You have two options when installing PHP: use it as a CGI executable, or use it as an Apache/ISAPI module. Although there are advantages in favour of both options, running PHP as a module is overwhelmingly favourable when it comes to performance, as all of PHP and its extension modules reside in memory as opposed to being loaded with every request.
From a purely performance-motivated point of view you would be crazy to run PHP as a CGI executable.
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