how search in wikipedia works?

I am a beginer in web technologies so sry if its a lame question.

Wikipedia and other such sites which host million of web pages. How search works in these pages. Do they store all 开发者_高级运维html pages in memory? if yes What are the possible data structure used to store all the html pages to store in-memory and do search among those so fast?

Wikipedia uses the Lucene full text search engine. Another popular full text search engine is Sphinx.

They have quite detailed descriptions of what exactly they got.

Wikipedia: Web search
How Internet Search Engines Work How Search Engines Work (rather nice explanation)