Opcode Caching

The code which you wright in PHP the PHP compiler convert that code in OPCODE.
The best you can also add OPCODE caching in your PHP applications.
The Few opcode caching listed bellow.
1. eaccelerator [eaccelerator]
2. XCache [http://xcache.lighttpd.net/]
3. APC [http://in3.php.net/apc/]

Using this tools you can cache PHP Opcode.
The Opcode caching improves your application performance.