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Server (computing)
Encyclopedia
Client (computing)
A client is an application or system that accesses a service made available by a server. The server is often on another computer system, in which case the client accesses the service by way of a network....
". Thus, the "server" performs some computational task on behalf of "clients". The clients either run on the same computer or connect through the network.
In most common use, server is a physical computer (a hardware
Hardware
Hardware is a general term for equipment such as keys, locks, hinges, latches, handles, wire, chains, plumbing supplies, tools, utensils, cutlery and machine parts. Household hardware is typically sold in hardware stores....
system) dedicated to running one or more such services (as a host
Host (network)
A network host is a computer connected to a computer network. A network host may offer information resources, services, and applications to users or other nodes on the network. A network host is a network node that is assigned a network layer host address....
), to serve the needs of users of the other computers on the network. Depending on the computing service that it offers it could be a database server
Database server
A database server is a computer program that provides database services to other computer programs or computers, as defined by the client–server model. The term may also refer to a computer dedicated to running such a program...
, file server
File server
In computing, a file server is a computer attached to a network that has the primary purpose of providing a location for shared disk access, i.e. shared storage of computer files that can be accessed by the workstations that are attached to the computer network...
, mail server, print server
Print server
A print server, or printer server, is a device that connects printers to client computers over a network. It can accept print jobs from the computers and send the jobs to the appropriate printers....
, web server
Web server
Web server can refer to either the hardware or the software that helps to deliver content that can be accessed through the Internet....
, or other.
In the context of Internet Protocol
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
(IP) networking, a server is a program that operates as a socket
Internet socket
In computer networking, an Internet socket or network socket is an endpoint of a bidirectional inter-process communication flow across an Internet Protocol-based computer network, such as the Internet....
listener.
Servers often provide essential services across a network, either to private users inside a large organization or to public users via the Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
. For example, when you enter a query in a search engine, the query is sent from your computer over the internet to the servers that store all the relevant web pages. The results are sent back by the server to your computer.
Usage
The term server is used quite broadly in information technologyInformation technology
Information technology is the acquisition, processing, storage and dissemination of vocal, pictorial, textual and numerical information by a microelectronics-based combination of computing and telecommunications...
. Despite the many server-branded products available (such as server versions of hardware, software or operating systems), in theory any computerised process that shares a resource to one or more client processes is a server. To illustrate this, take the common example of file sharing
File sharing
File sharing is the practice of distributing or providing access to digitally stored information, such as computer programs, multimedia , documents, or electronic books. It may be implemented through a variety of ways...
. While the existence of files on a machine does not classify it as a server, the mechanism which shares these files to clients by the operating system is the server.
Similarly, consider a web server application (such as the multiplatform "Apache HTTP Server
Apache HTTP Server
The Apache HTTP Server, commonly referred to as Apache , is web server software notable for playing a key role in the initial growth of the World Wide Web. In 2009 it became the first web server software to surpass the 100 million website milestone...
"). This web server software can be run on any capable computer
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...
. For example, while a laptop
Laptop
A laptop, also called a notebook, is a personal computer for mobile use. A laptop integrates most of the typical components of a desktop computer, including a display, a keyboard, a pointing device and speakers into a single unit...
or personal computer is not typically known as a server, they can in these situations fulfill the role of one, and hence be labelled as one. It is in this case that the machine's purpose as a web server
Web server
Web server can refer to either the hardware or the software that helps to deliver content that can be accessed through the Internet....
classifies it in general as a server.
In the hardware sense, the word server typically designates computer models intended for hosting software applications under the heavy demand of a network
Computer network
A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....
environment. In this client–server configuration one or more machines, either a computer or a computer appliance
Computer appliance
A computer appliance is generally a separate and discrete hardware device with integrated software , specifically designed to provide a specific computing resource. These devices became known as "appliances" because of their similarity to home appliances, which are generally "closed and sealed" –...
, share information with each other with one acting as a host
Host (network)
A network host is a computer connected to a computer network. A network host may offer information resources, services, and applications to users or other nodes on the network. A network host is a network node that is assigned a network layer host address....
for the other.
While nearly any personal computer
Personal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
is capable of acting as a network server, a dedicated server will contain features making it more suitable for production environments. These features may include a faster CPU
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
, increased high-performance RAM
Ram
-Animals:*Ram, an uncastrated male sheep*Ram cichlid, a species of freshwater fish endemic to Colombia and Venezuela-Military:*Battering ram*Ramming, a military tactic in which one vehicle runs into another...
