The Interface Message Processor (IMP) was the packet-switching node used to connect computers to the original ARPANET in the late 1960s and 1970s. To connect to the ARPANET, host computers communicated with IMPs using a special high-speed bit-serial interface. The IMP itself was a Honeywell DDP-516 mini-computer with special-purpose interfaces and software.

IMPs are the ancestor of modern Internet routers.

References

• A Technical History of the ARPANET with photos of IMP
• IMP history with photo of developers
• Internet STD 39, a.k.a. Bolt, Beranek and Newman Report 1822, "Specification for the Interconnection of a Host and an IMP".

Networking hardware | ARPANET

Interface Message Processor