Server (computing)
 The inside/front of a blade server computer |
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| Common manufacturers | IBM Sun Microsystems HP Apple Inc. Intel Dell Fujitsu Siemens |
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A server is a computer program that provides services to other computer programs (and their users), in the same or other computer. The physical computer that runs a server program is also sometimes referred to as server.[1]
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Usage in information technology
In Software
Server used as an adjective, as in server operating system, refers to the product's ability to handle multiple requests, and is said to be "server-grade". A server operating system is intended or better enabled to run server applications. The differences between the server and workstation versions of a product can vary from the removal of an arbitrary software limits due to licensing, as in the case of Windows 2000, or the addition of bundled applications as in Mac OS X Server.
In Hardware
A server can also refer to a computer that has been set aside to run a specific server application. For example, when the software Apache HTTP Server is used as the web server for a company's website, the computer running Apache is also called the web server. Server applications can be divided among server computers over an extreme range, depending upon the workload.
Server is also used as a designation for computer models intended for use in running server applications under heavy workloads, also called operating units often unattended and for an extended period of time. While any workstation computer is capable of acting as a server, a server computer usually has special features intended to make it more suitable. These features can include a faster CPU, faster and more plentiful RAM, and larger hard drives. More obvious distinctions include redundancy in power supplies, network connections, and storage devices as well as the modular design of so-called Blade servers often used in server farms.
A server appliance refers to network-connected computer appliances or "appliance hardware" that provide specific, dedicated applications to a network. Use of the term appliance indicates the marriage of software and hardware in a single system that is not heavily customizable such as Google Search Appliance. Such appliances are expected to work out-of-the-box with little customization and sometimes remain the sole property of the company that produced them. The simplest appliances include switches, routers, gateways, and print servers.
Server hardware
Hardware requirements for servers vary, depending on the server application. Absolute CPU speed is not as critical to a server as it is to a desktop. Servers' duties to provide service to many users over a network lead to different requirements like fast network connections and high I/O throughput. Since servers are typically accessed over a network, servers emphasize function over form, without regard to aesthetics like appearance and noise level, because users may never lay eyes on the machine itself. Servers may accordingly run in headless mode without a monitor in order to free up processing cycles for other tasks. In general, a server becomes more specialized and therefore more efficient as unnecessary and unused services are eliminated. For this reason, many servers lack a graphical user interface, or GUI, because it consumes resources that could be allocated elsewhere. Similarly, servers often lack audio and USB interfaces.
By definition, servers provide services, but it is not always possible to predict when users will need those services. For this reason, servers are often online for weeks or months without interruption, making hardware durability extremely important. Although servers can be built from commodity computer parts, mission-critical servers use specialized hardware with low failure rates in order to maximize uptime. For example, servers may incorporate faster, higher-capacity hard drives, larger computer fans or water cooling to help remove heat, and uninterruptible power supplies that ensure the servers continue to function in the event of a power failure. These components offer higher performance and reliability at a correspondingly higher price. The dominant paradigm in servers is parallel computing, and thus high-performance servers are often placed in rack-mounted configurations to save space inside server rooms or "closets." These special rooms help mute the large amount of noise produced and also restrict physical access to the system administrators for security purposes.
Servers have a unique property in that, the more powerful and complex the system, the longer it takes for the hardware to turn on and begin loading the operating system. Servers often do extensive preboot memory testing and verification and start up of remote management services. The hard drive controllers then start up banks of drives sequentially, rather than all at once, so as not to overload the power supply, and afterwards they initiate RAID system prechecks for correct operation of redundancy. It is not uncommon for a machine to take several minutes to turn on and yet not require a restart for the next calendar year.
Server operating system
Some popular operating systems for servers — such as FreeBSD, Solaris, and Linux — are derived from or are similar to UNIX. UNIX was originally a minicomputer operating system, and as servers gradually replaced traditional minicomputers, UNIX was a logical and efficient choice of operating system for the servers. UNIX-based systems, many of which are free in both senses, are the most popular.
Server-oriented operating systems tend to have certain features in common that make them more suitable for the server environment, such as
- an optional or absent GUI,
- ability to reconfigure both hardware and software to some extent without restart,
- advanced backup facilities to permit online backups of critical data at regular and frequent intervals,
- transparent data transfer between different volumes or devices,
- flexible and advanced networking capabilities,
- automation capabilities like daemons in UNIX and services in Windows, and
- tight system security, with advanced user, resource, data, and memory protection.
Server-oriented operating systems can in many cases interact with hardware sensors to detect conditions such as overheating, processor and disk failure, and consequently alert an operator and/or take remedial measures itself.
Because the requirements of servers are, in some cases, almost diametrically opposed to those of desktop computers, it is extremely difficult to design an operating system that handles both environments well; thus, operating systems that are well suited to the desktop may not be ideal for servers and vice versa. Regardless of OS vendor, system configurations that are ideal for servers may be unsatisfactory for desktop use, and configurations that perform well on the desktop may leave much to be desired on servers. This results in many operating systems' release in both server and desktop versions. Nevertheless, the desktop versions of the Windows and Mac OS X operating systems are deployed on a minority of servers, as are some proprietary mainframe operating systems, such as z/OS. The dominant operating systems among servers are UNIX-based and open source kernel distributions.
The rise of the microprocessor-based server was facilitated by the development of Unix to run on the x86 microprocessor architecture. The Microsoft Windows family of operating systems also runs on x86 hardware, and versions beginning with Windows NT have incorporated features that making them suitable for use as server operating systems.
While the role of server and desktop operating systems remains distinct, improvements in the reliability of both hardware and operating systems have blurred the distinction between the two classes. Today, many desktop and server operating systems share similar code bases, differing mostly in configuration. The shift towards web applications and middleware platforms has also lessened the demand for specialist application servers.
Servers on the Internet
Almost the entire structure of the Internet is based upon a client-server model. High-level root nameservers, DNS servers, and routers direct the traffic on the internet. There are millions of servers connected to the Internet, running continuously throughout the world.
Among the many services provided by Internet servers are:
- the World Wide Web,
- the Domain Name System,
- e-mail,
- FTP file transfer,
- instant messaging,
- streaming audio and video, and
- online gaming.
Virtually every action taken by an ordinary Internet user requires one or more interactions with one or more servers.
There are also technologies that operate on an inter-server level.
Servers in daily life
Any computer or device serving out applications or services can technically be called a server. In an office or enterprise environment, the network server is easy to identify. A DSL/Cable modem router qualifies as a server because it provides a computer with application services like IP address assignment (via DHCP) and NAT, which is the firewall that helps protect a computer external threats. iTunes software implements a music server to stream music between computers. Many home users create shared folders and printers. Another example are the many private servers for such hosting online games such as Everquest, World of Warcraft, Counter-Strike and EVE-Online, which is currently hosted on the largest server used in the game industry.
References
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