PHP 4

By the winter of 1998, shortly after PHP 3.0 was officially released, Andi Gutmans and Zeev Suraski had begun working on a rewrite of PHP’s core. The design goals were to improve performance of complex applications, and improve the modularity of PHP’s code base. Such applications were made possible by PHP 3.0’s new features and support for a wide variety of third party databases and APIs, but PHP 3.0 was not designed to handle such complex applications efficiently.

The new engine, dubbed ‘Zend Engine’ (comprised of their first names, Zeev and Andi), met these design goals successfully, and was first introduced in mid 1999. PHP 4.0, based on this engine, and coupled with a wide range of additional new features, was officially released in May 2000, almost two years after its predecessor. In addition to the highly improved performance of this version, PHP 4.0 included other key features such as support for many more web servers, HTTP sessions, output buffering, more secure ways of handling user input and several new language constructs.