FastCGI is an enhancement to the existing CGI (Common Gateway Interface), which is a standard for interfacing external applications with Web Servers. Like CGI, FastCGI applications run in separate, isolated processes. Some of the advantages of using FastCGI are as follows:
Enables applications to persist between client requests, eliminates application start up overhead, and allows the application to maintain state between client calls.
Enables applications to reside on remote systems (a different system from where the Web Server is running).
Enables additional flexibility in application functionality, with explicit support for applications that do client authentication and filtering of input.
Allows the administrator to restrict the impact on the system that is caused by the FastCGI servers.
FastCGI plug-in allows Web Server to safely work with popular third-party dynamic content generation technologies (such as Perl and Python) in a scalable way.
For more information on FastCGI, refer to the specification at http://www.fastcgi.com/devkit/doc/fcgi-spec.html.