While a graduate classmate of Larry Roberts at MIT in the late ’50s and early ’60s, Len Kleinrock wrote the first papers on the underlying principles of what later came to be known as packet switching-the idea that data could be chopped up, sent over wires by various routes, and be reassembled at their destination-a central technology of today’s Internet. The parceled data was sometimes called “data blocks,” a term later dropped in favor of “packets,” coined by British networking pioneer, Donald Davies. Having joined the faculty of UCLA in 1963, Kleinrock was on the team that laid out the original specification for the Arpanet four years later. He also helped develop the interface between the Sigma-7 host computer and the first IMP, unpacked at UCLA on Labor Day weekend 1969, and oversaw transmission of the first host-to-host message, on Oct. 29. Kleinrock established and ran the Network Measurement Center, which ran experiments to test the behavior and outer limits of the network. He is still on the faculty at UCLA and is leading research and development at nomadic computing technology provider, Nomadix.

Bob Kahn, 60

At Bolt Beranek and Newman (BBN, now GTE Internetworking), the Cambridge, Mass., contractor that built much of the Arpanet’s equipment, Bob Kahn helped design and construct the IMPs. He organized the first public demonstration of the Arpanet in Washington, D.C., in October 1972. That same year, he was made director of IPTO. Kahn is co-inventor (with Vint Cerf) of TCP/IP, the lingua franca of today’s Web. Kahn also pioneered development of radio and satellite packet data networks to link computers wirelessly. After 13 years with ARPA, Kahn founded the nonprofit Corporation for National Research Initiatives in Reston, Va., to provide leadership and funding for research and development of the National Information Infrastructure. He is CNRI’s CEO and he served on the Presidents Advisory Council on the National Information Infrastructure.

Douglas Engelbart, 74

What didn’t Douglas Engelbart invent? Engelbart pioneered the mouse, hyperlinks, windows, and a score of other essentials. When Bob Taylor announced plans to build the Arpanet in 1967, Engelbart was thrilled. He volunteered to start the online Network Information Center (NIC), which would track all the network’s resources. As a result, his SDS-940 computer in the Augmentation Research Center at SRI was chosen to be the second host in the Arpanet. Engelbart developed NLS (for online systems) for storing and retrieving electronic documents. Later, in 1977, Cupertino, Calif.-based Tymshare bought the rights to NLS and renamed it Augment. Engelbart followed his progeny. In 1984, Tymshare was in turn bought by McDonnell Douglas. After retiring from the aerospace company in 1989, Engelbart founded the Bootstrap Institute, dedicated to improving the performance of organizations. He lives in the San Francisco Bay Area and continues as head of the Fremont, Calif.-based Institute.

Frank Heart, 70

A computer systems engineer, Frank Heart managed the team, which came to be known as “the IMP guys,” that designed and built the IMP subnetwork computers at BBN. Also on the IMP guys team were Ben Barker, Bernie Cosell, Will Crowther, Jim Geisman, Bob Kahn, Severo Ornstein, Hawley Rising, Truett Thach, Marty Thrope, and Dave Walden. Heart remained with BBN until his retirement, working largely in biomedical, network technology, physical sciences, and logistics computing. When he retired in 1994, he was president of BBN’s systems and technology division. The secret to Arpanet’s success, Heart says, was that “Despite the fact that it was supported by the Department of Defense, it was entirely unclassified. People could just get on and try it.”

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