The Zend Engine is an open-source scripting engine, commonly known for the important role it plays in the web automation language PHP. It was originally developed by Andi Gunmans and Zeev Suraski while they were students at the Technion (Israel Institute of Technology). They later founded a company called Zend Technologies - the name is a portmanteau of their forenames.
The first version of the Zend engine appeared in 1999 alongside PHP version 4. It was written as a highly optimized modular back-end, which for the first time could be used in applications outside of PHP. The performance, reliability and extensibility of the engine played a significant role in increasing the popularity of PHP.
