What database does Google use?

I was wondering what database system does google use. Oracle or MySQL? These two are the names came into my mind then. But just after little googling I found something much more interesting.

Google actually does not use any of the database systems available at market. Sure they use Oracle and MySQl (modified versions) for some of their services but neither of those contributes to their Search Engine. They have developed a storage system for their search engine(really a google job!!!). This is called Big Table. Google has been using it since early 2005.

This is a distributed storage system for managing structured data that is designed to scale to a very large size: petabytes of data across thousands of commodity servers.

Bigtable is the basis of Google's search technology, as well as many other applications such Google Finance, Google Maps and Google Earth. These applications place very different demands on Bigtable, both in terms of data size (from URLs to web pages to satellite imagery) and latency requirements (from backend bulk processing to real-time data serving).

Bigtable was developed with very high speed, flexibility and extremely high scalability in mind. A Bigtable database can be petabytes in size and span thousands of distributed servers.

Google released it in May 2008 as part of Google App Engine. As is typical with Google offerings, Bigtable is free to use, and the service is described as "in beta," even though Google has been using Bigtable internally for more than three years.

So why not dig deeper to find more about this....let me know if any of you get lucky with something interesting.