APC, or Alternative PHP Cache, is a PHP module which caches the output code of database-driven script software applications. Dynamic PHP sites hold their content in a database which is accessed whenever a visitor loads a page. The content which should be displayed is gathered and the code is parsed and compiled before it is delivered to the website visitor. These actions take some processing time and involve reading and writing on the server for every single page which is accessed. While this can't be avoided for sites with constantly changing content material, there are numerous sites that offer the exact same content on many of their webpages all the time - blogs, informational portals, hotel and restaurant websites, etc. APC is extremely useful for this kind of Internet sites as it caches the previously compiled code and shows it each time visitors browse the cached pages, so the code doesn't need to be parsed and compiled repeatedly. This will not only greatly reduce the server load, but it'll also increase the speed of any Internet site many times.