, and typically more than one large hard drive. More obvious distinctions include marked redundancy
Redundancy (engineering)
In engineering, redundancy is the duplication of critical components or functions of a system with the intention of increasing reliability of the system, usually in the case of a backup or fail-safe....
in power supplies
Power supply
A power supply is a device that supplies electrical energy to one or more electric loads. The term is most commonly applied to devices that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy to electrical energy...
, network connections, and even the servers themselves.
Between the 1990s and 2000s an increase in the use of dedicated hardware saw the advent of self-contained server appliances. One well-known product is the Google Search Appliance
Google Search Appliance
The Google Search Appliance is a rack-mounted device providing document indexing functionality that can be integrated into an intranet, document management system or web site using a Google search-like interface for end-user retrieval of results. The operating system is based on CentOS...
, a unit that combines hardware and software in an out-of-the-box packaging. Simpler examples of such appliances include switches
Network switch
A network switch or switching hub is a computer networking device that connects network segments.The term commonly refers to a multi-port network bridge that processes and routes data at the data link layer of the OSI model...
, routers, gateways
Residential gateway
A residential gateway is a home networking device, used as a gateway to connect devices in the home to the Internet or other WAN.It is an umbrella term, used to cover multi-function networking computer appliances used in homes, which may combine a DSL or cable modem, a firewall, a consumer-grade...
, and print server
Print server
A print server, or printer server, is a device that connects printers to client computers over a network. It can accept print jobs from the computers and send the jobs to the appropriate printers....
, all of which are available in a near plug-and-play
Plug-and-play
In computing, plug and play is a term used to describe the characteristic of a computer bus, or device specification, which facilitates the discovery of a hardware component in a system, without the need for physical device configuration, or user intervention in resolving resource conflicts.Plug...
configuration.
Modern operating systems such as Microsoft Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
or Linux distributions rightfully seem to be designed with a client–server architecture in mind. These operating systems attempt to abstract hardware
Hardware abstraction
Hardware abstractions are sets of routines in software that emulate some platform-specific details, giving programs direct access to the hardware resources....
, allowing a wide variety of software to work with components of the computer. In a sense, the operating system can be seen as serving hardware to the software, which in all but low-level programming language
Low-level programming language
In computer science, a low-level programming language is a programming language that provides little or no abstraction from a computer's instruction set architecture. Generally this refers to either machine code or assembly language...
s must interact using an API.
These operating systems may be able to run programs in the background called either service
Windows Service
On Microsoft Windows operating systems, a Windows service is a long-running executable that performs specific functions and which is designed not to require user intervention. Windows services can be configured to start when the operating system is booted and run in the background as long as...
s or daemon
Daemon (computer software)
In Unix and other multitasking computer operating systems, a daemon is a computer program that runs as a background process, rather than being under the direct control of an interactive user...
s. Such programs may wait in a sleep state
Sleep (operating system)
A computer program may sleep, which places it into an inactive state for a period of time. Eventually the expiration of an interval timer, or the receipt of a signal or interrupt causes the program to resume execution.- Usage :...
for their necessity to become apparent, such as the aforementioned Apache HTTP Server software. Since any software that provides services can be called a server, modern personal computers can be seen as a forest of servers and clients operating in parallel
Parallel computing
Parallel computing is a form of computation in which many calculations are carried out simultaneously, operating on the principle that large problems can often be divided into smaller ones, which are then solved concurrently . There are several different forms of parallel computing: bit-level,...
.
The Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
itself is also a forest of servers and clients. Merely requesting a web page
Web page
A web page or webpage is a document or information resource that is suitable for the World Wide Web and can be accessed through a web browser and displayed on a monitor or mobile device. This information is usually in HTML or XHTML format, and may provide navigation to other web pages via hypertext...
from a few kilometers away involves satisfying a stack of protocols that involve many examples of hardware and software servers. The least of these are the router
Router
A router is a device that forwards data packets between computer networks, creating an overlay internetwork. A router is connected to two or more data lines from different networks. When a data packet comes in on one of the lines, the router reads the address information in the packet to determine...
s, modem
Modem
A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
s, domain name servers, and various other servers necessary to provide us the world wide web
World Wide Web
The World Wide Web is a system of interlinked hypertext documents accessed via the Internet...
