On Jan. 1, 1983, the Internet Protocol that we use today became the only approved way to move data on the young Internet. This important milestone set the stage for a global peer-to-peer network, where every computer was equally able to exchange information with any other computer. Higher-level protocols for transferring files, logging into remote computers, and exchanging mail, all followed the same philosophy. Had the Internet accepted multiple incompatible protocols, today's World Wide Web likely would not exist.

In a Dec. 15, 2002 mailing list posting, Bob Braden, who helped design the File Transfer Protocol (FTP) and the Transmission Control Protocol (TCP), described how worrisome the 1983 transition was: "People sometimes question that any geeks would have been in machine rooms on January 1. Believe it!! Some geeks got very little sleep for a few days (and that was before the word "geek" was invented, I believe)."

Research into the Internet's precursor, the ARPANET, dates to the late 60's and early 70's, however, nothing resembling today's Internet existed until the early 1980s. Although the term "internet" was in use as early as 1982, there was no single protocol for exchanging information on the network. The Network Control Protocol operated alongside the nascent Internet Protocol (IP).

The ARPANET/Internet technical community decided to switch to IP as the single protocol. At the time of the switchover, there were only 213 host computers connected to the Internet. Twenty years later, considering all the PCs and wireless phones connected to the Internet worldwide, good numbers are hard to come by; conceivably the host count exceeds one million times the 1983 number!

Even though "only" 213 computers were on the network, thousands of people and major institutions relied on the network, and there was great concern for the transition to succeed. IP co-inventors Robert Kahn and Vinton Cerf (et al.) described the fears: "This was a ‘flag-day' style transition, requiring all hosts to convert simultaneously or be left having to communicate via rather ad-hoc mechanisms. This transition was carefully planned within the community over several years before it actually took place and went surprisingly smoothly (but resulted in a distribution of buttons saying ‘I survived the TCP/IP transition')."

It was by no means inevitable that IP and its companion protocol, TCP, would become the overwhelmingly dominant way to move information within a building or across the globe. In the 1970s and 1980s, multiple technologies aspired to connect computers into networks. For instance, a national network of universities, BITNET, was born in 1981; it used IBM mainframe networking protocols. By the mid 1980s a business card of a university staff member had special cachet if it listed both BITNET and Internet e-mail addresses. After the PC was born, local area networks evolved, and with them local networking technologies such as Novell. And, the world had not yet settled on a single wired media standard; for instance, IBM's Token Ring competed with today's dominant Ethernet.

Only a short 10 years after the IP transition, the world was about to observe the birth of the World Wide Web. Without the underpinnings of the global peer-to-peer network that was the Internet, the Web might have appeared years later.

Joseph Hardin headed the Software Development Group (SDG) at the National Center for Supercomputing Applications (NCSA) at the University of Illinois during the heady days when the first popular Web browser, NCSA Mosaic, was developed. Asked to comment on the anniversary, Hardin remarked: "Few 20-year-olds have the distinction of having changed the world, and few 20-year-olds are, by their own reckoning, centenarians. The Internet is both young and old, and yet only at the beginning of a life that is continuously transforming ours. As we were building the net, and then the Web, we all felt this was going to be something Revolutionary—we just didn't realize it would be a permanent revolution."

The history of the Internet comprises many milestones and subtleties. Two truths stand out:

• Every inventor of important Internet technologies truly "stood on the shoulders of giants."
• At each milestone in Internet history, our vision of where things go next is poor. Few understood the Web's importance in January 1993; few predicted Napster or KaZaA in 1995; no one in 1983 expected the global Internet of 2003..

Today, a child of age 8 or less will grow up having never known a world without the Web. Millions of that child's elders assume the Internet and the Web as a part of everyday life. Where will the revolution take us in the next 20 years?

An excellent collection of historical papers and timelines is hosted by the Internet Society at: http://www.isoc.org/internet/history.

A timeline produced by PBS depicts major milestones: http://www.pbs.org/internet/timeline/index.html.

Robert H. Zakon offers a more inclusive timeline: http://www.zakon.org/robert/internet/timeline.

The transition plan describing the migration to an all-IP Internet was written by Jon Postel and labeled RFC 801: http://www.faqs.org/rfcs/rfc801.html.

This interview with Web co-inventor Robert Cailliau details how technologies such as the Next workstation and Apple's HyperCard played important roles in inspiring the Web: http://www.computer.org/internet/v2n1/cailliau.htm.