This talk will give you a brief overview of the reasons why PHP is designed as it is, and its goals in answering the needs of Web developers. PHP 4.0 represented a change in how the code was executed, allowing the entire script to be read and compiled before execution..The design goals in creating the PHP 4.0 scripting engine (Zend Engine) were: fast execution, modular structure, compatibility with PHP 3, independence from PHP, and extendibility through a comprehensive API. New features that will be reviewed briefly include reference counting, Web server independence, high performance API, independent output layer and UNIX build process. Further, the talk will discuss the inner workings of PHP, and how the different modules interact. We will cover the information flow through: Browser, Web Server, PHP Web Server Interface, Zend Engine, Web Server Disk, PHP Modules, and back through the Web Server Interface and to the Browser.