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The Interface Message Processor (IMP) was the packet-switching node
Node (networking)

In communication networks, a node is an active electronic device that is attached to a network, and is capable of sending, receiving, or forwarding information over a communications channel....
 used to connect computers to the original ARPANET
ARPANET

The ARPANET developed by Defense Advanced Research Projects Agency of the United States Department of Defense during the Cold War, was the world's first operational packet switching network, and the predecessor of the global Internet....
 in the late 1960s and 1970s. It was the first generation of what is known as a router
Router

A router is a Computer network device whose software and hardware are usually tailored to the tasks of routing and forwarding information. For example, on the Internet, information is directed to various paths by routers....
 today. An initial protocol was suggested in RFC 1.






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Leonard Kleinrock and Imp1
The Interface Message Processor (IMP) was the packet-switching node
Node (networking)

In communication networks, a node is an active electronic device that is attached to a network, and is capable of sending, receiving, or forwarding information over a communications channel....
 used to connect computers to the original ARPANET
ARPANET

The ARPANET developed by Defense Advanced Research Projects Agency of the United States Department of Defense during the Cold War, was the world's first operational packet switching network, and the predecessor of the global Internet....
 in the late 1960s and 1970s. It was the first generation of what is known as a router
Router

A router is a Computer network device whose software and hardware are usually tailored to the tasks of routing and forwarding information. For example, on the Internet, information is directed to various paths by routers....
 today. An initial protocol was suggested in RFC 1. To connect to the ARPANET, host computers communicated with IMPs using a special high-speed bit-serial
Serial communications

In telecommunication and computer science, serial communication is the process of sending data one bit at one time, sequentially, over a communication channel or computer bus....
 interface (defined in BBN Report 1822
BBN Report 1822

BBN Report 1822 specifies the method for connecting a host computer to an ARPANET router, called an Interface Message Processor . This connection and protocol is generally referred to as 1822, the report number....
). The IMP itself was a ruggedized
Rugged computer

A rugged computer is a computer specifically designed to reliably operate in harsh usage environments and conditions, such as strong vibrations, extreme temperatures and wet or dusty conditions....
 Honeywell
Honeywell

Honeywell is a major United States multinational corporation list of conglomerates company that produces a variety of consumer products, engineering services, and aerospace systems for a wide variety of customers, from private consumers to major corporations and governments....
 DDP-516 minicomputer
Minicomputer

A minicomputer is a class of multi-user computers that lies in the middle range of the computing spectrum, in between the largest multi-user systems and the smallest single-user systems ....
 with special-purpose interfaces and software. In later years the IMPs were made from the non-ruggedized Honeywell 316
Honeywell 316

The Honeywell 316 was a popular 16-bit minicomputer built by Honeywell starting in 1969. It is part of the Series 16 which includes the Models 116, 316, 416, 516 and 716....
.

The idea of the IMP being a separate computer was suggested by Wes Clark
Wesley A. Clark

Wesley Allison Clark is a computer scientist and one of the main participants, along with Charles Molnar, in the creation of the LINC laboratory computer, which was the first mini-computer and shares with a number of other computers the claim to be the inspiration for the personal computer....
 to Larry Roberts
Lawrence Roberts (scientist)

Lawrence G. Roberts received the Draper Prize in 2001 "for the development of the Internet" along with Leonard Kleinrock, Bob Kahn, and Vinton Cerf....
 who led the ARPANET implementation for the Department of Defense's Advanced Research Projects Agency (ARPA). The IMP was implemented by Bolt Beranek and Newman
BBN Technologies

BBN Technologies is a high-technology company which provides research and development services. BBN is based next to Fresh Pond, Cambridge, Massachusetts in Cambridge, Massachusetts, Massachusetts, United States....
 (BBN).

The original IMP team at BBN consisted of:

  • Team Leader: Frank Heart
  • Software: Willy Crowther
    William Crowther

    William Crowther is a computer programmer and Caving. He is best known as the co-creator of Colossal Cave Adventure, a seminal computer game that influenced the first decade of computer game designer and created a new game genres, text adventures....
    , Bob Kahn
    Bob Kahn

    Robert Elliot Kahn, invented the Transmission Control Protocol , and along with Vinton G. Cerf created the Internet Protocol , the technologies used to transmit information on the Internet....
    , Dave Walden, Bernie Cosell, Hawley Rising
  • Hardware: Severo Ornstein
    Severo Ornstein

    Severo M. Ornstein is a retired computer scientist. In 1955 he joined MIT's Lincoln Laboratory as a programmer and designer for the SAGE air-defense system....
    , Ben Barker, Marty Thrope
  • Unknown: Jim Geisman, Truett Thach, Bill Bertell (Honeywell)


The first IMP delivered was to Leonard Kleinrock
Leonard Kleinrock

Leonard Kleinrock, Ph.D. is a computer scientist, and a professor of computer science at UCLA's Henry Samueli School of Engineering and Applied Science, who made several important contributions to the field of computer networking, in particular to the theoretical side of computer networking....
's group at UCLA on August 30, 1969. It was attached to a SDS Sigma-7. IMP number two was delivered to Douglas Engelbart
Douglas Engelbart

Dr. Douglas C. Engelbart is an United States inventor and early computer pioneer of German, Swedish ethnic group and Norwegian people descent....
's group at the Stanford Research Institute (SRI) on October 1, 1969. It was attached to an SDS-940
SDS 940

The SDS 940 was Scientific Data Systems' first machine designed to support time sharing directly, and was based on the SDS 930's 24-bit CPU built primarily of integrated circuits....
. The first communication between these computers connected to IMPs was the first three letters of the word "login." The SRI machine crashed after the 'g' was transmitted. A few minutes later the bug was fixed and they successfully logged in.

There was also a variant called the TIP which connected terminals instead of computers to the network, which was based on the 316. Initially, some Honeywell based IMPs were replaced with multiprocessing BBN Pluribus
Pluribus

The Pluribus multiprocessor was an early multi-processor computer designed by BBN for use as a packet switch in the ARPANET. Its design later influenced the BBN Butterfly computer....
 IMPs, but ultimately BBN developed a microprogrammed clone of the Honeywell processor.

IMPs were at the heart of the ARPANET until it was decommissioned 20 years later in 1989. The last IMP on the ARPANET was the one at the University of Maryland.

External links

  • Internet STD 39, also known as BBN Report 1822
    BBN Report 1822

    BBN Report 1822 specifies the method for connecting a host computer to an ARPANET router, called an Interface Message Processor . This connection and protocol is generally referred to as 1822, the report number....
    , "Specification for the Interconnection of a Host and an IMP".