Google is normally uber-secretive about the size of its search indexes, but the official Google blog did drop a fascinating hint this week: Google is now indexing more than one trillion unique URLs. Of course, that makes the core database the company stores even larger:
This graph of one trillion URLs is similar to a map made up of one trillion intersections. So multiple times every day, we do the computational equivalent of fully exploring every intersection of every road in the United States. Except it'd be a map about 50,000 times as big as the U.S., with 50,000 times as many roads and intersections.
All of which is good reason to be grateful that Google's doing it, so you don't have to. [The Official Google Blog]