Server (computing): Difference between revisions

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{{Short description|Computer to access a central resource or service on a network}}

[[File:Client-server-model.svg|thumb|right|200px|A [[computer network diagram]] of [[Client (computing)|client]] computers communicating with a server computer via the [[Internet]]]]

[[File:Wikimedia Foundation Servers-8055 35.jpg|thumb|[[Wikimedia Foundation]] rackmount servers on racks in a data center]]

[[File:First-server-cern-computer-center.jpg|thumb|The first [[World Wide Web|WWW]] server is located at [[CERN]] with its original sticker that says: "This machine is a server. DO NOT POWER IT DOWN!!"]]

A '''server''' is a [[computer]] that provides information to other computers called "[[Client (computing)|clients]]" on a [[computer network]].<ref name="Cisco Networking Academy x508">{{cite web | title=1.1.2.2 Clients and Servers | website=Cisco Networking Academy | url=http://cisco.num.edu.mn/CCNA_R&S1/course/module1/1.1.2.2/1.1.2.2.html | archive-url=https://web.archive.org/web/20240407111300/http://cisco.num.edu.mn/CCNA_R&S1/course/module1/1.1.2.2/1.1.2.2.html | quote=Servers are hosts that have software installed that enable them to provide information...Clients are computer hosts that have software installed that enable them to request and display the information obtained from the server. | access-date=2024-04-07| archive-date=2024-04-07 }}</ref> This [[Systems architecture|architecture]] is called the [[client–server model]]. Servers can provide various functionalities, often called "services", such as sharing data or [[System resource|resources]] among multiple clients or performing computations[[computation]]s 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.<ref>{{cite book |title = Windows Server Administration Fundamentals |url = https://archive.org/details/windowsserveradm00cour |url-access = limited |publisher = [[John Wiley & Sons]] |___location = Hoboken, NJ |series = Microsoft Official Academic Course |year = 2011 |pages = [https://archive.org/details/windowsserveradm00cour/page/n21 2]–3 |isbn = 978-0-470-90182-3}}</ref> Typical servers are [[database serversserver]]s, [[file serversserver]]s, [[mail serversserver]]s, [[print serversserver]]s, [[web serversserver]]s, [[game serversserver]]s, and [[application serversserver]]s.<ref>{{cite book|last1 = Comer |first1 = Douglas E. |last2 = Stevens |first2 = David L |title = Vol III: Client-Server Programming and Applications |publisher = [[Prentice Hall]] |___location = West Lafayette, IN |series = Internetworking with TCP/IP |year = 1993 |pages = 11d |isbn = 978-0-13-474222-9 |url-access = registration |url = https://archive.org/details/internetworkingw00come_0}}</ref>

Client–server systems are usually most frequently implemented by (and often identified with) the [[request–response]] model: 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 acknowledgment. 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 standard [[personal computerscomputer]]s, but alternatively, large [[computing clusterscluster]]s may be composed of many relatively simple, replaceable server components.

== History ==

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In computing, "server" dates at least to RFC 5 (1969),<ref name="rulifson">{{cite IETF |title=DEL |rfc=5 |last=Rulifson |first=Jeff |author-link=Jeff Rulifson |date=June 1969 |publisher=[[Internet Engineering Task Force|IETF]] |access-date=30 November 2013}}</ref> one of the earliest documents describing [[ARPANET]] (the predecessor of [[Internet]]), and is contrasted with "user", distinguishing two types of [[Host (network)|host]]: "server-host" and "user-host". The use of "serving" also dates to early documents, such as RFC 4,<ref>{{cite IETF |title=Network Timetable |rfc=4 |last=Shapiro |first=Elmer B. |date=March 1969 |publisher=[[Internet Engineering Task Force|IETF]] |access-date=30 November 2013}}</ref> contrasting "serving-host" with "using-host".

