ARPANET Interface Message Processor
The refrigerator-sized minicomputer that connected the first four ARPANET sites in 1969, the ancestor of the internet's routers.
The Advanced Research Projects Agency funded the ARPANET to link research computers. Instead of wiring every computer to every other, each site connected to a small Interface Message Processor, or IMP, which handled the network traffic. Bolt Beranek and Newman built the IMPs from ruggedized Honeywell DDP-516 minicomputers.
The first IMP was installed at UCLA on September 2, 1969. On October 29, 1969, a student programmer at UCLA, working with a team at the Stanford Research Institute, sent the first message across the link. The system crashed after the letters 'LO' of an intended 'LOGIN', and was running again within about an hour. By the end of the year the network connected UCLA, SRI, UC Santa Barbara and the University of Utah.
Why it matters
The IMP was the first packet-switching router in a working network. The design of ARPANET led to the TCP/IP protocols and, through the 1970s and 1980s, to the internet.
Key facts
- First IMP delivered to UCLA on September 2, 1969.
- First message sent October 29, 1969.
- Built from a Honeywell DDP-516 minicomputer.
- Four sites were connected by December 1969.
Sources
- Campbell-Kelly, Martin, and William Aspray, et al. Computer: A History of the Information Machine. 3rd ed. Westview Press, 2013.
- Hafner, Katie, and Matthew Lyon. Where Wizards Stay Up Late: The Origins of the Internet. Simon & Schuster, 1996.
- Heart, Frank, et al. "The Interface Message Processor for the ARPA Computer Network." AFIPS Conference Proceedings, 1970.