Server (computing)

In computing, a server is a computer program or a device that provides functionality for other programs or devices, called "clients". This architecture is called the client–server 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 or resources among 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.[1] Typical servers are database servers, file servers, mail servers, print servers, web servers, game servers, and application servers.[2]

Client–server systems are today 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 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 standard personal computers, but alternatively, large computing clusters may be composed of many relatively simple, replaceable server components.

First WWW server located at CERN with its original sticker that says: "This machine is a server. DO NOT POWER IT DOWN!!"


The use of the word server in computing comes from queueing theory,[3] where it dates to the mid 20th century, being notably used in Kendall (1953) (along with "service"), the paper that introduced Kendall's notation. In earlier papers, such as the Erlang (1909), more concrete terms such as "[telephone] operators" are used.

In computing, "server" dates at least to RFC 5 (1969),[4] one of the earliest documents describing ARPANET (the predecessor of Internet), and is contrasted with "user", distinguishing two types of host: "server-host" and "user-host". The use of "serving" also dates to early documents, such as RFC 4,[5] contrasting "serving-host" with "using-host".

The Jargon File defines "server" in the common sense of a process performing service for requests, usually remote, with the 1981 (1.1.0) version reading:

SERVER n. A kind of DAEMON which performs a service for the requester, which often runs on a computer other than the one on which the server runs.


A network based on the client–server model where multiple individual clients request services and resources from centralized servers

Strictly speaking, the term server refers to a computer program or 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. In addition to server, the words serve and service (as noun and as verb) are frequently used, though servicer and servant are not.[a] The word service (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 servers "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 clients. The nature of communication between a client and server is 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 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 pushes messages to the client, rather than the client pulling messages from the server as in request–response.[6]


The purpose of a server is to share data as well as to share resources and distribute work. A server computer can serve its own computer programs as well; depending on the scenario, this could be part of a quid pro quo transaction, or simply a technical possibility. The following table shows several scenarios in which a server is used.

Server type Purpose Clients
Application server Hosts web apps (computer programs that run inside a web 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 the World Wide Web; any local network would do. Computers with a web browser
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 servers and name servers are examples of catalog servers. Any computer program that needs to find something on the network, such a Domain member attempting to log in, an email client looking for an email address, or a user looking for a file
Communications server 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)
Computing server Shares vast amounts of computing resources, especially CPU and random-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 client–server model.
Database server Maintains and shares any form of database (organized collections of data with predefined properties that may be displayed in a table) over a network. Spreadsheets, accounting software, asset management software or virtually any computer program that consumes well-organized data, especially in large volumes
Fax server Shares one or more fax machines over a network, thus eliminating the hassle of physical access Any fax sender or recipient
File server Shares files and folders, 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
Game server Enables several computers or gaming devices to play multiplayer video games Personal computers or gaming consoles
Mail server Makes email communication possible in the same way that a post office makes snail mail communication possible Senders and recipients of email
Media server Shares digital video or digital audio over a network through media streaming (transmitting content in a way that portions received can be watched or listened to as they arrive, as opposed to downloading an entire file and then using it) User-attended personal computers equipped with a monitor and a speaker
Print server Shares one or more printers over a network, thus eliminating the hassle of physical access Computers in need of printing something
Sound server Enables computer programs to play and record sound, individually or cooperatively Computer programs of the same computer and network clients.
Proxy server Acts as an intermediary between 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. Any networked computer
Virtual server Shares hardware and software resources with other virtual servers. It exists only as defined within specialized software called hypervisor. The hypervisor presents virtual hardware to the server as if it were real physical hardware.[7] Server virtualization allows for a more efficient infrastructure. Any networked computer
Web server Hosts web pages. A web server is what makes the World Wide Web possible. Each website has one or more web servers. Computers with a web browser

Almost the entire structure of the Internet is based upon a client–server model. High-level root nameservers, DNS, and routers direct the traffic on the internet. There are millions of servers connected to the Internet, running continuously throughout the world[8] and virtually every action taken by an ordinary Internet user requires one or more interactions with one or more server. There are exceptions that do not use dedicated servers; for example peer-to-peer file sharing, some implementations of telephony (e.g. pre-Microsoft Skype).


Inside and Rear of Webserver
A rack-mountable server with the top cover removed to reveal internal components

Hardware requirement for servers vary widely, depending on the server's purpose and its software.

Since servers are usually accessed over a network, many run unattended without a computer monitor or input device, audio hardware and USB interfaces. Many servers do not have a graphical user interface (GUI). They are configured and managed remotely. Remote management can be conducted via various methods including Microsoft Management Console (MMC), PowerShell, SSH and browser-based out-of-band management systems such as Dell's iDRAC or HP's iLo.

