Servers
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Wikipedia-Article "Servers"
- This article is about computer servers. For 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 Internet Explorer web browser or 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.
- Over the years, the term has been misinterpreted (but in common usage now) to also mean the physical computer on which the server software runs. Software ultimately requires computer hardware to run, and originally server software would be run on a large powerful computer such as 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 These have largely been replaced by computers built using a more robust version of the microprocessor technology than is used in personal computers, and the term "server" was adopted to describe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 subsystems employing technologies such as SCSI, RAID, and PCI-X or PCI Express. It is important to note, however, that computers referred to as "servers" do not necessarily run any server software, nor is it required that server software only be run on these types of computers.
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Usage
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 client.
Server hardware
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 available through high street resellers and therefore can only be purchased from branded resellers.
Pricing for servers start as low as $700 for small, non redundant servers, while it is possible to specify a single server that costs over $100,000, applications that require this level of computing power are usually run on many smaller servers that are in a load balancing configuration.
Due to the continual demand for ever more powerful servers in ever decreasing spaces, companies such as Hewlett Packard, IBM and Dell 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 fourteen – 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 beneficial for server software, beginning with Windows NT. The current Windows Server version is Windows Server 2003. There are many servers running Linux versions such as Red Hat Linux, SUSE SLES, and Debian, which have generally proven to be more stable than Windows machines. There are an increasing number of servers running Mac OS X as organizations begin to realize the potential and stability that arises from having the hardware and software properly fitted and vetted. Most technical servers continue to be Sun, SGI, or HP workstations as they are proven and generally stable servers.
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, interacting with a human user.
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, a.k.a. PCs, by users.
See also
- Mail server
- Instant messaging server
- Web server
- FTP server
- News server
- image server
- Central ad server
- server log
- streaming media server
- sound server
- peer-to-peer
- client-server model
- History of computing hardware (1960s-present)
- CORBA
- Dedicated server