.
Server hardware
Computer hardware
Personal computer hardware are component devices which are typically installed into or peripheral to a computer case to create a personal computer upon which system software is installed including a firmware interface such as a BIOS and an operating system which supports application software that...
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 such as fast network connections and high I/O throughput. Since servers are usually accessed over a network, they may run in headless
Headless system
A headless system is a computer system or device that has been configured to operate without a monitor , keyboard and mouse...
mode without a monitor or input device. Processes that are not needed for the server's function are not used. Many servers do not have a graphical user interface
Graphical user interface
In computing, a graphical user interface is a type of user interface that allows users to interact with electronic devices with images rather than text commands. GUIs can be used in computers, hand-held devices such as MP3 players, portable media players or gaming devices, household appliances and...
(GUI) as it is unnecessary and consumes resources that could be allocated elsewhere. Similarly, audio and USB
Universal Serial Bus
USB is an industry standard developed in the mid-1990s that defines the cables, connectors and protocols used in a bus for connection, communication and power supply between computers and electronic devices....
interfaces may be omitted.
Servers often run for long periods without interruption and availability
Availability
In telecommunications and reliability theory, the term availability has the following meanings:* The degree to which a system, subsystem, or equipment is in a specified operable and committable state at the start of a mission, when the mission is called for at an unknown, i.e., a random, time...
must often be very high, making hardware reliability and durability extremely important. Although servers can be built from commodity computer parts, mission-critical enterprise servers are ideally very fault tolerant and use specialized hardware with low failure rate
Failure rate
Failure rate is the frequency with which an engineered system or component fails, expressed for example in failures per hour. It is often denoted by the Greek letter λ and is important in reliability engineering....
s in order to maximize uptime
Uptime
Uptime is a measure of the time a machine has been up without any downtime.It is often used as a measure of computer operating system reliability or stability, in that this time represents the time a computer can be left unattended without crashing, or needing to be rebooted for administrative or...
, for even a short-term failure can cost more than purchasing and installing the system. For example, it may take only a few minutes of down time at a national stock exchange
Stock exchange
A stock exchange is an entity that provides services for stock brokers and traders to trade stocks, bonds, and other securities. Stock exchanges also provide facilities for issue and redemption of securities and other financial instruments, and capital events including the payment of income and...
to justify the expense of entirely replacing the system with something more reliable. Servers may incorporate faster, higher-capacity hard drives, larger computer fan
Computer fan
A computer fan is any fan inside, or attached to, a computer case used for cooling purposes, and may refer to fans that draw cooler air into the case from the outside, expel warm air from inside, or move air across a heatsink to cool a particular component...
s or water cooling to help remove heat, and uninterruptible power supplies
Uninterruptible power supply
An uninterruptible power supply, also uninterruptible power source, UPS or battery/flywheel backup, is an electrical apparatus that provides emergency power to a load when the input power source, typically mains power, fails...
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
Redundancy (engineering)
In engineering, redundancy is the duplication of critical components or functions of a system with the intention of increasing reliability of the system, usually in the case of a backup or fail-safe....
—installing more than one instance of modules such as power supplies
Power supply
A power supply is a device that supplies electrical energy to one or more electric loads. The term is most commonly applied to devices that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy to electrical energy...
and hard disk
Hard disk
A hard disk drive is a non-volatile, random access digital magnetic data storage device. It features rotating rigid platters on a motor-driven spindle within a protective enclosure. Data is magnetically read from and written to the platter by read/write heads that float on a film of air above the...
s arranged so that if one fails another is automatically available—is widely used. ECC memory devices that detect and correct errors are used; non-ECC memory is more likely to cause data corruption.
To increase reliability, most of the servers use memory with error detection and correction
ECC memory
Error-correcting code memory is a type of computer data storage that can detect and correct the more common kinds of internal data corruption...
, redundant disks
RAID
RAID is a storage technology that combines multiple disk drive components into a logical unit...
, redundant power supplies and so on. Such components are also frequently hot swappable, allowing technicians to replace them on the running server without shutting it down. To prevent overheating, servers often have more powerful fans. As servers are usually administered by qualified engineers, their operating systems are also more tuned for stability and performance than for user friendliness and ease of use, Linux taking noticeably larger percentage than for desktop computers.
