What is the CGI mechanism?

Question

Apache HTTP Server

Please explain in detail to the noob what are the differences between the CGI mechanism and FastCGI and why Apache needs them at all, I did not fully understand on the wiki.

Answer 1

In VERY short terms: CGI starts a new process every time it needs to execute code. FastCGI forks several processes at startup, which always hang in memory and receive code to execute.