Enable Zend OPcache for PHP 5.5 or Install ZendOpcache for PHP 5.3 or PHP 5.4
Zend Opcache is part of PHP 5.5, however, it's not enabled by default. It's a successor to APC cache--meaning APC cache is never going to be compatible with PHP 5.5 or higher
Opcache is also around 10% faster than APC, and more stable.
However, if you're on PHP 5.3 or PHP 5.4, you can still use ZendOpCache, and it should still be a bit faster than APC
Enable OpCache (part of with PHP 5.5)
vi /usr/local/lib/php.ini
Paste this under your extension_dir