Zend Optimizer uses multi-pass code optimizations to double the running speed of PHP applications. This is done by running an optimization of the code created by the run-time compiler, before the code is executed. The standard Zend run-time compiler used by PHP 4 is extremely fast, generating code that is usually 2 to 10 times faster than the equivalent code in PHP 3. Using the Zend Optimizer typically executes another 10% to 50% faster over standard PHP 4.