Manual:MediaWiki architecture

Because the documentation in the source tree is sparse and the code is scarier, here's some info for new developers on generally how the MediaWiki software works.

General architecture:

web clients           user layer |     Apache webserver         network layer |           PHP MediaWiki's PHP scripts     logic layer / | \        /   |   \ filesystem  |  memcached      data layer |            |      MySQL database

See also: How to become a Wikipedia hacker