APC, or Alternative PHP Cache, is a PHP module that caches the output code of database-driven script software applications. Dynamic PHP sites save their content inside a database that 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's delivered to the website visitor. All of these actions take some processing time and involve reading and writing on the web server for every single page that is loaded. While this cannot be avoided for websites with regularly changing content material, there're many sites which feature the same content on a number of of their webpages all of the time - blogs, informational portals, hotel and restaurant Internet sites, etcetera. APC is really useful for such Internet sites since it caches the already compiled code and displays it every time visitors browse the cached webpages, so the code does not have to be parsed and compiled again. This will not only greatly reduce the server load, but it'll also increase the speed of any site many times.