Server (computing): Difference between revisions

Revision as of 08:21, 17 February 2025

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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 ==

The use of the word ''server'' in computing comes from [[queueing theory]],<ref>{{cite book |title=Desktop computers: in perspective |author=Richard A. Henle |author2=Boris W. Kuvshinoff |author3=C. M. Kuvshinoff |publisher=Oxford University Press |year=1992 |url=https://books.google.com/books?id=g4krAAAAYAAJ&q=server+%22queuing+theory%22 |page=417 |isbn=978-0-19-507031-6 |quote=Server is a fairly recent computer networking term derived from queuing theory.}}</ref> where it dates to the mid 20th century, being notably used in {{Harvtxt|Kendall|1953}} (along with "service"), the paper that introduced [[Kendall's notation]]. In earlier papers, such as the {{Harvtxt|Erlang|1909}}, more concrete terms such as "[telephone] operators" are used.

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>[http://www.catb.org/jargon/oldversions/jarg110.txt]</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>

The average utilisation of a server in the early 2000s was 5 to 15%, but with the adoption of this figure started to increase to reduce the number of servers needed.

== Operation ==

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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, Huang, Shen, 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

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.

|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 ===