FastCGI is an extension to Common Gateway Interface that increases speed. Instead of creating a new process every time a page is reloaded, FastCGI will use the same process, queuing up requests. This increases startup speed, at the expense of forcing users to wait for the previous requests to finish. FastCGI also allows programs to get the web server to do certain operations, like reading in a file, before the request is handed over.

Environment information and page requests are sent from the web server to the process over a Transport_Control_Protocol (for remote processes) or a Unix domain sockets (for local processes.) Responses are returned from the process to the web server over the same connection. The connection is closed at the end of a response, but the web server and the process are left standing.

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