What is ARPANET?

The U.S. Advanced Research Projects Agency Network (ARPANET) was the first public packet-switched computer network. It was first used in 1969 and finally decommissioned in 1989. ARPANET's main use was for academic and research purposes.

Many of the protocols used by computer networks today were developed for ARPANET, and it is considered the forerunner of the modern internet.

Developments leading to ARPANET

ARPANET and the subsequent computer networks leading to the internet were not the product of a single individual or organization, nor were they formed at one time. Instead, the ideas and initial research work of many people over years of time was used to form the basis of ARPANET and to build it to become the forerunner of the internet.

In the 1960s, computers were large mainframe systems. They were very expensive and were only owned by large companies, universities and governments. Users would sit at dedicated terminals, such as teletype machines, and run programs on the connected mainframe. Connections between computers was done over dedicated links. These systems were highly centralized and fault-prone.

This was during the height of the Cold War. The U.S. military was interested in creating computer networks that could continue to function after having portions removed, such as in the case of a nuclear strike. Similarly, universities were looking to develop a network that could be fault-tolerant over unreliable connections and could be used to share data and computing resources between users at different locations.

In the early 1960s, Paul Baran, working for the U.S. think tank Rand Corporation, developed the concept of distributed adaptive message block switching. This would enable small groups of data to be sent along differing paths to the destination. This idea eventually became packet communication that underlies almost all data communication today. At that time, though, it was not implemented.

Joseph C.R. Licklider became the director of ARPA's Information Processing Techniques Office (IPTO) in 1962. He was a major proponent of human-computer interaction and using computers to help people make better decisions. His influence lead ARPA to develop its network and other innovations, such as graphical user interfaces.

In 1966, Robert (Bob) Taylor became the director of IPTO. He credits the idea of ARPANET to the fact that he had three different computer terminals connected to three mainframe computers in his office that he would need to move between. This led to the obvious question: Why can't one terminal be used for any computer?

History of ARPANET

Development of ARPANET began in 1966. Several standards were developed. Network Control Program (NCP) would handle communication between hosts and could support the first commands, Telnet and File Transfer Protocol (FTP). It would use packet-switching technology to communicate. Interface Message Processor was developed to pass messages between hosts. This can be considered the first packet gateway or router. Hardware Modems were designed and sent out to the participating organizations.

The first message sent over ARPANET happened on Oct. 29, 1969. Charley Kline, who was a student at the University of California Los Angeles (UCLA), tried to log in to the mainframe at the Stanford Research Institute (SRI). He successfully typed in the characters L and O, but the computer crashed when he typed the G of the command LOGIN. They were able to overcome the initial crash, however, and had a successful connection that same day.

The first permanent connection between UCLA and SRI was put into place on Nov. 21, 1969. Two more universities joined ARPANET as founding members on Dec. 5, 1969. These were the University of California, Santa Barbara and University of Utah School of Computing.

ARPANET grew rapidly in the early 1970s. Many universities and government computers joined the network during this time. In 1975, ARPANET was declared operational and was used to develop further communications technology. In time, several computers in other countries were also added using satellite links.

Many packet-based networks quickly came into operation after ARPANET became popular. These various networks could not communicate with one another due to the requirements of standardized equipment in the existing networks. Therefore, TCP/IP was developed as a protocol to enable communication between different networks. It was first put into operation in 1977.

TCP/IP enabled an interconnected network of networks and is the foundational technology of the internet. On Jan. 1, 1983, TCP/IP replaced NCP as the underlying packet-switching technology of ARPANET.

Also, in 1983, ARPANET was divided into two networks between military and civilian use. The word internet was first used to describe the combination of these two networks.

The importance of ARPANET diminished as other networks became more dominant in the mid-1980s. The National Science Foundation Network replaced ARPANET as the backbone of the internet in 1986. Commercial and other network providers also began operating during this time.

ARPANET was shut down in 1989. It was finally decommissioned in 1990.

Legacy of ARPANET

ARPANET stands as a major changing point in the development of computer technology. Many underlying internet technologies were first developed on or for ARPANET. Telnet and FTP protocols were some of the first used on ARPANET, and they are still in use today. TCP/IP was developed on it. The first network email was sent in 1971 over ARPANET. It also hosted what is considered the first marketing spam email in 1978.

ARPANET also led to many other networking firsts. List servers, or listservs, became early social networks. Early voice communication protocols were developed on it. Password protection and data encryption were developed for use over ARPANET.

This was last updated in November 2021

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