The term “server” (English for servant) is used ambiguously in computer science. A server is both a computer that provides resources over a network and the program that runs on that computer. Accordingly, there are two different server definitions:
Definition server (hardware): A hardware-based server is a physical machine integrated into a computer network on which one or more software-based servers run in addition to the operating system. An alternative term for a hardware-based server is “host”. In principle, any computer with server software can be used as a host.
Definition Server (Software): A software-based server is a program that offers a special service that can be used by other programs, so-called clients, locally or over a network. Which service is available depends on the type of server software. Communication is based on the client-server model. Service-specific transmission protocols are used for data exchange.
How does a server work?
The provision of server services via a computer network is based on the client-server model. This concept makes it possible to distribute tasks to different computers and make them accessible to several end users independently of each other. Every service that is available over a network is provided by a server (software) that is permanently on standby. This is the only way to ensure that clients such as web browsers or e-mail programs can actively access the server at any time and use the service as needed.
Which servers are available?
How client and server communicate depends on the respective service and is determined by a specific transmission protocol. This principle can be illustrated by the example of common types of servers:
web servers: The primary task of a web server is to store and prepare web pages and deliver them to clients such as web browsers or search engine crawlers. The communication between server (software) and client is based on the Hypertext Transfer Protocol (HTTP) or its encrypted variant HTTPS. As a rule, HTML documents and the elements included in them, such as images, style sheets or scripts, are transferred. Common web servers are the Apache HTTP Server, Microsoft Internet Information Services (IIS) or Nginx.
file server: A file server is used for the central storage of files that are to be made available to various clients over a network. Companies rely on this type of file management to give several workgroups access to the same files. A file server prevents conflicts due to different local file versions, enables automatic versioning of files and centralized backup of all company data. If the file server is accessed via the Internet, transfer protocols such as FTP (File Transfer Protocol), SFTP (Secure File Transfer Protocol), FTPS (FTP over SSL) or SCP (Secure Copy) are used. In local computer networks (LAN), the protocols SMB (Server Message Block) and NFS (Network File System) have become established.
mail server: A mail server consists of several software modules whose interaction makes it possible to receive, send, forward and hold e-mails ready for retrieval. Usually the Simple Mail Transfer Protocol (SMTP) is used for this purpose. Users who want to access a mail server need an e-mail client that retrieves the messages from the server and makes them available in the e-mail mailbox. This retrieval is done via IMAP (Internet Message Access Protocol) or POP (Post Office Protocol).
Database server: A database server is a computer program that allows other programs to access one or more database systems over a network. Corresponding software solutions with high market share are Oracle, MySQL, Microsoft SQL Server, PostgreSQL and DB2. Database servers generally support web servers in storing and delivering data.
game servers: A game server is a server (software) that is set up especially for online-based multiplayer games. Game servers manage the data of the online game and enable synchronous interaction with the virtual world. The hardware base of a game server can be located in the data center of a specialized provider or be provided locally in the home network.