The Wayback Machine is a digital archive of the World Wide Web and information on the internet. It was created by the Internet Archive, a nonprofit organization, by Brewster Kahle and Bruce Gilliat.
It has been archiving cached pages of websites since 1996. To create the Wayback Machine, Kahle and Gilliat developed software to crawl and download all publicly accessible World Wide Web pages, the Gopher hierarchy, the Netnews (Usenet) bulletin board system, and downloadable software.
At first, archived information were kept on digital tapes. But when the archive was five years old in 2001, the Wayback Machine was unveiled and opened to public.
Wayback Machine's crawlers collect information from websites that are publicly available on the internet. It doesn't include all the information because much of the data is restricted by the publisher or stored in databases that can't be accessed by the crawlers. Websites can also restrict the crawlers from indexing their pages using the robots.txt exclusion.
Each websites that have been indexed, are re-recrawled after a few weeks or a few months so a new copy of the version can be collected.
The intention of the Wayback Machine is to archive contents of the web that otherwise would be lost when a website is changed or shuts down. Its larger goal is to archive the entire internet into its database.