multitasking and other features required for servers, beginning with Windows NT. The current Windows Server version is Windows Server 2003.

X Window server

The X Window System can cause some confusion in the understanding of servers and clients. One might expect that the "server" in X would refer to the computer on which individual programs are running and the client to be the computer the human user is physically in front of. In reality, an X server provides access (i.e. service) to computer input and output devices, such as monitors, keyboards, and mice. Thus the X client runs on the computer doing all the internal software computation, while the X server runs on the computer that actually displays the graphical output on its monitor, and which the human user is sitting in front of.

The X Window System (which speaks the X protocol) is able to operate over a network, because it is designed to be client/server based. The only requirement for a client to connect to a server is a network connection. However, in most situations, the server and clients run on the same physical machine. In this case, either UNIX local sockets or a loopback interface act as transparent media for network connections between client and server.

Historical note

Mainframes and minicomputers were originally accessed using dumb terminals, which were unable to carry out any significant processing. This largely ended with the widespread use of personal computers by users.

See also

External links

cs:Server da:Server de:Server es:Servidor informtico eo:Servilo fr:Serveur informatique ko:서버 he:שרת hu:Kiszolgl lt:Serveris nl:Server ja:サーバ no:Tjener pl:Serwer pt:Servidor ru:Сервер simple:Server fi:Palvelin zh:服务器


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