The low memory footprint (compared to other web servers), small CPU load and speed optimizations make lighttpd suitable for servers that are suffering load problems, or for serving static media separately from dynamic content. lighttpd is free software/open source, and is distributed under the BSD license. It runs natively on Unix-like operating systems as well as Microsoft Windows.

lighttpd supports the FastCGI, SCGI and CGI interfaces to external programs, permitting web applications written in any programming language to be used with this server. As a particularly popular language, PHP performance has received special attention. Lighttpd’s FastCGI can be configured to support PHP with opcode caches (like APC) properly and efficiently. Additionally, it has received attention from its popularity within the Python, Perl, Ruby and Lua communities. It is a popular web server for the Catalyst and Ruby on Rails web frameworks. Lighttpd does not support ISAPI.

Features

• Load-balancing FastCGI, SCGI and HTTP proxy support
• chroot support
• select()-/poll()-/epoll() based web server
• Support for more efficient event notification schemes like kqueue and epoll
• Conditional rewrites (mod_rewrite)
• SSL and TLS support, via OpenSSL.
• Authentication against an LDAP server
• RRDtool statistics
• Rule-based downloading with possibility of a script handling only authentication
• Server Side Includes support (but not server-side CGI ^[6])
• Flexible virtual hosting
• Modules support
• Cache Meta Language (currently being replaced by mod_magnet) using the Lua programming language
• Minimal WebDAV support
• Servlet (AJP) support (in versions 1.5.x and up)
• HTTP compression using mod_compress and the newer mod_deflate (1.5.x)
• Light-weight (less than 1 MB)
• Single-process design with only several threads. No processes or threads started per connection.

Apache is developed and maintained by an open community of developers under the auspices of the Apache Software Foundation. The application is available for a wide variety of operating systems, including Unix, GNU, FreeBSD, Linux, Solaris, Novell NetWare, AmigaOS, Mac OS X, Microsoft Windows, OS/2, TPF, and eComStation. Released under the Apache License, Apache is open-source software.

Apache was originally based on NCSA HTTPd code. The NCSA code has since been removed from Apache, as part of a rewrite.

Since April 1996 Apache has been the most popular HTTP server software in use. As of May 2011 Apache was estimated to serve 63% of all websites and 66% of the million busiest.

The most common use of web servers is to host web sites but there are other uses like data storage or for running enterprise applications.

The primary function of a web server is to deliver web pages on the request to clients. This means delivery of HTML documents and any additional content that may be included by a document, such as images, style sheets and scripts.

A client, commonly a web browser or web crawler, initiates communication by making a request for a specific resource using HTTP and the server responds with the content of that resource or an error message if unable to do so. The resource is typically a real file on the server’s secondary memory, but this is not necessarily the case and depends on how the web server is implemented.

While the primary function is to serve content, a full implementation of HTTP also includes ways of receiving content from clients. This feature is used for submitting web forms, including uploading of files.

Many generic web servers also support server-side scripting, e.g., Apache HTTP Server and PHP. This means that the behaviour of the web server can be scripted in separate files, while the actual server software remains unchanged. Usually, this function is used to create HTML documents “on-the-fly” as opposed to returning fixed documents. This is referred to as dynamic and static content respectively. The former is primarily used for retrieving and/or modifying information from databases. The latter is, however, typically much faster and more easily cached.

Web servers are not always used for serving the world wide web. They can also be found embedded in devices such as printers, routers, webcams and serving only a local network. The web server may then be used as a part of a system for monitoring and/or administrating the device in question. This usually means that no additional software has to be installed on the client computer, since only a web browser is required (which now is included with most operating systems).

The scope of web hosting services varies greatly. The most basic is web page and small-scale file hosting, where files can be uploaded via File Transfer Protocol (FTP) or a Web interface. The files are usually delivered to the Web “as is” or with little processing. Many Internet service providers (ISPs) offer this service free to their subscribers. People can also obtain Web page hosting from other, alternative service providers. Personal web site hosting is typically free, advertisement-sponsored, or inexpensive. Business web site hosting often has a higher expense.

Single page hosting is generally sufficient only for personal web pages. A complex site calls for a more comprehensive package that provides database support and application development platforms (e.g. PHP, Java, Ruby on Rails, ColdFusion, and ASP.NET). These facilities allow the customers to write or install scripts for applications like forums and content management. For e-commerce, SSL is also highly recommended.

The host may also provide an interface or control panel for managing the Web server and installing scripts as well as other modules and service applications like e-mail. Some hosts specialize in certain software or services (e.g. e-commerce). They are commonly used by larger companies to outsource network infrastructure to a hosting company.