Google's index has been in memory for most of its life now: http://glinden.blogspot.com/2009/02/jeff-dean-keynote-at-wsdm-2009.html http://glinden.blogspot.com/

Google's index has been in memory for most of its life now: http://glinden.blogspot.com/2009/02/jeff-dean-keynote-at-wsdm-2009.html http://glinden.blogspot.com/2009/02/jeff-dean-keynote-at-wsd... It's actually more complicated than just a single static index, which is also why it's unrealistic to expect a search engine to be deterministic at scale.