Almost everyone is familiar with the internet – even those that don’t have access to it have an idea of what the global network is. But have you ever heard of Arpanet? This is what existed before the internet. Although this network ceased to exist in 1990 and has since been largely forgotten, the knowledge of how it worked and its development history enables us to gain a deeper understanding of the internet today.

Arpanet – the network’s history

The 1960s signaled the triumph of the computers. For private users, technical devices were usually out of reach due to their price. However, in the areas of scientific research and the military, working without computers already was almost unimaginable. They also became increasingly important for large and medium-sized businesses. In order to exchange information faster, many tried to connect up their networks to exchange information as quickly as possible. In the 1960s, scientists still had to send data in the form of printouts – a laborious and time-consuming process. Furthermore, the historical context must be taken into account in order to be able to place the development of the Arpanet correctly: the USA was in the middle of the Cold War with the Soviet Union.

At this time, these two nations were not only engaged in a near-limitless arms race and various proxy wars, they also tried to outdo each other when it came to science, space travel in particular. Considering the political situation at the time, it’s hardly surprising that the missions to set up a US computer network came from the military – more precisely, from the Advanced Research Projects Agency (ARPA). The president at the time, Dwight D. Eisenhower, had already founded ARPA in 1958 as an agency of the Ministry of Defense, responding to the launch of the Soviet Sputnik satellite.

In order to be able to better coordinate scientific projects and catch up to the research of the Soviet Union, this new authority had the task of organizing military research projects centrally (under the name DARPA – the authority is still active today, for your information). To this end, a project was devoted to networking computers from various university research institutions. In 1962, the computer scientist and psychologist, J.C.R. Licklider, took over the management position at ARPA. He already had a concrete idea for a network and was able to inspire the two IT pioneers, Robert Taylor and Ivan Sutherland, with his vision. From then on, the two computer scientists conducted research on a decentralized network (Licklider himself left ARPA and the project in 1964).

Initially there was no support from the Ministry of Defence, however, in 1965 the research work was very successful and was eventually completed in 1969. BBN Technologies – an IT company for which, interestingly enough, Linklider had worked as Vice President for a long time – was then commissioned to carry out the technical implementation.

On 29th October 1969, approximately three months after Buzz Aldrin and Neil Armstrong first set foot on the moon, the programmer Charley Kline was able to send the first fully readable message via ARPANET: 'login'. At this time, the newly developed network consisted of exactly four computers in four different locations: the University of California, Los Angeles (UCLA), the University of California, Santa Barbara (UCSB), the Stanford Research Institute (SRI International), and the University of Utah (UU).


Strictly speaking, the first delivery took place an hour earlier. Kline had also tried to send the word 'login', but the connection was disrupted after only L and O were written. After the error was fixed the second attempt could take place, which was then successful.

Gradually, the network was expanded and further American universities and authorities were connected with each other. In 1973, the network finally made the leap across the Atlantic and was also used in Europe. In 1983, the TCP/IP network protocol was also used for Arpanet, making the older network a part of the internet. In 1990, Arpanet was finally discontinued and replaced by the NSFNet, which had been in existence since 1985. NSFNet was discontinued in 1995.

The technology behind Arpanet

Several technical developments and information science concepts contributed to Arpanet’s creation. Some of the fundamental inventions did not come from the commissioned scientists themselves but were – in the spirit of an open, global knowledge culture – contributed by other researchers.

Decentralized network

The basic idea came from J.C.R Licklider and manifested itself in his vision of the Intergalactic Computer Network. He wanted to develop a network that worked independently of the computer’s location, the systems used and – ideally – even if the user didn’t have a lot of IT knowledge. Within networks like these, each participant should be able to communicate with each other (this applies to both the human user and the machine user). Although nodes were (and still are) necessary for this purpose, there is no central point from which data can be distributed.

This meant that the idea of an end-to-end connection (such as telephone calls), which was prevalent at that time, was abandoned: telephone calls are accepted at a central interface and then forwarded by switchboard operators, i.e. a direct line is established to the recipient.

Packet switching

Data packets are sent within the decentralized network. However, not all the information to be transmitted is put into a packet and sent on its way. It is divided into several packets instead, known as packet switching. Each packet works independently of its siblings (i.e. the other packets that transmit parts of the information). This also means that the packets can take different routes because there is no end-to-end connection. The packets are then put together once they are received. Packet switching works differently to circuit switching, which you are probably familiar with from the phone network.

The advantage of packet switching is that the network is used much more efficiently. Several participants share the same channels and send their parcels using them – on absolutely equal footing. Accordingly, the Arpanet also laid the foundation for what our society today is calling net neutrality. In addition, there’s less chance of complete network failure due to the many possible routes available.

Interface Message Processor (IMP)

In order for the different computers (based on different systems) to be able to communicate with each other, it was necessary to create interfaces to regulate communication between participants. For this purpose, they first looked for a software solution but finally decided to connect mini computers between the normal computers and the network. These interface message processors (IMPs) were smaller (in relation to computers that took up a whole room in those days) machines that provided interoperability in the network.

Built by BBN Technologies, the IMPs were based on mini computers from Honeywell. Their function would nowadays be compared to that of a router: data packets are sent via them to the correct recipients. The receiver IMP then sends a confirmation, but only if the packet arrives without errors, otherwise the sender will automatically reactivate and restart the transmission. When Arpanet first started out, it had a speed of 50 kbit per second and was implemented via telephone lines.

