PmWiki generates web pages (though generating pdf files and other formats is also possible). So in order to see its results, one needs a web browser. To make it serve those pages, PmWiki runs on top of an operating system (OS), under a web web server, and using the php scripting language. The lists below address all these elements.
When installing PHP for PmWiki on IIS do you recommend IIS ISAPI or IIS CGI?
Use IIS ISAPI