MongoDB 4 Quick Start Guide

MongoDB PHP architecture

The big difference between the old and new drivers is that the new driver is based upon libmongoc (https://github.com/mongodb/mongo-c-driver) and libbson (https://github.com/mongodb/mongo-c-driver/tree/master/src/libbson). Also, this extension provides support not only for PHP 5, but PHP 7 and even HHVM (https://hhvm.com/, a PHP code compatible abstraction layer used by Facebook). Finally, a library is provided which uses the mongodb extension, and provides all of the functionality which used to be included monolithically in the old extension. This means that MongoDB PHP developers are free to focus on adding value to PHP rather than having to do the low level work of connecting to MongoDB and extracting results.  ...