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ARPANET logical map, March 1977.

ARPANET (Advanced Research Projects Agency Network), created by the Defense Advanced Research Projects Agency (DARPA) of the United States Department of Defense, was the world's first operational packet switching network, and the predecessor of the contemporary global Internet. The packet switching of the ARPANET was based on designs by Lawrence Roberts, of the Lincoln Laboratory.[1]

Packet switching, now the dominant basis for data communications worldwide, then was a new and important concept. Data communications had been based upon the idea of circuit switching, as in the old, typical telephone circuit, wherein a dedicated circuit occupied for the duration of the telephone call, and communication is possible only with the single party at the far end of the circuit.

With packet switching, a data system could use one communications link to communicate with more than one machine by disassembling data into datagrams, then gather these as packets. Thus, not only could the link be shared (much as a single post box can be used to post letters to different destinations), but each packet could be routed independently of other packets.



The earliest ideas for a computer network intended to allow general communications among computer users were formulated by the computer scientist J. C. R. Licklider, of the Bolt, Beranek and Newman (BBN) company, in August 1962, in memoranda discussing his concept for an “Intergalactic Computer Network”. Those ideas contained almost everything that composes the contemporary Internet.

In October 1963, at the US Defense Department, Licklider was appointed head of the Behavioral Sciences and Command and Control programs, at the Advanced Research Projects Agency — ARPA (the initial ARPANET acronym). He then convinced Ivan Sutherland and Bob Taylor that this computer network concept was very important, meriting development, although he left ARPANET before anyone worked on his concept.

ARPA and Bob Taylor continued their interest in creating such a computer communications network, in part, to allow ARPA-sponsored researchers at various corporate and academic locales to put to use the computers ARPA was providing them, and, in part, to make new software and other computer science results quickly and widely available. In his office, Taylor had three different computer terminals, each connected to three different computers, which ARPA was funding: the first, for the System Development Corporation (SDC) Q-32, in Santa Monica; the second, for Project Genie, at the University of California, Berkeley; and the third, for Multics, at MIT; Taylor recalls the circumstance:

For each of these three terminals, I had three different sets of user commands. So, if I was talking online with someone at S.D.C., and I wanted to talk to someone I knew at Berkeley, or M.I.T., about this, I had to get up from the S.D.C. terminal, go over and log into the other terminal and get in touch with them. I said, “Oh Man!”, it’s obvious what to do: If you have these three terminals, there ought to be one terminal that goes anywhere you want to go. That idea is the ARPANET.[2]

Somewhat contemporaneously, several other people had (mostly independently) worked out the aspects of “packet switching”, with the first public demonstration presented by the National Physical Laboratory (NPL), on 5 August 1968, in the United Kingdom .[3]


By mid-1968, Taylor had prepared a complete plan for a computer network, and, after ARPA’s approval, a Request For Quotation (RFQ) was sent to 140 potential bidders. Most computer science companies regarded the ARPA–Taylor proposal as outlandish, and only twelve submitted bids to build the network; of the twelve, ARPA regarded only four as top-rank contractors. At year’s end, ARPA considered only two contractors, and awarded the contract to build the network to BBN Technologies on 7 April 1969.

The initial, seven-man BBN team were much aided by the technical specificity of their response to the ARPA RFQ — and thus quickly produced the first working computers. The BBN-proposed network closely followed Taylor’s ARPA plan: a network composed of small IMP computers, Interface Message Processors (contemporary routers). At each site, the IMPs performed store-and-forward packet switching functions, and were interconnected with modems that were connected to leased lines (initially running at 50 kbit/second). The host computers were connected to the IMPs via custom serial interfaces connecting to the ARPANET. The system, including the hardware and the packet switching software, was designed and installed in nine months.

To build the first-generation IMPs, BBN Technologies initially used a rugged computer version of the Honeywell DDP-516 computer (originally) configured with 24 kB of (expandable) core memory, and a 16-channel Direct Multiplex Control (DMC) direct memory access control unit.[4] The DMC established custom interfaces with each of the host computers and modems. In addition to the front-panel lamps, the DDP-516 computer also features a special set of 24 indicator-lamps showing the status of the IMP communication channels. Each IMP could support up to four local hosts, and could communicate with up to six remote IMPs via leased lines.

ARPA deployed

Historical document: First ARPANET IMP log: the first message ever sent via the ARPANET, 10:30 PM, 29 October 1969. This IMP Log excerpt, kept at UCLA, describes setting up a message transmission from the UCLA SDS Sigma 7 Host computer to the SRI SDS 940 Host computer.