As servers need stable power supply, good Internet access, increased security and are also noisy, it is usual to store them in dedicated server centers or special rooms. This requires reducing the power consumption, as extra energy used generates more heat thus causing the temperature in the room to exceed the acceptable limits; hence normally, server rooms are equipped with air conditioning devices. Server casings are usually flat and wide, adapted to store many devices next to each other in server rack. Unlike ordinary computers, servers usually can be configured, powered up and down or rebooted remotely, using out-of-band management
Out-of-band management
In computing, out-of-band management involves the use of a dedicated management channel for device maintenance...
.
Many servers take a long time for the hardware to start up and load the operating system. Servers often do extensive pre-boot
Preboot Execution Environment
The Preboot eXecution Environment is an environment to boot computers using a network interface independently of data storage devices or installed operating systems.PXE was introduced as part of the Wired for Management framework by Intel and is described in the specification The Preboot...
memory testing and verification and startup of remote management services. The hard drive controllers
Disk controller
The disk controller is the circuit which enables the CPU to communicate with a hard disk, floppy disk or other kind of disk drive.Early disk controllers were identified by their storage methods and data encoding. They were typically implemented on a separate controller card...
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
RAID
RAID is a storage technology that combines multiple disk drive components into a logical unit...
system pre-checks for correct operation of redundancy. It is common for a machine to take several minutes to start up, but it may not need restarting for months or years.
Server operating systems
Server-oriented operating systems tend to have certain features in common that make them more suitable for the server environment, such as- GUIGuiGui or guee is a generic term to refer to grilled dishes in Korean cuisine. These most commonly have meat or fish as their primary ingredient, but may in some cases also comprise grilled vegetables or other vegetarian ingredients. The term derives from the verb, "gupda" in Korean, which literally...
not available or optional - ability to reconfigureReconfigurable computingReconfigurable computing is a computer architecture combining some of the flexibility of software with the high performance of hardware by processing with very flexible high speed computing fabrics like field-programmable gate arrays...
and update both hardware and software to some extent without restart, - advanced backupBackupIn information technology, a backup or the process of backing up is making copies of data which may be used to restore the original after a data loss event. The verb form is back up in two words, whereas the noun is backup....
facilities to permit regular and frequent online backups of critical dataDataThe term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...
, - transparentTransparency (computing)Any change in a computing system, such as new feature or new component, is transparent if the system after change adheres to previous external interface as much as possible while changing its internal behaviour. The purpose is to shield from change all systems on the other end of the interface...
data transfer between different volumesVolume (computing)In the context of computer operating systems, volume is the term used to describe a single accessible storage area with a single file system, typically resident on a single partition of a hard disk. Similarly, it refers to the logical interface used by an operating system to access data stored on...
or devices, - flexible and advanced networking capabilities,
- automation capabilities such as daemonsDaemon (computer software)In Unix and other multitasking computer operating systems, a daemon is a computer program that runs as a background process, rather than being under the direct control of an interactive user...
in UNIX and servicesWindows ServiceOn Microsoft Windows operating systems, a Windows service is a long-running executable that performs specific functions and which is designed not to require user intervention. Windows services can be configured to start when the operating system is booted and run in the background as long as...
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 or take remedial measures themselves.
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.
Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
and Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
server operating systems are deployed on a minority of servers, as are other proprietary mainframe
Mainframe computer
Mainframes are powerful computers used primarily by corporate and governmental organizations for critical applications, bulk data processing such as census, industry and consumer statistics, enterprise resource planning, and financial transaction processing.The term originally referred to the...
operating systems, such as z/OS
Z/OS
z/OS is a 64-bit operating system for mainframe computers, produced by IBM. It derives from and is the successor to OS/390, which in turn followed a string of MVS versions.Starting with earliest:*OS/VS2 Release 2 through Release 3.8...
. The dominant operating systems among servers are UNIX-based or open source
Open source
The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...
kernel
Kernel (computing)
In computing, the kernel is the main component of most computer operating systems; it is a bridge between applications and the actual data processing done at the hardware level. The kernel's responsibilities include managing the system's resources...
distributions
Software distribution
Software distribution can refer to:* The process of software distribution, from creator to the user,* A collection of software, also referred to as a distribution, or a distro, which is set of software components built, assembled and configured so that it can be used essentially "as is" for its...
, such as Linux (the kernel)
Linux kernel
The Linux kernel is an operating system kernel used by the Linux family of Unix-like operating systems. It is one of the most prominent examples of free and open source software....
