APC, or Alternative PHP Cache, is a PHP module which caches the output code of database-driven script software apps. Dynamic PHP sites keep their content in a database that is accessed whenever a visitor loads a webpage. The content which has to be displayed is gathered and the code is parsed and compiled before it's delivered to the visitor. All these actions need some processing time and require reading and writing on the hosting server for every single page that is accessed. While this can't be avoided for websites with regularly changing content, there are a lot of Internet sites that present the same content on many of their webpages constantly - blogs, informational portals, hotel and restaurant websites, and many others. APC is extremely useful for such sites because it caches the previously compiled code and displays it whenever visitors browse the cached webpages, so the code does not have to be parsed and compiled repeatedly. Not only will this greatly reduce the server load, but it will also increase the speed of any website a few times.