The initial ARPANET consisted of four IMPs installed at:

  1. UCLA, where Leonard Kleinrock had established a Network Measurement Center (with an SDS Sigma 7 being the first computer attached to it).
  2. The Stanford Research Institute's Augmentation Research Center, where Douglas Engelbart had created the ground-breaking NLS system, a very important early hypertext system (with the SDS 940 that ran NLS, named 'Genie', being the first host attached).
  3. UC Santa Barbara (with the Culler-Fried Interactive Mathematics Centre's IBM 360/75, running OS/MVT being the machine attached).
  4. The University of Utah's Computer Science Department, where Ivan Sutherland had moved (for a DEC PDP-10 running TENEX).

The first message transmitted over the ARPANET was sent by UCLA student programmer Charley Kline, at 10:30 PM, on 29 October 1969. Supervised by Prof. Leonard Kleinrock, Kline transmitted from the university’s SDS Sigma 7 Host computer to the Stanford Research Institute’s SDS 940 Host computer. The message text was the word “login”; the “l” and the “o” letters were transmitted, but the system then crashed. Hence, the literal first message over the ARPANET was “lo”. About an hour later, having recovered from the crash, the SDS Sigma 7 computer effected a full “login”. The first permanent ARPANET link was established on 21 November 1969, between the IMP at UCLA and the IMP at the Stanford Research Institute. By 5 December 1969, the entire 4-node network was connected.[5]

The contents of the first e-mail transmission (1971) have been forgotten; in the FAQ of his website, the sender, Ray Tomlinson (who sent the message between two computers sitting side-by-side) claims that the contents were “entirely forgettable, and I have, therefore, forgotten them”, and speculates that the message likely was “QWERTYUIOP” or some such.[6]

Software & protocols

The starting point for host-to-host communication on the ARPANET was the 1822 protocol, which defined how a host computer transmitted messages to an ARPANET IMP. The message format was designed to work unambiguously with a broad range of computer architectures. An 1822 message essentially consisted of (i) a message type, (ii) a numeric host address, and (iii) a data field. To send a data message to another host, the transmitting host would format a data message containing the destination host's address and the data message being sent, and then transmit the message through the 1822 hardware interface. The IMP then delivered the message to its destination address, either by delivering it to a locally connected host, or by delivering it to another IMP. When the message was ultimately delivered to the destination host, the receiving IMP would transmit a Ready for Next Message (RFNM) acknowledgement to the sending, host IMP.

Unlike modern Internet datagrams, the ARPANET was designed to reliably transmit 1822 messages, and to inform the host computer when it loses a message; the contemporary IP is unreliable, whereas the TCP is reliable. Nonetheless, the 1822 protocol proved inadequate for handling multiple connections among different applications residing in a host computer. This problem was addressed with the Network Control Program (NCP), which provided a standard method to establish reliable, flow-controlled, bidirectional communications links among different processes in different host computers. The NCP interface allowed application software to connect across the ARPANET by implementing higher-level communication protocols, an early example of the protocol layering concept incorporated to the OSI model. In 1983, TCP/IP protocols replaced NCP as the ARPANET’s principal protocol, and the ARPANET then became one component of the early Internet.

Network Applications

NCP provided a standard set of network services that could be shared by several applications running on a single host computer. This led to the evolution of application protocols that operated, more or less, independently of the underlying network service. When the ARPANET migrated to the Internet protocols in 1983, the major application protocols migrated with it.

  • E-mail: In 1971, Ray Tomlinson, of the BBN company sent the first network e-mail.[7] By 1973, e-mail constituted 75 per cent of ARPANET traffic.
  • File transfer: By 1973, the File Transfer Protocol (FTP) specification had been defined and implemented, enabling file transfers over the ARPANET.


In March, 1970, the ARPANET reached the East Coast of the United States, when a BBN company IMP was connected to the network. Thereafter, the ARPANET grew: 9 IMPs by June 1970 and 13 IMPs by December 1970, then 18 by September 1971 (when the network included 23 university and government hosts); 29 IMPs by August 1972, and 40 by September, 1973. By June 1974, there were 46 IMPs, and in July 1975, the network numbered 57 IMPs. By 1981, the number was 213 host computers, with another host connecting approximately every twenty days.

In 1968, two satellite links, traversing the Pacific and Atlantic oceans, to Hawaii and Norway, one, the Norwegian Seismic Array (NORSAR), were connected to the ARPANET. Moreover, from Norway, a terrestrial circuit added a London IMP to the network in 1973.

Given that its primary function was funding research and development, the ARPA, in 1975, transferred ARPANET control to the Defense Communications Agency, a component of the US Defense Department. In 1983, the US military sub-networks of the ARPANET became the discrete Military Network (MILNET) for unclassified defense department communications; separating the civil and military networks reduced the 113-node ARPANET by 68 nodes.

Development: hardware

Support for inter-IMP circuits of up to 230.4 kbit/s was added in 1970, although considerations of cost and IMP processing power meant this capability was not actively used.

