APC, or Alternative PHP Cache, is a PHP module which caches the output code of database-driven script software applications. Dynamic PHP Internet sites save their content within a database which is accessed whenever a visitor loads a page. The content which has to be displayed is gathered and the code is parsed and compiled before it is delivered to the site visitor. These actions need some processing time and require reading and writing on the server for every single page which is loaded. While this can't be avoided for sites with regularly changing content, there are numerous sites that present the same content on a number of of their pages constantly - blogs, info portals, hotel and restaurant websites, etc. APC is extremely useful for this kind of Internet sites because it caches the previously compiled code and shows it every time visitors browse the cached pages, so the code doesn't have to be parsed and compiled all over again. Not only will this lower the server load, but it'll also increase the speed of any website many times.