What OS does Google run on its servers?

Google uses a customized Linux operating system that is optimized for use in massive commodity-based hardware clusters.


They are designed to be fault tolerant and fail over with many multiple redundancies both inside their server rooms and regionally. This way when one of those commodity-based systems crap out they simply ignore it until somebody has time to replace it. This way they can have very large datacenters and manage it without large amounts of effort.

They don't use SQL databases or RAId or anything like that for their search engine stuff. Simply because those sort of things don't scale very well. Instead they have a specialized google-specific file system with super-secret algorythms and whatnot to manage all of it.