https://help.superhosting.bg/en/cgi-common-gateway-interface-fastcgi.html First, the two protocols: CGI scripts is a way how to run a server side script when a HTTP request comes; this has nothing to do with PHP FastCGI is a "better CGI" - CGI is known to be slow, Fast CGI is a different approach with much faster results; this has also nothing to do with PHP. Now the PHP related things: mod_php is running a PHP as Apache module - that is PHP request is run under Apache process with everything that goes with it - Apache processes are defined by Apache configuration, PHP is run with Apache permission etc. PHP-FPM is PHP's FastCGI implementation; PHP-FPM runs as a standalone FastCGI server and Apache connects to the server using Apache's module, usually mod_fcgid or mod_fastcgi; I personally think this is much better than running as mod_php, but it depends on your requirements and is also a little more complex; in this configuration, permission, pr...