19.1 The World Wide Web Electronic hypertext contains links to
expanded or information embedded at relevant points in a
document. The links are analogous to footnotes in a traditional
paper document, but the electronic nature of these documents
allows easier physical access to the links. As early as 1945,
Vannevar Bush proposed linked systems for documents on
microfiche , but electronic hypertext systems did not take hold
until the 1960s and 1970s. In 1980, Tim Berners-Lee wrote a
notebook program for CERN called ENQUIRE that had bidirectional
links between nodes representing information. In 1989, he
proposed a system for browsing the CERN Computer Center's
documentation and help service. Tim Berners-Lee and Robert
Cailliau developed a prototype GUI browser-editor for the system
in 1990 and coined the "World Wide Web." The initial system was
released in 1991. At the beginning of 1993 there were 50 known
web servers, a number that grew to 500 by the end of 1993 and to
650,000 by 1997. Today, web browsers have