1822 protocol

In order for the IMPs to communicate with each other, BBN Technologies introduced a new standard: the 1822 protocol, named after BBN Report 1822, in which the company first described the protocol. In this protocol, the formalities required for communication in Arpanet were specified. Since only the intermediate mini computers had to comply with these regulations (the connection from host to IMP had to be managed by each site itself), the protocol ensured interoperability.

The protocol required the packet to contain two sections: the information (or part of it) you want to transmit and a header. This header section also contains a numeric recipient address (comparable to the IP address) with which the sender IMP can determine the receiver IMP so that the packets arrive at the correct location. Packets had a maximum size of 8159 bits, 96 of which were reserved for the header.

Network Control Program (NCP)

The Network Control Program (NCP) is also a protocol, however, it’s used in the middle level (transport layer) of communication. This is higher than the 1822 protocol, which can be located on the three lowest levels of the network architecture: physical layer, data link layer, & network layer. The main tasks of the NCP are to establish, terminate, or redirect connections between two hosts. In order to be able to establish a connection at any time, a so-called logger was integrated into the protocol. This service was busy searching for login attempts from other host computers.


The OSI model for layer architecture of network protocols used today didn’t exist at the beginning of Arpanet. The seven-layer reference model was only introduced in 1983. Nevertheless, the protocols of Arpanet can also be roughly classified in this model.

The Network Control program was replaced on 1st January 1983 by the successor TCP/IP (the same family of network protocols on which the internet is still based). This day of switching known as Flag Day was comparatively complex since the different protocols cannot be used side by side. It isn’t possible for hosts using NCP to communicate with hosts using TCP/IP. It was, therefore, necessary to start the complete network on the cut-off date.


Although the Unix operating system is not directly connected to Arpanet, the development of both technologies ran parallel. Both Unix and the programming language C, which the operating level is based on, influenced the development of Arpanet. The software could already be used on many different platforms at that time. This made Unix a standard in the newly created network. The resulting uniformity simplified the introduction of mandatory applications and protocols.


Unix is one of the first operating systems in computer history. Even today, the operating system and its further developments are still very popular, especially on internet servers. Read more about Unix and its history in our detailed article on Unix.

The benefits of Arpanet

Looking back, many see the main benefit of Arpanet as having paved the way for the internet. But Arpanet even brought enormous benefits to the associated universities in the first few decades after its development: it made it possible to run programs on remote computers. The corresponding service was, and is, known as 'Remote job entry' or NETRJS. In order to fully understand the significance of this, it is necessary to realize that the computing power of most computers at that time was far below what we are used to today. The fact that scientists were able to use the resources of connected computers made it possible to work much more efficiently.

Two applications that still characterize the global network were already introduced in the early days of Arpanet: FTP connections and e-mails. Both services were implemented in 1972. The file transfer protocol made it possible to exchange files between two hosts. E-mail, on the other hand, is something that every internet user is familiar with. At that time, the two programs READMAIL (read mail) and SNDMG (send message) were developed, which enabled Arpanet users to send and receive text messages electronically. Both were programmed by Ray Tomlinson, who worked for BBN Technologies at the time. We can also thank him for the @ sign, which is used to distinguish the name of the user from the name of the server.

Telnet is another service that is still part of the internet but has lost much of its importance in the meantime. The client-server protocol makes it possible to access another computer via a remote connection. With the input console, users can then execute commands on other computers to search databases or start programs, for example. Nowadays, however, this service is hardly used. Although Telnet offers a number of advantages (e.g. the protocol is cross-platform), it also has an obvious disadvantage: since the data exchange is completely unencrypted, the access points are entry points for cybercriminals. Instead of Telnet, encrypted SSH is used nowadays.


For more information about Telnet and how to use the service on your computer, read our article on Telnet - the system-wide remote protocol.

What does Arpanet mean for the internet?

Hardly anymore will deny that the internet as we know it today was decisively shaped by Arpanet. But what exactly does that mean? After all, Arpanet was not simply the internet with a different name. Some of the innovations that ARPA and BBN Technologies developed in the 1960s and 1970s are still used today – such as e-mails and the file transfer protocol. In principle, however, it was probably the concept of a decentralized, location-independent network that ultimately led to the internet.


The domain name system also originated in Arpanet but the computers in this network were still organized with numbers – by hand. There was a file (hosts.txt) for administration in which all network participants were entered. To be included in the list, you had to call the Network Information Center (NIC).

Other aspects of communication between computers have changed so much that the origins are difficult to recognize today. It is hard for many to imagine things that small routers are now capable of, were originally achieved by refrigerator-sized IMPs. Another decisive factor was the development of TCP/IP – a technology that was also inspired by the computer scientists at ARPA. Ethernet, a network technology, was also developed in the Arpanet environment and is still a standard when it comes to networking computers.

But what didn’t exist then – probably one of the most important differences between Arpanet and the internet – is the world wide web. The hypertext system was developed by Tim Berners-Lee in 1989, shortly before the Arpanet project was discontinued. Information was previously not accessible in the network of servers available at that time, and had to be requested individually from hosts – and even the first web browsers were still a long way off in 1969.

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