3
I'm not that conversant with the technology, but I don't believe it's emulation. To quote something that pops up on a number of sites: "Using PHP as a CGI binary is an option for setups that for some reason do not wish to integrate PHP as a module into server software (like Apache), or will use PHP with different kinds of CGI wrappers to create safe chroot and setuid environments for scripts. This setup usually involves installing executable PHP binary to the web server cgi-bin directory."
Michael