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 tolerant and use specialized hardware with low failure rates in order to maximize uptime. Uninterruptible power supplies might be incorporated to guard against power failure. Servers typically include hardware redundancy such as dual power supplies, RAID disk systems, and ECC memory,[9] along with extensive 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 IPMI. Server casings are usually flat and wide, and designed to be rack-mounted.

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.


A server rack seen from the rear

Wikimedia Foundation Servers-8055 08

Wikimedia Foundation servers as seen from the front

Wikimedia Foundation Servers-8055 23

Wikimedia Foundation servers as seen from the rear

Wikimedia Foundation Servers-8055 02

Wikimedia Foundation servers as seen from the rear


A server farm or server cluster is a collection of computer servers maintained by an organization to supply server functionality far beyond the capability of a single device. Modern data centers are now often built of very large clusters of much simpler servers,[10] and there is a collaborative effort, Open Compute Project around this concept.


A class of small specialist servers called network appliances are generally at the low end of the scale, often being smaller than common desktop computers.

Operating systems

Cobalt Qube 3 Front
Sun's Cobalt Qube 3; a computer server 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 open-source distributions, such as those based on Linux and FreeBSD,[11] with Windows Server also having a very significant share. Proprietary operating systems such as z/OS and macOS Server are also deployed, but in much smaller numbers.

Specialist server-oriented operating systems have traditionally had features 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
  • Tight system security, with advanced user, resource, data, and memory protection.
  • Advanced detection and alerting on conditions such as overheating, processor and disk failure.[12]

In practice, today many desktop and server operating systems share similar code bases, differing mostly in configuration.

Energy consumption

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.[13] One estimate is that total energy consumption for information and communications technology saves more than 5 times its carbon footprint[14] in the rest of the economy by increasing efficiency.

See also


  1. ^ A CORBA servant is a server-side object to which method calls from remote method invocation are forwarded, but this is an uncommon usage.


  1. ^ Windows Server Administration Fundamentals. Microsoft Official Academic Course. 111 River Street, Hoboken, NJ 07030: John Wiley & Sons. 2011. pp. 2–3. ISBN 978-0-470-90182-3.
  2. ^ 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. ISBN 978-0-13-474222-9.
  3. ^ Richard A. Henle, Boris W. Kuvshinoff, C. M. Kuvshinoff (1992). Desktop computers: in perspective. Oxford University Press. p. 417. Server is a fairly recent computer networking term derived from queuing theory.CS1 maint: Uses authors parameter (link)
  4. ^ Rulifson, Jeff (June 1969). DEL. IETF. doi:10.17487/RFC0005. RFC 5. Retrieved 30 November 2013.
  5. ^ Shapiro, Elmer B. (March 1969). Network Timetable. IETF. doi:10.17487/RFC0004. RFC 4. Retrieved 30 November 2013.
  6. ^ Using the HTTP Publish-Subscribe Server, Oracle
  7. ^ IT Explained. "Server - Definition and Details".
  8. ^ "Web Servers". IT Business Edge. Retrieved July 31, 2013.
  9. ^ Li, Huang, Shen, Chu (2010). ""A Realistic Evaluation of Memory Hardware Errors and Software System Susceptibility". Usenix Annual Tech Conference 2010" (PDF). Retrieved 2017-01-30.CS1 maint: Multiple names: authors list (link)
  10. ^ "Google uncloaks once-secret server". CNET. CBS Interactive. Retrieved 2017-01-30.
  11. ^ "Usage statistics and market share of Linux for websites". Retrieved 18 Jan 2013.
  12. ^ "Server Oriented Operating System". Retrieved 2010-05-25.
  13. ^ Markoff, John (31 Jul 2011). "Data Centers Using Less Power Than Forecast, Report Says". NY Times. Retrieved 18 Jan 2013.
  14. ^ "SMART 2020: Enabling the low carbon economy in the information age" (PDF). The Climate Group. 6 Oct 2008. Archived from the original (PDF) on 22 November 2010. Retrieved 18 Jan 2013.

Further reading

Alain Lefebvre

Alain Lefebvre (born 1960) is a French entrepreneur, now Author of several books.

