Introducing the deep webin reference to:
"To get a more precise idea of the nature of this ‘Dark Continent’ involving the invisible and web search engines, read what Wikipedia has to say about the Deep Web. The figures are attention grabbers – the size of the open web is 167 terabytes. The Invisible Web is estimated at 91,000 terabytes. Check this out – the Library of Congress, in 1997, was figured to have close to 3,000 terabytes!"
- 10 Search Engines to Explore the Invisible Web (view on Google Sidewiki)