On DZone.com today there's a post covering the different kinds of handlers that can execute PHP - those pieces of code that work with the web servers we use every day to interpret and execute PHP code.

PHP Handlers? mod_php? FPM? How do we make sense of the inner workings of PHP outside of our lines of code? We know we can run PHP on the server to build web applications swiftly, but how can we optimize our environment and configurations to reach maximum scale? We know that PHP has its drawbacks for not being asynchronous or event-driven, which is all the more reason to ensure maximum optimization. The impact of your server environment on your PHP application performance can be more than you think you can afford. A careful examination of your PHP ecosystem will help you avoid suffering performance loss in areas you can otherwise solve for easily.

They provide a brief summary of what PHP handers, well, handle and where they fit in the overall architecture of execution. They then get into the details on some of them:

• CGI – mod_cgi
• suPHP – mod_suphp
• DSO – mod_php
• FastCGI – mod_fcgid
• FPM (FastCGI Process Manager) – php-fpm

Included in each is an overview of how it works and some of the main advantages (and disadvantages) of their use. He also mentions two of the most popular web servers that work with these handlers: Apache and Nginx.