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First located atCERNwith its original sticker that says: This machine is a server. DO NOT POWER IT DOWN!!
Incomputing, aserveris acomputer programor adevicethat provides functionality for other programs or devices, calledclients. Thisarchitectureis called theclientserver model, and a single overall computation is distributed across multiple processes or devices. Servers can provide various functionalities, often called services, such as sharing data orresourcesamong multiple clients, or performing computation for a client. A single server can serve multiple clients, and a single client can use multiple servers. A client process may run on the same device or may connect over a network to a server on a different device.Typical servers aredatabase serversfile serversmail serversprint serversweb serversgame servers, andapplication servers.
Clientserver systems are today most frequently implemented by (and often identified with) therequestresponsemodel: a client sends a request to the server, which performs some action and sends a response back to the client, typically with a result or acknowledgement. Designating a computer as server-class hardware implies that it is specialized for running servers on it. This often implies that it is more powerful and reliable than standardpersonal computers, but alternatively, largecomputing clustersmay be composed of many relatively simple, replaceable server components.
The use of the wordserverin computing comes fromqueueing theory,where it dates to the mid 20th century, being notably used inKendall (1953)(along with service), the paper that introducedKendalls notation. In earlier papers, such as theErlang (1909), more concrete terms such as [telephone] operators are used.
In computing, server dates at least toRFC 5(1969),one of the earliest documents describingARPANET(the predecessor ofInternet), and is contrasted with user, distinguishing two types ofhost: server-host and user-host. The use of serving also dates to early documents, such asRFC 4,contrasting serving-host with using-host.
TheJargon Filedefinesserverin the common sense of a process performing service for requests, usually remote, with the 1981 (1.1.0) version reading:
SERVER n. A kind ofDAEMONwhich performs a service for the requester, which often runs on a computer other than the one on which the server runs.
Strictly speaking, the termserverrefers to acomputer programorprocess(running program). Throughmetonymy, it refers to a device used for (or a device dedicated to) running one or several server programs. On a network, such a device is called ahost. In addition toserver, the wordsserveandservice(as noun and as verb) are frequently used, thoughservicerandservantare not.[a]The wordservice(noun) may refer to either the abstract form of functionality, e.g.Web service. Alternatively, it may refer to a computer program that turns a computer into a server, e.g.Windows service. Originally used as servers serve users (and users use servers), in the sense of obey, today one often says that servers serve data, in the same sense as give. For instance,web serversserve [up] web pages to users or service their requests.
The server is part of theclientserver model; in this model, a server serves data forclients. The nature of communication between a client and server isrequest and response. This is in contrast withpeer-to-peermodel in which the relationship is on-demand reciprocation. In principle, any computerized process that can be used or called by another process (particularly remotely, particularly to share a resource) is a server, and the calling process or processes is a client. Thus any general purpose computer connected to a network can host servers. For example, if files on a device are shared by some process, that process is afile server. Similarly,web serversoftware canrunon any capable computer, and so alaptopor a personal computer can host a web server.
While requestresponse is the most common clientserver design, there are others, such as thepublishsubscribe pattern. In the publishsubscribe pattern, clients register with a pubsub server, subscribing to specified types of messages; this initial registration may be done by requestresponse. Thereafter, the pubsub server forwards matching messages to the clientswithoutany further requests: the serverpushesmessages to the client, rather than the clientpullingmessages from the server as in requestresponse.
When referring to hardware, the wordservertypically designates computer models specialized for their role. In general, a server performs its role better than a genericpersonal computer.
The purpose of a server is to share data as well as to shareresourcesand distribute work. A server computer can serve its own computer programs as well; depending on the scenario, this could be part of aquid pro quotransaction, or simply a technical possibility. The following table shows several scenarios in which a server is used.
Hostsweb apps(computer programs that run inside aweb browser) allowing users in the network to run and use them, without having to install a copy on their own computers. Unlike what the name might imply, these servers need not be part of theworld wide web; anylocal networkwould do.
Maintains an index or table of contents of information that can be found across a large distributed network, such as computers, users, files shared on file servers, and web apps.Directory serversandname serversare examples of catalog servers.
Any computer program that needs to find something on the network, such aDomain memberattempting to log in, anemail clientlooking for an email address, or a user looking for a file
Maintains an environment needed for one communication endpoint (user or devices) to find other endpoints and communicate with them. It may or may not include a directory of communication endpoints and a presence detection service, depending on the openness and security parameters of the network
Communication endpoints (users or devices)
Shares vast amounts of computing resources, especiallyCPUandrandom-access memory, over a network.
Any computer program that needs more CPU power and RAM than a personal computer can probably afford. The client must be a networked computer; otherwise, there would be no clientserver model.
Maintains and shares any form ofdatabase(organized collections of data with predefined properties that may be displayed in a table) over a network.
Spreadsheetsaccounting softwareasset management softwareor virtually any computer program that consumes well-organized data, especially in large volumes
Shares one or morefax machinesover a network, thus eliminating the hassle of physical access
Sharesfilesandfolder, storage space to hold files and folders, or both, over a network
Networked computers are the intended clients, even though local programs can be clients
Enables several computers or gaming devices to playmultiplayer games
Personal computers orgaming consoles
Makesemailcommunication possible in the same way that apost officemakessnail mailcommunication possible
Sharesdigital videoordigital audioover a network throughmedia streaming(transmitting content in a way that portions received can be watched or listened as they arrive, as opposed downloading a whole huge file and then using it)
User-attended personal computers equipped with a monitor and a speaker
Shares one or moreprintersover a network, thus eliminating the hassle of physical access
Computers in need of printing something
Enables computer programs of a computer to play sound and record sound, individually or cooperatively
Computer programs of the same computer
Acts as anintermediarybetween a client and a server, accepting incoming traffic from the client and sending it to the server. Reasons for doing so includes content control and filtering, improving traffic performance, preventing unauthorized network access or simply routing the traffic over a large and complex network.
