Server

A server computer shares its resources, such as peripherals (i.e printer: print server) and file storage (i.e. disk: file server), with the users' computers, called clients, on a network. Thus, 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.

Servers are normally specialist machines developed over a couple of years to provide the reliability expected by the business users. Servers are not normally availible through high street resellers and therefore can only be purchased from branded resellers.

Small business servers start at normally £500 and range up to £50,000+ depending on spec required.

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.

The most recognized servers are:

• SUN Servers
• IBM Servers
• HP Servers
• DELL Servers

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 beneficial for server software, beginning with Windows NT. The current Windows Server version is Windows Server 2003.

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.

Source Wikipedia