interface message processor (IMP)
At a 1967 Ann Arbor computer conference where Larry Roberts presented his intial plans for the ARPAnet to memebers of the Intergalactic Network, Wes Clark, suggested to Roberts that instead of adding networking capabilities to each of the host computers at the varied sites, they could build separate dedicated computers to route information between hosts and the network. Roberts sent out a memorandum describing Clark's idea, calling the computers "interface message processors".
BBN made a furious effort to win the contract from Larry Roberts's ARPAnet IMP RFP. In the month allotted, they spent $100,000 constructing a two-hundred-page document that was closer to finished blueprints and software design than to a proposal. Senator Ted Kennedy sent BBN a congratulatory note for winning the "interfaith message processor" contract at the end of 1968.
The BBN engineer Frank Heart led the team of IMP Guys rebuilding a military-hardened, nine-hundred-pound Honeywell 516. Severo Ornstein, a close friend of Wes Clark from their days at Lincoln Lab, was the lead hardware engineer. Bob Kahn, an MIT professor whose theoretical mindset was in every way the opposite of Heart's unyielding practicality, understood information theory innately. The software designers, including Dave Walden (the lead programmer), Will Crowther, and Bernie Cosell, were some of the first real hackers.
BBN shipped the first IMP August 30, 1969 to Kleinrock's group at UCLA. Three days later, right after Labor Day, the BBN technicians and Kleinrock's grad students connected the IMP to UCLA's Sigma 7, making it the first host on the as-yet-unborn network. The Sigma 7 and the IMP began successfully communicating with each other from the very start.
BBN sent the next IMP to Engelbart's team at SRI on October 1. On October 29, the first message was sent over the nascent network. The researchers at UCLA tried to send the message "LOGIN" one character at a time. They successfully sent "LO" before the SRI host crashed. They soon were able to get the computers successfully communicating.