A server is a running instance of an application (software) capable of accepting requests from the client and giving responses accordingly. Servers can run on any computer including dedicated computers, which individually are also often referred to as the server. In many cases, a computer can provide several services and have several servers running. The advantage of running servers on a dedicated computer is security. For this reason most of the servers are daemon processes and designed in that they can be run on specific computer(s).Servers operate within a client-server architecture. Servers are computer programs running to serve the requests of other programs, the clients. Thus, the server performs some tasks on behalf of clients. It facilitates the clients to share data, information or any hardware and software resources. The clients typically connect to the server through the network but may run on the same computer. In the context of Internet Protocol (IP) networking, a server is a program that operates as a socket listener.[1]Servers often provide essential services across a network, either to private users inside a large organization or to public users via the Internet. Typical computing servers are database server, file server, mail server,print server, web server, gaming server, andapplication server.[2]Numerous systems use this client server networking model including Web sites and email services. An alternative model, peer-to-peer networking enables all computers to act as either a server or client as needed.Servers in a data center. Several servers are mounted on a rack and connected to a KVM switch. Usage The term server is used quite broadly ininformation technology. 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. While the existence of files on a machine does not classify it as a server, the mechanism that 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). This web server software can be runon any capable computer. For example, while a laptop 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, the machines role that places it in the category of server.In the hardware sense, the word servertypically designates computer models intended for hosting software applicationsunder the heavy demand of a networkenvironment. In this client–serverconfiguration, one or more machines, either a computer or a computer appliance, share information with each other with one acting as a host for the other[s].While nearly any personal computer 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, increased high-performance RAM, and increased storage capacity in the form of a larger or multiple hard drives. Servers also typically have reliability, availability and serviceability (RAS) and fault tolerancefeatures, such as redundancy in power supplies, storage (as in RAID), and network connections.Servers became common in the early 1990s as businesses increasingly began using personal computers to provide services formerly hosted on larger mainframes orminicomputers. Early file servers housed multiple CD-ROM drives, which were used to host large databaseapplications.[citation needed]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, a unit that combines hardware and software in an out-of-the-box packaging. Also produced were the Cobalt Qube and theRaQ. Simpler examples of such appliances include switches, routers, gateways, and print servers, all of which are available in a nearplug-and-play configuration.Modern operating systems such as Microsoft Windows or Linux distributions seem to be designed with a client–server architecture in mind. These operating systems attempt toabstract hardware, 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 languages must interact using an API.These operating systems may be able to run programs in the background called eitherservices or daemons. Such programs, such as the above-mentioned Apache HTTP Serversoftware, may wait in a sleep state for their necessity to become apparent. Since any software that provides services can be calleda server, modern personal computers can be seen as a forest of servers and clients operating in parallel.The Internet itself is also a forest of servers and clients. Merely requesting a web pagefrom 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 routers,modems, domain name servers, and various other servers necessary to provide us theworld wide web.The introduction of Cloud computing allows server storage and other resources to be shared in a pool and provides servers with a higher degree of fault tolerance. Hardware Requirement A rack-mountable server. Top cover removed to reveal the internal components.Hardware requirement for servers vary, depending on the server application. Absolute CPU speed is not quite as critical to a server as it is to a desktop machine[citation needed]. Servers duties to provide service to many users over a network lead to different requirements such as fast network connections and high I/O throughout. Since servers are usually accessed over a network, they may run in headless mode without amonitor or input device. Processes that are not needed for the servers function are not used. Many servers do not have a graphical user interface (GUI) as it is unnecessary and consumes resources that could be allocated elsewhere. Similarly, audio and USBinterfaces may be omitted.Servers often run for long periods without interruption and availability 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 rates in order to maximize uptime, 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 to justify the expense of entirely replacing the system with something more reliable. Servers may incorporate faster, higher-capacity hard drives, larger computer fans or water coolingto help remove heat, and uninterruptible power supplies 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. Hardwareredundancy—installing more than one instance of modules such as power suppliesand hard disks 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.