Web server is a server that accepts HTTP requests from clients, usually a web browser, and give them HTTP responses, usually an HTML page, image, file, media stream or other data.
The client, which is typically a web browser, sends requests for resources (designated URL addresses). In response, the web server transmits the requested data to the client. This exchange takes place via HTTP.
Web servers can have a variety of additional features, for example:
- automation of web pages;
- logging visitors’ access to resources;
- authentication and authorization;
- support for dynamically generated pages;
- HTTPS support for secure connections with clients.
Often on a computer with a web server is installed as a mail server.
On August 2011 the most popular web server, occupying more than 65% of the market, is an Apache – a free web server, the most commonly used in UNIX-like operating systems.
Some other well-known web servers :
- IIS on with Microsoft, distributed with the Windows Server operating system.
- nginx – free web server developed by Igor Sysoev.
- lighttpd – free web server.
- Google Web Server – a web server based on Apache and modified by Google.
- Resin – free web application server.
- Cherokee – free web server operated only through the web interface.
- Rootage – a web server written in java.
- THTTPD – simple, small, fast and secure web server.
Clients may use different programs and devices to access the web servers:
web browser running on a desktop computer or portable device (such as a Pocket PC);
a variety of programs, independently accessing web servers for updates, or other information (for example, an anti-virus may periodically request from a specific web server updates for its databases);
mobile phone, accessing the resources of a web server using the WAP protocol;
other digital devices or appliances.