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Server (computing)
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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 often referred to as server.
Services can be supplied centrally by the use of a server; in other cases all the machines on a network have the same status with no dedicated server, and services are supplied peer-to-peer.
erver 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".
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Encyclopedia
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 often referred to as server.
Services can be supplied centrally by the use of a server; in other cases all the machines on a network have the same status with no dedicated server, and services are supplied peer-to-peer.
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 usually as critical to a server as it is to a desktop machine. 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 usually accessed over a network they may run in headless mode without a monitor or input device. Processes which are not needed for the server's function are not used. Many servers do not have a graphical user interface (GUI) as it is unnecessary and consumes resources that could be allocated elsewhere. Similarly, audio and USB interfaces may be omitted.
Servers often run for long periods without interruption and availability must often be very high, making hardware reliability and 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. Hardware redundancy—installing more than one instance of modules such as power supplies and hard disks arranged so that if one fails another is automatically available—is widely used. ECC memory devices which detect and correct errors are used; non-ECC memory can cause data corruption.
Servers are often rack-mounted and situated in server rooms for convenience and to restrict physical access for security.
Many servers take a long time for the hardware to start up and load the operating system. Servers often do extensive preboot memory testing and verification and startup 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 with startup surges, and afterwards they initiate RAID system prechecks for correct operation of redundancy. It is not uncommon for a machine to take several minutes to start up, but it may not need restarting for months or years.
Server operating systems
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 operating systems, many of which are free in both senses, are popular.
Server-oriented operating systems tend to have certain features in common that make them more suitable for the server environment, such as
- GUI not available or optional,
- ability to reconfigure and update both hardware and software to some extent without restart,
- advanced backup facilities to permit regular and frequent online backups of critical data,
- transparent data transfer between different volumes or devices,
- flexible and advanced networking capabilities,
- automation capabilities such as 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 servers must supply a restricted range of services to perhaps many users while a desktop computer must carry out a wide range of functions required by its user, the requirements of an operating system for a server are different from those of a desktop machine. While it is possible for an operating system to make a machine both provide services and respond quickly to the requirements of a user, it is usual to use different operating systems on servers and desktop machines. Some operating systems are supplied in both server and desktop versions with similar user interface.
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 since Windows NT have been available in versions suitable for server use.
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:
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. Other services do not use dedicated servers; for example peer-to-peer file sharing, some implementations of telephony (e.g., Skype), and supplying television programs to several users (e.g., Kontiki).
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 from 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 servers for such hosting online games such as Everquest, World of Warcraft, Counter-Strike and EVE-Online.
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