History of the Internet
What Was ARPANET? The Network That Started It All
Before the internet, there was ARPANET — a small research network that proved computers scattered across a continent could act as one.
Who built it and why
ARPANET was funded by the Advanced Research Projects Agency, part of the U.S. Department of Defense, and built by researchers at universities and at the firm Bolt, Beranek and Newman (BBN). Its goal was practical: let expensive, scarce computers at different institutions share resources. A researcher in California should be able to run a program on a machine in Massachusetts.
A common myth is that ARPANET was designed to survive a nuclear war. The truth is subtler: the packet-switching ideas it used were partly motivated by survivable-communications research, but ARPANET itself was a resource-sharing network for scientists.
The technology: packet switching
Traditional phone calls used circuit switching — a dedicated wire held open for the whole conversation. ARPANET used packet switching instead: data is chopped into small packets, each labeled with its destination, and each packet is passed hop by hop across the network independently. If one path is busy or broken, packets take another. This is efficient and resilient, and it remains the foundation of the internet today.
The physical switches were called Interface Message Processors (IMPs) — refrigerator-sized minicomputers that sat between each host and the network, effectively the first routers.
"LO" — the first message
On October 29, 1969, a student at UCLA tried to log in to a machine at the Stanford Research Institute. He typed "L," then "O," and the remote system crashed. So the first message sent across ARPANET was the accidental, almost poetic "LO" — as in "lo and behold." The full login worked about an hour later.
What ARPANET proved
ARPANET grew from four nodes in 1969 to dozens through the 1970s. Along the way it delivered several firsts that still shape the internet:
- Email (1971) quickly became the network's dominant use.
- The @ symbol was chosen to separate a user from their host machine.
- It demonstrated that heterogeneous computers could interoperate through shared protocols.
ARPANET was formally decommissioned in 1990, its role long since absorbed by the TCP/IP internet it had made possible. But every time you load a web page, you are using the direct descendant of that first four-node experiment.