PHP includes various free and open-source libraries in its source distribution, or uses them in resulting PHP binary builds. PHP is fundamentally an Internet-aware system with built-in modules for accessing File Transfer Protocol servers and many database servers, including MySQL, Microsoft SQL Server and SQLite (which are an embedded database), and others. Numerous functions familiar to C programmers, such as those in the stdio family, are available in standard PHP builds too. PHP has a direct module interface called Server Application Programming Interface (SAPI). It is supported by many web servers including Apache HTTP Server and iPlanet.
Originally PHP was designed to create dynamic web pages but now it focuses mainly on server-side scripting. It is similar to other server-side scripting languages providing dynamic content from a web server to a client, such as Microsoft's ASP.NET and mod_perl. PHP has also involved the development of many software frameworks that provide building blocks and a design structure to promote rapid application development (RAD).