In 1969 , at UCLA Network Measurement Center, the first Interface Message Processor (IMP) was connected to its SDS Sigma-7 mainframe.
This established the first node of what became the ARPANET, the first wide-area packet switching network. Acoustics consulting firm Bolt, Beranek and Newman (BBN) designed four Interface Message Processors (IMPs), machines that would create open communication between four different computers running on four different operating systems.
Learn more at http://computer.howstuffworks.com/arpanet.htm.
