APC (PHP Opcode Cache)

APC, or Alternative PHP Cache, is a PHP module which caches the output code of database-driven script software applications. Dynamic PHP sites save their content in a database which is accessed whenever a visitor opens a webpage. The content which has to be viewed is gathered and the code is parsed and compiled before it is delivered to the site visitor. All of these actions take some processing time and include reading and writing on the server for each page which is opened. While this can't be avoided for sites with regularly changing content, there're various sites which have the same content on a number of of their webpages at all times - blogs, info portals, hotel and restaurant sites, etcetera. APC is very useful for such sites since it caches the already compiled code and displays it any time visitors browse the cached pages, so the code doesn't have to be parsed and compiled repeatedly. This will not only lower the server load, but it'll also raise the speed of any site several times.