Apache HTTP Server is web server software developed by Robert McCool in 1995. Apache is written in C and runs operating system similar to Unix. Its open source system played an important and essential role of the development of the World Wide Web as we know it today. Because of it is an open source software, Apache is highly flexible and is available for use on many operating systems, such as Windows, Linux, and Mac OS. Apache currently serves over half of all websites, making it the world’s most popular software for HTTP serving.
With it’s flexible nature, Apache offers a number of language interfaces, such as Perl and PHP, which makes it a much more versatile web server. Because Apache is licensed as an open source software, is is freely distributed. Users can make modifications and changes as the see fit, and any software that uses Apache as its source code is held under the same license. This has led to the development of several thousand projects, available under the terms of the license.
In terms of performance, Apache HTTP Server compares very well to other web servers. The big difference that Apache provides is MultiProcessing Modules or MPMs, which are process-based rather than event-based. This allows for more reliability and consistency as opposed to higher performance.