The [[Jargon File]] defines ''server'' in the common sense of a process performing service for requests, usually remote,<ref>[http://www.catb.org/jargon/html/S/server.html server]</ref> with the 1981 version reading:<ref>[{{Cite web| title=JARGON.TXT recovered from Fall 1981 RSX-11 SIG tape by Tim Shoppa | url=http://www.catb.org/jargon/oldversions/jarg110.txt] | archive-url=https://web.archive.org/web/20041021195648/http://www.catb.org:80/jargon/oldversions/jarg110.txt | archive-date=2004-10-21}}</ref>

{{quote |SERVER n. A kind of [[Daemon (computing)|DAEMON]] which performs a service for the requester, which often runs on a computer other than the one on which the server runs.}} The average utilization of a server in the early 2000s was 5 to 15%, but with the adoption of virtualization this figure started to increase to reduce the number of servers needed.<ref>{{cite web | url=https://semiengineering.com/chip-aging-accelerates/ | title=Chip Aging Accelerates | date=14 February 2018 }}</ref>

== Operation ==

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Strictly speaking, the term ''server'' refers to a [[computer program]] or [[process (computing)|process]] (running program). Through [[metonymy]], 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 a ''[[Host (network)|host]]''. In addition to ''server'', the words ''serve'' and ''service'' (as verb and as noun respectively) are frequently used, though ''servicer'' and ''servant'' are not.{{efn|A [[servant (CORBA)|CORBA servant]] is a server-side [[Object (computer science)|object]] to which [[method call]]s from [[remote method invocation]] are [[Forwarding (object-oriented programming)|forwarded]], but this is an uncommon usage.}} The word ''service'' (noun) may refer to 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 server]]s "serve [up] web pages to users" or "service their requests".

The server is part of the [[client–server model]]; in this model, a server serves data for [[Client (computing)|clients]]. The nature of communication between a client and server is [[Request–response|request and response]]. This is in contrast with [[peer-to-peer]] model 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 [[File system|files]] on a device are shared by some process, that process is a [[file server]]. Similarly, [[web server]] software can ''run'' on any capable computer, and so a [[laptop]] or a personal computer can host a web server.

While request–response is the most common client-server design, there are others, such as the [[publish–subscribe pattern]]. In the publish-subscribe pattern, clients register with a pub-sub server, subscribing to specified types of messages; this initial registration may be done by request-response. Thereafter, the pub-sub server forwards matching messages to the clients ''without'' any further requests: the server ''[[Push technology|pushes]]'' messages to the client, rather than the client ''[[Pull technology|pulling]]'' messages from the server as in request-response.<ref>[https://docs.oracle.com/cd/E24329_01/web.1211/e21049/pubsub.htm Using the HTTP Publish-Subscribe Server], Oracle</ref>

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|[[Catalog server]]

|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 server]]s and [[name server]]s are examples of catalog servers.

|Any computer program that needs to find something on the network, such as a [[Windows ___domain|Domain member]] attempting to log in, an [[email client]] looking for an email address, or a user looking for a file

|-

|[[Communications server]]

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=== Large servers ===

Large traditional single servers would need to be run for long periods without interruption. [[Availability]] would have to be very high, making hardware reliability and durability extremely important. [[Mission-critical]] enterprise servers would be very [[Fault tolerance|fault tolerant]] and use specialized hardware with low [[failure ratesrate]]s in order to maximize [[uptime]]. [[Uninterruptible power supply|Uninterruptible power supplies]] might be incorporated to guard against power failure. Servers typically include hardware [[Redundancy (engineering)|redundancy]] such as dual [[power supply|power supplies]], [[RAID]] [[hard disk|disk]] systems, and [[ECC memory]],<ref>{{cite web|url=http://www.cs.rochester.edu/~kshen/papers/usenix2010-li.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.cs.rochester.edu/~kshen/papers/usenix2010-li.pdf |archive-date=2022-10-09 |url-status=live|title="A Realistic Evaluation of Memory Hardware Errors and Software System Susceptibility". Usenix Annual Tech Conference 2010|author=Li|author2=Huang|author3=Shen|author4=Chu|year=2010|access-date=2017-01-30}}</ref> along with extensive [[Preboot Execution Environment|pre-boot]] memory testing and verification. Critical components might be [[hot 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 use [[water cooling]]. They will often be able to be configured, powered up and down, or rebooted remotely, using [[out-of-band management]], typically based on [[Intelligent Platform Management Interface|IPMI]]. Server casings are usually [[rack unit|flat and wide]], and designed to be rack-mounted, either on [[19-inch racksrack]]s or on [[Open RacksRack]]s.