He is recognized as a French pioneer in the client server computing and Internet era. Cofounder of SQLI in 1990, with a successful IPO in the summer of 2000 during the Internet bubble burst. He led the company for over ten years, and also was recognized for his columns and essays on the computing market in France during this 15 years period. Alain Lefebvre has published more than 20 books including four on the Computer and Internet topics. Since 1995, he is involved with his wife, Murielle Lefebvre to promote the Montessori education and business in France. Alain Lefebvre is the founder of the first professional social network in France, Precursor and Visionary in France of the web 2.0 movement he spoke to network events, conferences and interviews as a French pioneer in 2004. He also published a book about the social networks in 2005.

Application server

An application server is a software framework that provides both facilities to create web applications and a server environment to run them.Application Server Frameworks contain a comprehensive service layer model. An application server acts as a set of components accessible to the software developer through a standard API defined for the platform itself. For Web applications, these components are usually performed in the same running environment as their web server(s), and their main job is to support the construction of dynamic pages. However, many application servers target much more than just Web page generation: they implement services like clustering, fail-over, and load-balancing, so developers can focus on implementing the business logic.In the case of Java application servers, the server behaves like an extended virtual machine for running applications, transparently handling connections to the database on one side, and, often, connections to the Web client on the other.Other uses of the term may refer to the services that a server makes available or the computer hardware on which the services run.


Things known as BIND or Bind include:

BIND, Berkeley Internet Name Domain, a DNS server

Bookbinding, the process of physically assembling a book from a number of folded or unfolded sheets of paper or other material

Foot binding, the custom of applying painfully tight binding to the feet of young girls to prevent further growth

bind is an operation of monads in functional programming

bind a client to a server in client–server computing

Bind caste, Indian caste name

Bind rune, a ligature of two or more runes

Bind (chess), a strong grip or stranglehold on a position that is difficult for the opponent to break

Bind (higher-order function), an operation in a monad

Client–server model

Client–server model is a distributed application structure that partitions tasks or workloads between the providers of a resource or service, called servers, and service requesters, called clients. Often clients and servers communicate over a computer network on separate hardware, but both client and server may reside in the same system. A server host runs one or more server programs which share their resources with clients. A client does not share any of its resources, but requests a server's content or service function. Clients therefore initiate communication sessions with servers which await incoming requests.

Examples of computer applications that use the client–server model are Email, network printing, and the World Wide Web.


DC/OSx (DataCenter/OSx) is a discontinued Unix operating system for MIPS based systems developed by Pyramid Technology. It ran on its Nile series of SMP machines and was a port of AT&T System V Release 4 (SVR4). In 1995, Pyramid Technology was acquired by Siemens Nixdorf Informationssysteme (SNI), and DC/OSx was superseded by the SINIX operating system.

Distributed networking

Distributed networking is a distributed computing network system where components of the program and data depend on multiple sources.

Dynamic provisioning environment

Dynamic provisioning environment (DPE) is a simplified way to explain a complex networked server computing environment where server computing instances or virtual machines (VMs) are provisioned (deployed or instantiated) from a centralized administrative console or client application by the server administrator, network administrator, or any other enabled user. The server administrator or network administrator has the ability to parse out control of the provisioning environment to users or accounts in the network environment (end users, organizational units, network accounts, other administrators). The provisioned servers or VMs can be inside the firewall, outside the firewall, or hosted depending on how the supporting pool of networked server computing resources is defined. From the perspective of the end user/client the requested server is deployed automatically.

From a simple to use client application / desktop application any administrator or designated end user is able to easily instantiate a server instance or virtual machine(VM) instance. The server instance is provisioned for the eligible administrator or end user without anyone having to physically touch the supporting server infrastructure. While defining the server or VM to instantiate the client application gives the end user or administrator the ability to define the operating system and applications that will run within the server instance to be provisioned automatically.

Desktop dynamic provisioning environment (desktop DPE) or client dynamic provisioning environment (client DPE) is the scenario where a dynamic provisioning environment (DPE) is being used to provision client computing instances or desktop computing instances.

Origin of DPE (dynamic provisioning environment): First documented in 2007; Cambridge, Massachusetts US. "DPE" is the acronym for dynamic provisioning environment

DPE can be a vendor independent environment or an environment defined by a specific vendor. A dynamic provisioning environment (DPE) is flexible and can be defined as supporting a set of heterogeneous applications, defined as supporting a single application, or could be created in an appliance model to deploy a discrete application customized for a specific usage scenario.

From an operating system perspective a DPE server infrastructure can exist on one server operating system (homogeneous server infrastructure) or exist as on a defined set of servers with different multiple operating systems (heterogeneous server infrastructure). The server instances or VMs provisioned by the DPE could be one specific server operating system or multiple server operating systems. Same idea for client systems instantiated by the DPE. The client instantiated by the DPE could be one or multiple client/desktop operating systems.Components of a DPE will vary based on the density of the computing environment. Would commonly include, servers or virtual server instances, directory server, network connectivity( TCP/IP), management layer, virtual machine management tools, server provisioning tools, client application, client interface.