.
The rise of the microprocessor
Microprocessor
A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...
-based server was facilitated by the development of Unix to run on the x86 microprocessor architecture
Computer architecture
In computer science and engineering, computer architecture is the practical art of selecting and interconnecting hardware components to create computers that meet functional, performance and cost goals and the formal modelling of those systems....
. The Microsoft Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
family of operating systems also runs on x86 hardware and, since Windows NT
Windows NT
Windows NT is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. It was a powerful high-level-language-based, processor-independent, multiprocessing, multiuser operating system with features comparable to Unix. It was intended to complement...
, 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 application
Web application
A web application is an application that is accessed over a network such as the Internet or an intranet. The term may also mean a computer software application that is coded in a browser-supported language and reliant on a common web browser to render the application executable.Web applications are...
s and middleware
Middleware
Middleware is computer software that connects software components or people and their applications. The software consists of a set of services that allows multiple processes running on one or more machines to interact...
platforms has also lessened the demand for specialist application servers.
Types of servers
In a general network environment the following types of servers may be found.- Application serverApplication serverAn application server is a software framework that provides an environment in which applications can run, no matter what the applications are or what they do...
, a server dedicated to running certain software applications - Catalog serverCatalog serverA catalog server provides a single point of access that allows users to centrally search for information across a distributed network. In other words, it indexes databases, files and information across large network and allows keywords, Boolean and other searches...
, a central search point for information across a distributed network - Communications serverCommunications serverCommunications servers are open, standards-based computing systems that operate as a carrier-grade common platform for a wide range of communications applications and allow equipment providers to add value at many levels of the system architecture....
, carrier-grade computing platform for communications networks - Database serverDatabase serverA database server is a computer program that provides database services to other computer programs or computers, as defined by the client–server model. The term may also refer to a computer dedicated to running such a program...
, provides database services to other computer programs or computers - Fax serverFax serverA fax server is a system installed in a local area network server that allows computer users whose computers are attached to the LAN to send and receive fax messages...
, provides fax services for clients - File serverFile serverIn computing, a file server is a computer attached to a network that has the primary purpose of providing a location for shared disk access, i.e. shared storage of computer files that can be accessed by the workstations that are attached to the computer network...
, provides file services - Game serverGame serverA game server is a remotely or locally run server used by game clients to play multiplayer video games. Most video games played over the Internet operate via a connection to a game server...
, a server that video game clients connect to in order to play online together - Home serverHome serverA home server is a server located in a private residence providing services to other devices inside and/or outside the household through a home network and/or the Internet. Such services may include file and/or printer serving, media center serving, web serving, web caching, account authentication...
, a server for the home - Name serverName serverIn computing, a name server is a program or computer server that implements a name-service protocol. It maps a human-recognizable identifier to a system-internal, often numeric, identification or addressing component....
or DNS server - Print serverPrint serverA print server, or printer server, is a device that connects printers to client computers over a network. It can accept print jobs from the computers and send the jobs to the appropriate printers....
, provides printer services - Proxy serverProxy serverIn computer networks, a proxy server is a server that acts as an intermediary for requests from clients seeking resources from other servers. A client connects to the proxy server, requesting some service, such as a file, connection, web page, or other resource available from a different server...
, acts as an intermediary for requests from clients seeking resources from other servers - Sound serverSound serverA sound server is software that manages the use of and access to audio devices, most notably, the soundcard. It usually runs as a background process...
, provides multimedia broadcasting, streaming. - Standalone serverStandalone serverA Standalone server is a type of server that is not part of a larger network infrastructure such as an Active Directory domain. In a general sense, a standalone server provides services to clients without relying on any external resources, including authentication...
, an emulator for client–server (web-based) programs - Web serverWeb serverWeb server can refer to either the hardware or the software that helps to deliver content that can be accessed through the Internet....
, a server that HTTP clients connect to in order to send commands and receive responses along with data contents
Almost the entire structure of the Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
is based upon a client–server model. High-level root nameserver
Root nameserver
A root name server is a name server for the Domain Name System's root zone. It directly answers requests for records in the root zone and answers other requests returning a list of the designated authoritative name servers for the appropriate top-level domain...
s, DNS servers
Domain name system
The Domain Name System is a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities...
, and routers direct the traffic on the internet. There are millions of servers connected to the Internet, running continuously throughout the world.