Hostsweb pages. A web server is what makesworld wide webpossible. Eachwebsitehas one or more web servers.
Almost the entire structure of theInternetis based upon aclientservermodel. High-levelroot nameserversDNS, and routers direct the traffic on the internet. There are millions of servers connected to the Internet, running continuously throughout the worldand virtually every action taken by an ordinaryInternetuser requires one or more interactions with one or more server. There are exceptions that do not use dedicated servers; for examplepeer-to-peer file sharing, some implementations oftelephony(e.g. pre-MicrosoftSkype).
Hardwarerequirement for servers vary widely, depending on the servers purpose and its software.
Since servers are usually accessed over a network, many run unattended without acomputer monitoror input device, audio hardware andUSBinterfaces. Many servers do not have agraphical user interface(GUI). They are configured and managed remotely. Remote management can be conducted via various methods includingMicrosoft Management Console(MMC),PowerShellSSHandsystems such as DellsiDRACor HPsiLo.
Large traditional single servers would need to be run for long periods without interruption.Availabilitywould have to be very high, making hardware reliability and durability extremely important.Mission-criticalenterprise servers would be veryfault tolerantand use specialized hardware with lowfailure ratesin order to maximizeuptimeUninterruptible power suppliesmight be incorporated to insure against power failure. Servers typically include hardwareredundancysuch as dualpower suppliessystems, andECC memory,along with extensivepre-bootmemory testing and verification. Critical components might behot swappable, allowing technicians to replace them on the running server without shutting it down, and to guard against overheating, servers might have more powerful fans or usewater cooling. They will often be able to be configured, powered up and down or rebooted remotely, usingout-of-band management, typically based onIPMI. Server casings are usuallyflat and wide, and designed to berack-mounted.
These types of servers are often housed in dedicateddata centers. These will normally have very stable power and Internet and increased security. Noise is also less of a concern, but power consumption and heat output can be a serious issue. Server rooms are equipped with air conditioning devices.
Aserver rackseen from the rear
Wikimedia Foundationservers as seen from the front
Wikimedia Foundationservers as seen from the rear
Wikimedia Foundationservers as seen from the rear
Aserver farmorserver clusteris a collection of computer servers maintained by an organization to supply server functionality far beyond the capability of a single device. Moderndata centersare now often built of very large clusters of much simpler servers,and there is a collaborative effort,Open Compute Projectaround this concept.
A class of small specialist servers callednetwork appliancesare generally at the low end of the scale, often being smaller than common desktop computers.
SunsCobalt Qube3; a computerserver appliance(2002); running Cobalt Linux (a customized version of Red Hat Linux, using the 2.2 Linux kernel), complete with the Apache web server.
On the Internet the dominant operating systems among servers are UNIX-like, such as those based onLinuxandFreeBSD,withWindows Serveralso having a very significant share. Proprietary operating systems such asz/OSandmacOS Serverare also deployed, but in much smaller numbers.
Specialist server-oriented operating systems have traditionally had features such as:
Ability toreconfigureand update both hardware and software to some extent without restart
Advancedbackupfacilities to permit regular and frequent online backups of criticaldata,
Transparentdata transfer between differentvolumesor devices
Flexible and advanced networking capabilities
Automation capabilities such asdaemonsin UNIX andservicesin Windows
Tight system security, with advanced user, resource, data, and memory protection.
Advanced detection and alerting on conditions such as overheating, processor and disk failure.
In practice, today many desktop and server operating systems share similarcode bases, differing mostly in configuration.
In 2010, data centers (servers, cooling, and other electrical infrastructure) were responsible for 1.1-1.5% of electrical energy consumption worldwide and 1.7-2.2% in the United States.One estimate is that total energy consumption for information and communications technology saves more than 5 times itscarbon footprintin the rest of the economy by enabling efficiency.
ACORBA servantis a server-sideobjectto whichmethod callsfromremote method invocationareforwarded, but this is an uncommon usage.
Windows Server Administration Fundamentals
. Microsoft Official Academic Course. 111 River Street, Hoboken, NJ 07030:John Wiley & Sons. 2011. pp.23.ISBN978-0-470-90182-3.
Comer, Douglas E.; Stevens, David L. (1993).
Vol III: Client-Server Programming and Applications
. Internetworking with TCP/IP. Department of Computer Sciences, Purdue University, West Lafayette, IN 479:Prentice Hall. pp.11d.ISBN0-13-474222-2.
Richard A. Henle, Boris W. Kuvshinoff, C. M. Kuvshinoff (1992).
. Oxford University Press. p.417.
Server is a fairly recent computer networking term derived from queuing theory.
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Using the HTTP Publish-Subscribe Server, Oracle
A Realistic Evaluation of Memory Hardware Errors and Software System Susceptibility. Usenix Annual Tech Conference 2010
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Google uncloaks once-secret server.
Usage statistics and market share of Linux for websites
Markoff, John (31 Jul 2011).Data Centers Using Less Power Than Forecast, Report Says.
SMART 2020: Enabling the low carbon economy in the information age
. 6 Oct 2008. Archived fromthe original
Wikimedia Commons has media related to
Erlang, Agner Krarup(1909).The theory of probabilities and telephone conversations
Kendall, D. G.(1953).Stochastic Processes Occurring in the Theory of Queues and their Analysis by the Method of the Imbedded Markov Chain.
The Annals of Mathematical Statistics
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This page was last edited on 9 December 2017, at 05:54.