ARPANET (Advanced Research Projects Agency Network) was the first operational packet-switched network and the direct precursor to the modern Internet. Funded by the U.S. Department of Defense’s ARPA (later DARPA), it pioneered the technologies and protocols that would eventually connect billions of devices worldwide.
Origins
In the 1960s, computers were expensive standalone machines. Researchers at different universities needed to share computing resources, but there was no way to connect distant computers. The idea of a computer network emerged from multiple sources, including J.C.R. Licklider’s vision of an “Intergalactic Computer Network” and Paul Baran’s work on survivable communications for the military[1].
ARPA program manager Larry Roberts led the effort to build this network, bringing together researchers from across the country.
The First Nodes
On October 29, 1969, the first ARPANET message was sent from UCLA to Stanford Research Institute[2]. The system crashed after transmitting just two letters—“LO” (attempting to type “LOGIN”)—but the concept was proven. By the end of 1969, four nodes were connected: UCLA, Stanford Research Institute, UC Santa Barbara, and the University of Utah.
Packet Switching
ARPANET’s key innovation was packet switching—breaking data into small packets that could travel independently through the network and reassemble at the destination. This was fundamentally different from the circuit-switched telephone network, where a dedicated line connected two parties. Packet switching made efficient use of network resources and was inherently resilient to failures.
Growth and Innovation
Throughout the 1970s, ARPANET grew steadily. Key developments included:
- 1971: Email was invented by Ray Tomlinson, quickly becoming the network’s most popular application
- 1973: The network went international, connecting to nodes in the UK and Norway
- 1974: Vint Cerf and Bob Kahn published the TCP/IP protocol, designed to connect different networks together
- 1983: ARPANET switched from its original NCP protocol to TCP/IP, marking the birth of the Internet as we know it
Legacy
ARPANET was officially decommissioned in 1990, but by then its successor—the Internet—was well established. ARPANET proved that geographically distributed computers could be connected into a useful network. It pioneered packet switching, developed the protocols that evolved into TCP/IP, and created the first networked community of researchers who communicated via email and shared resources.
Every time you send an email, browse a website, or stream a video, you’re using technologies that trace directly back to ARPANET.
Sources
- Hafner, Katie; Lyon, Matthew. “Where Wizards Stay Up Late: The Origins of the Internet.” Simon & Schuster, 1996.
- UCLA. “First ARPANET transmission.” Kleinrock Center for Internet Studies.