Complex sentence: PHP's single-request-per-script-execution model, and the fact the Zend Engine is an interpreter, leads to inefficiency; as a result, various products have been developed to help improve PHP performance.
Split into simpler sentences: PHP's single-request-per-script-execution model, and the fact the Zend Engine is an interpreter, lead to inefficiency. As a result, various products have been developed to help improve PHP performance.