Server (software)

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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.


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

Server type Logs Explanation
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 .

See also


Web links