1971 saw the start of the use of the non-ruggedized (and therefore significantly lighter) Honeywell 316 as an IMP. It could also be configured as a Terminal IMP (TIP), which added support for up to 63 ASCII serial terminals through a multi-line controller in place of one of the hosts. The 316 featured a greater degree of integration than the 516, which made it less expensive and easier to maintain. The 316 was configured with 40 kB of core memory for a TIP. The size of core memory was later increased, to 32 kB for the IMPs, and 56 kB for TIPs, in 1973.

In 1975, BBN introduced IMP software running on the Pluribus multi-processor. These appeared in a small number of sites. In 1981, BBN introduced IMP software running on its own C/30 processor product.

The original IMPs and TIPs were phased out as the ARPANET was shut down after the introduction of the NSFNet, but some IMPs remained in service as late as 1989.

Senator Albert Gore began to craft the High Performance Computing and Communication Act of 1991 (commonly referred to as "The Gore Bill") after hearing the 1988 report toward a National Research Network submitted to Congress by a group chaired by UCLA professor of computer science, Leonard Kleinrock, one of the central creators of the ARPANET (the ARPANET, first deployed by Kleinrock and others in 1969, is the predecessor of the Internet). The bill was passed on December 9, 1991 and led to the National Information Infrastructure (NII) which Gore referred to as the "information superhighway."

The ARPANET under nuclear attack

A common ARPANET semi-myth posits that the computer network was designed to survive a nuclear attack. In A Brief History of the Internet, the Internet Society describe the coalescing of the technical ideas that produced the ARPANET:

It was from the RAND study that the false rumor started, claiming that the ARPANET was somehow related to building a network resistant to nuclear war. This was never true of the ARPANET, only the unrelated RAND study on secure voice considered nuclear war. However, the later work on Internetting did emphasize robustness and survivability, including the capability to withstand losses of large portions of the underlying networks.[8]

Although the ARPANET was designed to survive subordinate-network losses, the principal reason was that the switching nodes and network links were unreliable, even without any nuclear attacks. About the resources scarcity that spurred the creation of the ARPANET, Charles Herzfeld, ARPA Director (1965–67), said:

The ARPANET was not started to create a Command and Control System that would survive a nuclear attack, as many now claim. To build such a system was, clearly, a major military need, but it was not ARPA’s mission to do this; in fact, we would have been severely criticized had we tried. Rather, the ARPANET came out of our frustration that there were only a limited number of large, powerful research computers in the country, and that many research investigators, who should have access to them, were geographically separated from them.[9]


The support and management of ARPA contributed to the successful creation of the ARPANET. To wit, the ARPANET Completion Report, jointly published by the BBN company and ARPA, concludes that:

. . . it is somewhat fitting to end on the note that the ARPANET program has had a strong and direct feedback into the support and strength of computer science, from which the network, itself, sprung. Template:NamedRef

The ARPANET in film and other media

  • A 1969 movie called 'The Computer Wore Tennis Shoes.
  • A 1983 movie, WarGames, is a story of possible nuclear warfare averted by an intelligent but anxious teen who hacks into a government command and control system, the WOPR (a reference to the actual military WMCCS).
  • A 1985 episode of the U.S. television sitcom Benson includes a scene in which ARPANET is accessed. This is believed to be the first incidence of a popular TV show referencing the Internet or its progenitors.
  • In Let the Great World Spin: A Novel, published in 2009 but set in 1974 and written by Colum McCann, a character named The Kid and others use ARPANET from a Palo Alto computer to dial phone booths in New York City in order to hear descriptions of Philippe Petit's tight rope walk between the World Trade Center Towers.
  • There is an electronic music artist known as Arpanet, Gerald Donald, one of the members of Drexciya. The name is formatted as a word instead of an acronym, but is still a clear nod to ARPANET. The artist's 2002 album Wireless Internet features commentary on the expansion of the internet via wireless communication, with songs such as NTT DoCoMo, dedicated to the mobile communications giant based in Japan.

See also



Further reading

  • Arthur Norberg, Judy E. O'Neill, Transforming Computer Technology: Information Processing for the Pentagon, 1962-1982 (Johns Hopkins University, 1996) pp. 153-196
  • A History of the ARPANET: The First Decade (Bolt, Beranek and Newman, 1981)
  • Katie Hafner and Matthew Lyon, Where Wizards Stay Up Late: The Origins of the Internet (Simon and Schuster, 1996) ISBN 0743468376
  • Janet Abbate, Inventing the Internet (MIT Press, Cambridge, 1999) pp. 36-111
  • Michael A. Banks On the Way to the Web: The Secret History of the Internet and Its Founders (APress/Springer Verlag, 2008) ISBN 1430208694
  • Peter H. Salus, Casting the Net: from ARPANET to Internet and Beyond (Addison-Wesley, 1995)
  • M. Mitchell Waldrop, The Dream Machine: J. C. R. Licklider and the Revolution That Made Computing Personal (Viking, New York, 2001)

Detailed technical reference works

External links

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