A server ( Engl. : To serve = use ) is a program that the contact of a client waiting for a specific service to meet him. Communication takes place according to the client-server model . The service of the server is specific to the server, so that there is a separate server for each service. The service provided by the server is called a service , and the data exchange between client and server is determined by a service-specific protocol .
Computers that run server software are called hosts . The meaning of server treated here as software that offers a service to users is the original correct definition in computer science . That the host computer itself as a server called will, is added later by the usage of secondary importance, but has become more common in everyday language than the original, correct definition.
- The World Wide Web consists of web pages that are transferred from servers to the web browser using the Hypertext Transfer Protocol (HTTP) . Servers that implement HTTP , i.e. H. who master it are called HTTP servers or web servers . Access is via HTTP clients (web browsers). With a variant of HTTP, HTTPS , websites are also transmitted, whereby the transmission path is protected by encryption.
- Servers that implement a file transfer protocol are commonly referred to as file , data, or file servers . The data transfer protocols most frequently used for this on the Internet are FTP and SFTP . In local computer networks ( LAN ), for example within companies, SMB or NFS is usually used as the protocol.
Availability and Clustering
A server either runs permanently or is started upon request from a client ( Unix : see daemon mode , inetd ). In order to increase the reliability and performance, several servers can be interconnected as a cluster . These can be distributed on one or on several hosts . If one or more servers fail, the remaining servers take over the client's request.
Known server types
|Authentication server||RADIUS||contains a database of user IDs, passwords, IP addresses, and other information.|
|Chat server||IRC , XMPP||communicates the data among chat participants .|
|File server||FTP , SFTP , WebDAV||allow the transfer of files .|
|NFS , SMB||allow editing of remote files via a client. In general, concurrent access is also possible. In contrast to a file transfer service, not all of the files are transferred, only the operations performed on the files and the specific data belonging to them.|
|Database server||CLI ( ODBC , JDBC ), DBI||manage one or more database systems.|
|Digital media server||DMS||provide media content (e.g. films, pictures, music).|
|Print server||LPDP||convey access to printers .|
|DHCP server||DHCP||assign computers in the network u. a. dynamically assign IP addresses.|
|Game server||various||are used for online games.|
|Mail server||SMTP , POP3 , IMAP||are used to send and receive e-mails .|
|Map server||provide web services ( geospatial services ) specialized in spatial data .|
|Name server||DNS||The DNS root name servers are the most important name servers in the domain name system .|
|News server||NNTP||NNTP is a protocol for exchanging text messages on Usenet .|
|Proxy server||make cached information available to other computers.|
|Streaming server||various||can for example broadcast Internet radio (e.g. VLC ).|
|Terminal server||RDP , VNC||provide other computers (mostly thin clients ) with an emulated work environment.|
|Web server||HTTP / HTTPS||deliver websites to web clients.|
|Time server||NTP||are used to synchronize computer clocks.|
Servers expect clients to contact them on certain ports . At least one port is assigned to each server. A certain server is addressed with one of its port numbers in connection with an address of its host. Communication takes place via sockets .
- Host (information technology)
- Douglas E. Comer: Computer Networks and Internet. Pearson Studies, ISBN 3-8273-7023-X
- Craig Hunt: TCP / IP. O'Reilly, ISBN 3-89721-179-3
- Link catalog on the topic of Managed Dedicated Server at curlie.org (formerly DMOZ )
- Link catalog on the topic of dedicated servers at curlie.org (formerly DMOZ )