How the Wayback Machine Works tells us how How the Wayback Machine Works.

There are 10 billion Web pages, collected over five years, they say a book is a megabyte, and the Library of Congress has 20 million books, that\’s 20 terabytes. The total gathering speed when everything is moving is about 10 terabytes a month, or half a Library of Congress a month.

\”How big is 100 terabytes? Kahle, who serves as archive director and president of Alexa Internet, a wholly-owned subsidiary of, says it\’s about five times as large as the Library of Congress, with its 20 million books.\”