What is a server?

The term ‘server’ is used am­bigu­ously in computer science. A server refers to both a computer that provides resources over a network and the program that runs on this computer.

Defin­i­tion of server

You can dis­tin­guish between the following two server defin­i­tions:

• Server defin­i­tion (hardware): A hardware-based server is a physical machine connected to a computer network, running one or more software-based servers along with 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.
• Server defin­i­tion (software): A software-based server is a program that offers a specific service, which can be utilised by other programs, called clients, locally or over a network. The available service depends on the type of server software. The found­a­tion of com­mu­nic­a­tion is the client-server model. Service-specific trans­mis­sion protocols are used in data exchange.

How does a server work?

The provision of server services over a computer network is based on the client-server model. This concept allows tasks to be dis­trib­uted across different computers and made in­de­pend­ently ac­cess­ible to multiple end users. Each service available over a network is offered by a server (software) that is always on standby. This ensures that clients like web browsers or email programs can actively access the server and utilise the service as needed at any time.

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What are the different types of servers?

How a client and server com­mu­nic­ate depends on the specific service and is de­term­ined by a specific trans­mis­sion protocol. This principle can be il­lus­trated using the example of common server types:

• Web server: The primary task of a web server is to store, process, and deliver web pages to clients like web browsers or search engine crawlers. Com­mu­nic­a­tion between server (software) and client is based on the Hypertext Transfer Protocol (HTTP) or its encrypted version HTTPS. Typically, HTML documents and their embedded elements like images, stylesheets, or scripts are trans­mit­ted. Common web servers include the Apache HTTP Server, Microsoft Internet In­form­a­tion Services (IIS), and NGINX.
• File server: A file server is used for centrally storing files that are to be accessed by various clients over a network. Companies rely on such file man­age­ment to allow multiple work­groups access to the same files. A file server prevents conflicts due to different local file versions, enables automatic file ver­sion­ing, and provides a central backup of all company data. If access to the file server occurs over the Internet, transfer protocols like 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.
• Email server: An email server consists of several software modules that work together to receive, send, forward, and store emails for retrieval. Typically, the Simple Mail Transfer Protocol (SMTP) is used. Users who want to access an email server need an email client that retrieves messages from the server and makes them available in the email inbox. This retrieval occurs 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. Popular software solutions include Oracle, MySQL, Microsoft SQL Server, Post­gr­eSQL, and DB2. Database servers typically assist web servers in storing and de­liv­er­ing data.
• Game server: A game server is a server (software) spe­cific­ally set up for online mul­ti­play­er games. Game servers manage the game’s data and enable syn­chron­ous in­ter­ac­tion with the virtual world. A game server’s hardware can either be hosted in a spe­cial­ised provider’s data centre or installed locally within a home network.
• Proxy server: A proxy server serves as a com­mu­nic­a­tion interface in computer networks. Acting as an in­ter­me­di­ary, the proxy server receives requests from the network and forwards them using its own IP address. Proxy servers are used to filter com­mu­nic­a­tion, control bandwidth, increase avail­ab­il­ity through load balancing, or cache data. Ad­di­tion­ally, a proxy server enables extensive an­onymisa­tion as the client’s IP address remains hidden behind the proxy.
• DNS server: DNS or name servers are used for name res­ol­u­tion in a network. For the World Wide Web, DNS servers are crucial as they translate hostnames like www.example.com into the cor­res­pond­ing IP address. More in­form­a­tion on name servers and the Domain Name System can be found in the in-depth article on DNS.
• GPU server: GPU servers are spe­cial­ised servers that use powerful graphics pro­cessors (GPUs) instead of just CPUs to process compute-intensive tasks faster. They are primarily used in ap­plic­a­tions involving ar­ti­fi­cial in­tel­li­gence, machine learning, 3D rendering, or sci­entif­ic sim­u­la­tions. By pro­cessing many data streams in parallel, GPUs can sig­ni­fic­antly ac­cel­er­ate complex cal­cu­la­tions. Compared to tra­di­tion­al servers, GPU servers offer sub­stan­tially higher computing power for spe­cial­ised workloads.

The­or­et­ic­ally, different types of servers can be hosted on the same physical machine. However, it is common to have each server housed on a stan­dalone computer or even dis­trib­uted across multiple computers. This helps prevent the hardware load of one service from affecting the per­form­ance of other services.

What does server hosting mean?

While pur­chas­ing their own server hardware might be worth­while for large companies, freel­an­cers and in­di­vidu­als looking to implement their own server projects typically rely on rented resources. Spe­cial­ised providers offer rental servers in various hosting models where users do not need to maintain the physical machine. The product range includes dedicated servers, whose hardware com­pon­ents are ex­clus­ively available to one user, and shared hosting packages, where multiple virtual customer servers are hosted on a common hardware basis.