Detecting Server API (CGI or Apache) at runtime?

Hi all, is there a way to tell at runtime if PHP is running as an Apache module or through CGI? phpinfo() shows this piece of information ("Server API" on the first page). But is it available as a server variable or a constant or whatever? I want to know this because I want to set the HTTP status code for a PHP script, and AFAICT this has to be done differently, depending on the server API: header("HTTP/1.1 304 Not modified"); for the Apache module header("Status: 304 Not modified"); for the CGI interface If this can be done with the same PHP code on both server APIs, that would solve my problem too. Thanks in advance, Richard