- World Wide WebWorld Wide WebThe World Wide Web is a system of interlinked hypertext documents accessed via the Internet...
- Domain Name SystemDomain name systemThe Domain Name System is a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities...
- E-mailE-mailElectronic mail, commonly known as email or e-mail, is a method of exchanging digital messages from an author to one or more recipients. Modern email operates across the Internet or other computer networks. Some early email systems required that the author and the recipient both be online at the...
- FTP file transferFile Transfer ProtocolFile Transfer Protocol is a standard network protocol used to transfer files from one host to another host over a TCP-based network, such as the Internet. FTP is built on a client-server architecture and utilizes separate control and data connections between the client and server...
- ChatOnline chatOnline chat may refer to any kind of communication over the Internet, that offers an instantaneous transmission of text-based messages from sender to receiver, hence the delay for visual access to the sent message shall not hamper the flow of communications in any of the directions...
and instant messagingInstant messagingInstant Messaging is a form of real-time direct text-based chatting communication in push mode between two or more people using personal computers or other devices, along with shared clients. The user's text is conveyed over a network, such as the Internet... - Voice communication
- Streaming audio and videoStreaming mediaStreaming media is multimedia that is constantly received by and presented to an end-user while being delivered by a streaming provider.The term "presented" is used in this article in a general sense that includes audio or video playback. The name refers to the delivery method of the medium rather...
- Online gamingOnline gameAn online game is a game played over some form of computer network. This almost always means the Internet or equivalent technology, but games have always used whatever technology was current: modems before the Internet, and hard wired terminals before modems...
- Database serverDatabase serverA database server is a computer program that provides database services to other computer programs or computers, as defined by the client–server model. The term may also refer to a computer dedicated to running such a program...
s
Virtually every action taken by an ordinary Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
user requires one or more interactions with one or more servers.
There are also technologies that operate on an inter-server
Inter-server
In computer network protocol design, inter-server communication is an extension of the client–server model in which data are exchanged directly between servers...
level. Other services do not use dedicated servers; for example peer-to-peer file sharing
File sharing
File sharing is the practice of distributing or providing access to digitally stored information, such as computer programs, multimedia , documents, or electronic books. It may be implemented through a variety of ways...
, some implementations of telephony
Telephony
In telecommunications, telephony encompasses the general use of equipment to provide communication over distances, specifically by connecting telephones to each other....
(e.g. Skype
Skype
Skype is a software application that allows users to make voice and video calls and chat over the Internet. Calls to other users within the Skype service are free, while calls to both traditional landline telephones and mobile phones can be made for a fee using a debit-based user account system...
), and supplying television programs to several users (e.g. Kontiki
Kontiki
Kontiki is a peer-assisted content delivery technology company, founded in November 2000. It was acquired by VeriSign in March 2006. VeriSign, as part of a major divestiture, sold Kontiki to MK Capital in May 2008....
, SlingBox
Slingbox
The Slingbox is a TV streaming media device made by Sling Media that encodes video into the VC-1 format for transmission over the Internet and provides an infrared blaster. The video encoding and IR blaster can both be operated remotely over the Internet...
).
Energy consumption of servers
In 2010, servers were responsible for 2.5% of energy consumption in the United StatesUnited States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. A further 2.5% of United States energy consumption was used by cooling systems required to cool the servers. In 2010 it was estimated that by 2020 servers would use more of the world's energy than air travel if current trends continued.
Size classes
Sizes include:- Rack Server
- Tower Server
- Miniature (Home) Servers
- Mini Rack Servers
See also
Server definitions:- Home serverHome serverA home server is a server located in a private residence providing services to other devices inside and/or outside the household through a home network and/or the Internet. Such services may include file and/or printer serving, media center serving, web serving, web caching, account authentication...
- File serverFile serverIn computing, a file server is a computer attached to a network that has the primary purpose of providing a location for shared disk access, i.e. shared storage of computer files that can be accessed by the workstations that are attached to the computer network...
- Print serverPrint serverA print server, or printer server, is a device that connects printers to client computers over a network. It can accept print jobs from the computers and send the jobs to the appropriate printers....
- Media serverMedia ServerA media server refers either to a dedicated computer appliance or to a specialized application software, ranging from an enterprise class machine providing video on demand, to, more commonly, a small personal computer or NAS for the home, dedicated for storing various digital media .-Purpose:By...