I noticed on Manual:Installation guide that PHP is a requirement, but no mention of it is on this page. A section on installing for Windows and *nix would be helpful.
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Topic on Manual talk:Installing MediaWiki
PHP is mentioned in Manual:Installation requirements with all the needed versions and modules. Apart from that, installation of PHP is out of scope here since it's a generic piece of software and php.net website has updated manuals about its installation on different platforms.