Update: this article is for Ubuntu Dapper Drake (6.06). If you are using later versions, or other Linux distributions, then visit the following links: Installing PHP APC on GNU/Linux Gusty Gibbon 7.10 and (Debian). Installing PHP APC on GNU/Linux CentOS 5. APC is a op-code cache for PHP that eliminates the parsing and compiling of script(s) for every page hit. Unlike Zend, it is truly free, and se