These types of servers are often housed in dedicated [[data 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.

{{gallery

|File:DL380sREAR.jpg|A [[server rack]] seen from the rear

|File:Wikimedia Foundation Servers-8055 08.jpg|[[Wikimedia Foundation]] servers as seen from the front

|File:Wikimedia Foundation Servers-8055 23.jpg|[[Wikimedia Foundation]] servers as seen from the rear

|File:Wikimedia Foundation Servers-8055 02.jpg|[[Wikimedia Foundation]] servers as seen from the rear

}}

=== Clusters ===

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* Automation capabilities such as [[Daemon (computer software)|daemons]] in UNIX and [[Windows service|services]] in 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.<ref>{{cite web|title=Server Oriented Operating System|url=http://www.ingelec.uns.edu.ar/rts/soos/|access-date=2010-05-25|archive-url=http://web.archive.org/web/20110531174040/http://www.ingelec.uns.edu.ar/rts/soos/|archive-date=31 May 2011}}</ref>

In practice, today many desktop and server operating systems share similar [[code base]]s, differing mostly in configuration.

== Energy consumption ==

In 20102024, data centers (servers, cooling, and other electrical infrastructure) consumed 415 [[Kilowatt-hour|terawatt-hours]] of electrical energy, and were responsible for roughly 1.1–1.5% of electrical energy consumption worldwide,<ref>{{Cite andweb 1.7–2.2%|last=magazine in|first=Sophia theChen, UnitedNature States.<ref>{{cite|title=Data Centers Will Use Twice as Much Energy by 2030—Driven by newsAI |url=https://www.nytimesscientificamerican.com/2011/08/01/technologyarticle/ai-will-drive-doubling-of-data-centerscenter-usingenergy-lessdemand-powerby-than2030/ |access-forecastdate=2025-report06-says.html?_r17 |website=0Scientific American |titlelanguage=Dataen}}</ref> Centersand Usingfor Less4.4% Powerin Thanthe Forecast,United ReportStates.<ref>{{Cite Saysreport |dateurl=31https://escholarship.org/uc/item/32d6m0d1 Jul|title=2024 2011United States Data Center Energy Usage Report |newspaperlast=[[NYHamm Times]]|first=Geoff |access-date=18 Jan 20132025 |firstpublisher=JohnLawrence Berkely National Laboratory |lastdoi=Markoff10.71468/p1wc7q}}</ref>{{Update inline|date=November 2023}} One estimate is that total energy consumption for information and communications technology saves more than 5 times its [[carbon footprint]]<ref>{{cite web |url=http://www.smart2020.org/_assets/files/02_Smart2020Report.pdf |archive-url=https://web.archive.org/web/20101122051650/http://www.smart2020.org/_assets/files/02_Smart2020Report.pdf |archive-date=22 November 2010 |title=SMART 2020: Enabling the low carbon economy in the information age |date=6 Oct 2008 |publisher=[[The Climate Group]] |access-date=18 Jan 2013 }}</ref> in the rest of the economy by increasing efficiency.

Global energy consumption is increasing due to the increasing demand of data and bandwidth. [[Natural Resources Defense Council]] (NRDC) states that data centers used 91 billion kilowatt hours (kWh) electrical energy in 2013 which accounts to 3% of global electricity usage.<ref>https://lifelinedatacenters.com/data-center/reduce-data-center-carbon-footprints/</ref>{{Update inline|date=November 2023}}

[[Environmental groups]] have placed focus on the carbon emissions of data centers as it accounts to 200 million metric tons of [[carbon dioxide]] in a year.