- In full:
- Advanced Research Projects Agency Network
ARPANET
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What was ARPANET?
The ARPANET (Advanced Research Projects Agency Network) was an experimental computer network and a precursor to the Internet. It was funded by the U.S. Defense Department's Advanced Research Projects Agency (ARPA) in the late 1960s to link computers at Pentagon-funded research institutions via telephone lines.
Initially, military commanders sought a communication system without a central core that could be destroyed in an attack. While ARPANET's purpose was more academic, its structure resembled the military's vision as more academic facilities joined the network. ARPANET was transferred to the Defense Communications Agency in 1975 and was shut down in 1989.
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Why did the United States government create ARPANET?
The United States government created ARPANET, or the Advanced Research Projects Agency Network, through the U.S. Defense Department's ARPA in the late 1960s.
Amidst the Cold War, military officials sought a decentralized computer communications system that lacked a central core vulnerable to enemy attack. While ARPANET's primary purpose was academic, its structure mirrored the military's vision of a network without a central headquarters.
In 1983, ARPANET was divided into MILNET for military use and a civilian version, with the term "Internet" initially referring to the combination of these networks.
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How did ARPANET connect computers together?
ARPANET connected computers using packet switching, a novel approach where messages were divided into small packets that traveled independently across various circuits to their destination, where they were reassembled. This method differed from traditional systems that required a dedicated connection between each pair of users.
Paul Baran conceived the idea of packet switching, also known as "hot-potato routing," to ensure continuous computer communication even during a nuclear attack. Although the military initially ignored it, ARPA rediscovered Baran's concept, making ARPANET feasible.
In late 1969, UCLA sent the first packet-switched message to the Stanford Research Institute. By 1971, the network expanded to 15 nodes and 23 host terminals, connecting universities, contractors, and organizations like NASA.
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What was packet switching, and why was it important for ARPANET?
Packet switching is a digital network method where data files are divided into smaller units called "packets" that are transmitted through nodes or "switches". These switches route the packets to their destination, where they are reassembled.
ARPANET arose from the desire to share information over great distances without dedicated phone connections between computers on a network, which required packet switching. Paul Baran, a researcher at RAND Corporation, developed the idea of packet switching, also known as "hot-potato routing," for a computer communications network that could survive a nuclear attack. ARPANET was the first public packet-switched network. Packet-switched communication is perhaps the most important legacy handed down to the Internet by ARPANET.
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Who were some of the key people or organizations involved in building ARPANET?
Key individuals and organizations were instrumental in building ARPANET, the precursor to the Internet, under the funding of the U.S. Defense Department's Advanced Research Projects Agency (ARPA).
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J.C.R. Licklider, as the director of ARPA's Information Processing Techniques Office (IPTO), emphasized interactive computing and the belief that humans and computers could improve the world. His work led to ARPA's pivotal role in the development of computer networks.
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Robert Taylor, another IPTO director, secured funding for ARPANET, recognizing the inefficiency of using multiple terminals for different computer systems. He and Licklider co-authored "The Computer as a Communication Device," which highlighted the potential of networked digital computing.
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Lawrence Roberts supervised ARPANET's construction and presented the network's technical specifications in 1967. He later incorporated Wesley Clark's idea of using smaller computers called interface message processors (IMPs) for networking.
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Leonard Kleinrock and his student Charley Kline sent the first message over ARPANET in 1969, marking a significant milestone in computer communication.
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Bolt, Beranek, and Newman (BBN) won the contract to build the ARPANET in 1969.
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Vinton Cerf and Bob Kahn developed the transmission-control protocol/Internet protocol (TCP/IP), which allowed different networks to exchange data, a crucial innovation for the Internet's development.
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How did ARPANET influence the development of the modern Internet?
ARPANET, funded by the U.S. Defense Department, was an experimental computer network that served as the forerunner to the Internet. It was created in the late 1960s to link computers at Pentagon-funded research institutions via telephone lines.
ARPANET's purpose was more academic than military, but it took on a tentacle-like structure that military officials had envisioned. During its first 10 years, ARPANET was a test bed for networking innovations and new applications and protocols. In 1977, the transmission-control protocol/Internet protocol (TCP/IP) was first tested on ARPANET. TCP/IP allowed one network to hand off data packets to another, then another, and another, which remains the basis of the modern Internet.
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ARPANET, experimental computer network that was the forerunner of the Internet. The Advanced Research Projects Agency (ARPA), an arm of the U.S. Defense Department, funded the development of the Advanced Research Projects Agency Network (ARPANET) in the late 1960s. Its initial purpose was to link computers at Pentagon-funded research institutions over telephone lines.
