(PHP 4 >= 4.0.2, PHP 5, PHP 7) Returns information about the operating system PHP is running on

(PECL bcompiler >= 0.5) Writes a defined constant as bytecodes

(PHP 5 >= 5.6.0, PHP 7, PECL ZendOpcache >= 7.0.4) Tells whether a script is cached in OPCache