APC, which means Alternative PHP Cache, is a framework used for caching the compiled source code of a script application, which can boost a database-driven site several times. When a PHP webpage is accessed, the script pulls the website content which has to be displayed from a database, parses and compiles the program code, and then the result is displayed to the site visitor. While this is necessary for sites with frequently changing content, it is a total waste of processing time and system resources for an Internet site that doesn't change, such as an informational portal which displays the very same content on a regular basis. Once the webpages for such a site are compiled, APC caches them and delivers them any time a visitor opens them. Since this saves the time to get content from the database and to parse and compile the program code, the site will load much faster. APC is really useful in particular for scripts with large source code.