[3]To increase reliability, most servers use memory with error detection and correction,redundant disks, 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 system administrators, their operating systems are also more tuned for stability and performance than for user friendliness and ease of use,Linux taking a noticeably larger percentage than for desktop computers.[citation needed]As servers are often noisy and they need a stable power supply, good Internet access, and increased security, it is usual to store them in dedicated server centers. This requires reducing the power consumption, as the extra energy used generates more heat thus causing the temperature in the room to exceed acceptable limits; hence normally, server rooms are equipped with air conditioning devices. Server casings are usually flat and wide (typically measured in rack units), adapted to store many devices next to each other in a server rack. Unlike ordinary computers, servers usually can be configured, powered up and down or rebooted remotely, using out-of-band management, typically based on IPMI.Many servers take quite a long time for the hardware to start up and load the operating system. Servers often do extensive pre-bootmemory testing and verification and startup of remote management services. The hard drive controllers 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 RAIDsystem 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.A server rack seen from the rear Wikimedia Foundationservers as seen from the front Wikimedia Foundationservers as seen from the rear Wikimedia Foundationservers as seen from the rear Operating systems Server-oriented operating systems tend to have certain features that make them more suitable for the server environment, such as[citation needed]GUI not available or optionalability 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 differentvolumes or devices,flexible and advanced networking capabilities,automation capabilities such as daemonsin UNIX and services in Windowstight 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.[4]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 common 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.[5]Windows and Mac OS X server operating systems are deployed on a minority of servers, as are other proprietary mainframeoperating systems, such as z/OS. The dominant operating systems among servers are UNIX-like open source distributions, such as those based on Linux and FreeBSD.[6] The rise of the microprocessor-based server was facilitated by the development of Unix to run on the x86 microprocessor architecture. TheMicrosoft Windows family of operating systems also runs on x86 hardware and, since Windows NT, have been available in versions suitable for server use.[7]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 applications andmiddleware platforms has also lessened the demand for specialist application servers.[citation needed] Types In a general network environment the following types of servers may be found.Application server, a server dedicated to running certain software applicationsCatalog server, a central search point for information across a distributed networkCommunications server, carrier-grade computing platform for communications networksCompute server, a server intended for intensive (esp. scientific) computationsDatabase server, provides database services to other computer programs or computersFax server, provides fax services for clientsFile server, provides remote access to filesGame server, a server that video game clients connect to in order to play online togetherHome server, a server for the homeMail server, handles transport of and access to emailMedia server, a specialized application server, usually enterprise class machine, providing video on demandMobile Server, or Server on the Go is an Intel Xeon processor based server class laptop form factor computer.Name server or DNSPrint server, provides printer servicesProxy server, acts as an intermediary for requests from clients seeking resources from other serversSound server, provides multimedia broadcasting, streaming.Stand-alone server, a server on a Windows network that neither belongs to nor governs a Windows domainWeb server, a server that HTTP clients connect to in order to send commands and receive responses along with data contentsAlmost the entire structure of the Internet is based upon a client–server model. High-levelroot 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]World Wide WebDomain Name SystemE-mailFTP file transferChat and instant messagingVoice communicationStreaming audio and videoOnline gamingDatabase serversVirtually every action taken by an ordinaryInternet user requires one or more interactions with one or more servers that operate on an inter-server level. Other services do not use dedicated servers; for example peer-to-peer file sharing, some implementations of telephony (e.g. Skype), and supplying television programs to several users (e.g. Kontiki, SlingBox)[citation needed]. 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 theUnited States.[9]To put this in context, this is less than the 6 billion cell phones in the world use to recharge their batteries. Moreover, this pales in comparison to double-digit uses like heating and cooling, domestic hot water, ranges, ovens, and clothes dryers, to name a few. Finally, to keep this use in perspective, the Smart2020 report estimates that ICT (Information and Communications Technology) saves more than 5 times its carbon footprint[10] in the rest of the economy by enabling efficiency. Size classes Sizes include[citation needed]:rack servertower serverminiature (home) serversmini rack serversblade serverMobile ServerUltra-Dense ServerSuper servers See also Home serverFile serverPrint serverMedia serverMobile Server References Tap to expand
Posted on: Fri, 16 Jan 2015 10:39:44 +0000
Trending Topics
Recently Viewed Topics
© 2015