Forty years ago—on December 5, 1969—the U.S. Department of Defense's Advanced Research Projects Agency (ARPA) connected four computer network nodes at the University of California, Los Angeles, (U.C.L.A.), the Stanford Research Institute (S.R.I.) in Menlo Park, Calif., U.C. Santa Barbara (UCSB), and the University of Utah. The "Sigma 7" note next to the circle depicting the UCLA node refers to the Sigma 7 computer at UCLA's Network Measurement Center that Vint Cerf connected to ARPANET.