At the height of the Cold War, military commanders were seeking a computer communications system without a central core, with no headquarters or base of operations that could be attacked and destroyed by enemies thus blacking out the entire network in one fell swoop. ARPANET’s purpose was always more academic than military, but, as more academic facilities connected to it, the network did take on the tentacle-like structure military officials had envisioned. The Internet essentially retains that form, although on a much larger scale.
Roots of a network
ARPANET was an end-product of a decade of computer-communications developments spurred by military concerns that the Soviets might use their jet bombers to launch surprise nuclear attacks against the United States. By the 1960s, a system called SAGE (Semi-Automatic Ground Environment) had already been built and was using computers to track incoming enemy aircraft and to coordinate military response. The system included 23 “direction centers,” each with a massive mainframe computer that could track 400 planes, distinguishing friendly aircraft from enemy bombers. The system required six years and $61 billion to implement.
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The system’s name hints at its importance, as author John Naughton points out. The system was only “semi-automatic,” so human interaction was pivotal. For Joseph Carl Robnett Licklider, who would become the first director of ARPA’s Information Processing Techniques Office (IPTO), the SAGE network demonstrated above all else the enormous power of interactive computing—or, as he referred to it in a seminal 1960 essay, of “man-computer symbiosis.” In his essay, one of the most important in the history of computing, Licklider posited the then-radical belief that a marriage of the human mind with the computer would eventually result in better decision-making.
In 1962, Licklider joined ARPA. According to Naughton, his brief two-year stint at the organization seeded everything that was to follow. His tenure signaled the demilitarization of ARPA; it was Licklider who changed the name of his office from Command and Control Research to IPTO. “Lick,” as he insisted on being called, brought to the project an emphasis on interactive computing and the prevalent utopian conviction that humans teamed with computers could create a better world.
Perhaps in part because of Cold War fears, during Licklider’s IPTO tenure, it is estimated that 70 percent of all U.S. computer-science research was funded by ARPA. But many of those involved said that the agency was far from being a restrictive militaristic environment and that it gave them free rein to try out radical ideas. As a result, ARPA was the birthplace not only of computer networks and the Internet but also of computer graphics, parallel processing, computer flight simulation, and other key achievements.
Ivan Sutherland succeeded Licklider as IPTO director in 1964, and two years later Robert Taylor became IPTO director. Taylor would become a key figure in ARPANET’s development, partly because of his observational abilities. In the Pentagon’s IPTO office, Taylor had access to three teletype terminals, each hooked up to one of three remote ARPA-supported time-sharing mainframe computers—at Systems Development Corp. in Santa Monica, at UC Berkeley’s Genie Project, and at MIT’s Compatible Time-Sharing System project (later known as Multics).
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In his room at the Pentagon, Taylor’s access to time-shared systems led him to a key social observation. He could watch as computers at all three remote facilities came alive with activity, connecting local users. Time-shared computers allowed people to exchange messages and share files. Through the computers, people could learn about each other. Interactive communities formed around the machines.
Taylor also decided that it made no sense to require three teletype machines just to communicate with three incompatible computer systems. It would be much more efficient if the three were merged into one, with a single computer-language protocol that could allow any terminal to communicate with any other terminal. These insights led Taylor to propose and secure funding for ARPANET.
A plan for the network was first made available publicly in October 1967, at an Association for Computing Machinery (ACM) symposium in Gatlinburg, Tennessee. There, plans were announced for building a computer network that would link 16 ARPA-sponsored universities and research centers across the United States. In the summer of 1968, the Defense Department put out a call for competitive bids to build the network, and in January 1969 Bolt, Beranek, and Newman (BBN) of Cambridge, Massachusetts, won the $1 million contract.
According to Charles M. Herzfeld, the former director of ARPA, Taylor and his colleagues wanted to see if they could link computers and researchers together. The project’s military role was much less important. But at the time it was launched, Herzfeld noted, no one knew whether it could be done, so the program, initially funded on $1 million diverted from ballistic-missile defense, was risky.
Taylor became ARPA’s computer evangelist, picking up Licklider’s mantle and preaching the gospel of distributed interactive computing. In 1968, Taylor and Licklider co-authored a key essay, “The Computer as a Communication Device,” which was published in the popular journal Science and Technology. It began with a thunderclap: “In a few years, men will be able to communicate more effectively through a machine than face to face.” The article went on to predict everything from global online communities to mood-sensing computer interfaces. It was the first inkling the public ever had about the potential of networked digital computing, and it attracted other researchers to the cause.