[2] It was originally developed by Andi Gutmans and Zeev Suraski while they were students at the Technion – Israel Institute of Technology.

The Zend Engine provides memory and resource management, and other standard services for the PHP language.

Its performance, reliability and extensibility played a significant role in PHP's increasing popularity.

This was followed by Zend Engine 3, originally codenamed phpng, which was developed for PHP 7 and significantly improves performance.

Zend itself really forms only the language core, implementing PHP at its very basics with some predefined functions.