Enterprise system

Enterprise systems (ES) are large-scale application software packages that support business processes, information flows, reporting, and data analytics in complex organizations. While ES are generally packaged enterprise application software (PEAS) systems they can also be bespoke, custom developed systems created to support a specific organization's needs.

Types of enterprise systems include:

enterprise resources planning (ERP) systems,

enterprise planning systems, and

customer relationship management software.Although data warehousing or business intelligence systems are enterprise-wide packaged application software often sold by ES vendors, since they do not directly support execution of business processes, they are often excluded from the term.

Enterprise systems are built on software platforms, such as SAP’s NetWeaver and Oracle's Fusion, and databases.

From a hardware perspective, enterprise systems are the servers, storage and associated software that large businesses use as the foundation for their IT infrastructure. These systems are designed to manage large volumes of critical data. These systems are typically designed to provide high levels of transaction performance and data security.


The Gurobi Optimizer is a commercial optimization solver for linear programming (LP), quadratic programming (QP), quadratically constrained programming (QCP), mixed integer linear programming (MILP), mixed-integer quadratic programming (MIQP), and mixed-integer quadratically constrained programming (MIQCP).

Gurobi is named for its founders: Zonghao Gu, Edward Rothberg and Robert Bixby. Bixby was also the founder of CPLEX, while Rothberg and Gu led the CPLEX development team for nearly a decade.

IBM Balanced Configuration Unit

The IBM Data Warehousing Balanced Configuration Unit is a family of data warehousing server (computing)s from IBM. IBM introduced the Balanced Configuration Unit (BCU) for AIX in 2005, and the BCU for Linux in 2006. The BCU is a "balanced" combination of computer server hardware (cpus, I/O channels, and storage) combined with DB2 Data Warehouse Edition (DB2 DWE) software to form a data warehouse "appliance like" system to compete with systems such as Greenplum, DATAllegro, Netezza Performance Server, and Teradata.

See also IBM Linux Solution Optimizes Enterprise Data Warehousing.


JSON-RPC is a remote procedure call protocol encoded in JSON. It is a very simple protocol (and very similar to XML-RPC), defining only a few data types and commands. JSON-RPC allows for notifications (data sent to the server that does not require a response) and for multiple calls to be sent to the server which may be answered out of order.

Lotus Software

Lotus Software (called Lotus Development Corporation before its acquisition by IBM) was an American software company based in Massachusetts; it was "offloaded" to India's HCL Corporation in 2018.

Lotus is most commonly known for the Lotus 1-2-3 spreadsheet application, the first feature-heavy, user-friendly, reliable and WYSIWYG-enabled product to become widely available in the early days of the IBM PC, when there was no graphical user interface. Much later, in conjunction with Ray Ozzie's Iris Associates, Lotus also released a groupware and email system, Lotus Notes. IBM purchased the company in 1995 for US$3.5 billion, primarily to acquire Lotus Notes and to establish a presence in the increasingly important client–server computing segment, which was rapidly making host-based products such as IBM's OfficeVision obsolete..

On December 6, 2018, IBM announced the selling of Lotus Software/Domino to HCL for $1.8 billion dollars.


Middleware is computer software that provides services to software applications beyond those available from the operating system. It can be described as "software glue".Middleware makes it easier for software developers to implement communication and input/output, so they can focus on the specific purpose of their application. It gained popularity in the 1980s as a solution to the problem of how to link newer applications to older legacy systems, although the term had been in use since 1968.

Open Environment Corporation

Open Environment Corporation (OEC) was founded by John J. Donovan in 1992 in Cambridge, Massachusetts, USA. OEC develops, markets and supports software that enables companies to create applications for distributed, client/server computing systems. OEC pioneered a three-tiered software architecture that allows customer to rapidly develop, deploy and manage software applications to access critical information quickly on an enterprise-wide basis.OEC was bought out by Borland in 1996.

Robert Frankenberg

Robert J. Frankenberg (born 1947) is an American computer engineer and business executive who served as chairman, president and chief executive officer of Novell, Inc. from 1994 to 1996.


WaveMaker is a private aPaaS (application platform-as-a-service) software for building and running custom apps. WaveMaker provides Rapid API App Development & Deployment to build enterprise-grade multi-device apps, and leverages Docker containerization for an app-optimized infrastructure.


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