What was ARPANET?

In Summary:

ARPANET was an experimental network, set up in 1969 by the Department of Defense Advanced Research Projects Agency (ARPA). ARPANET enabled its users to share information and resources, and served as a test-bed for networking technologies.

One result of the research done on ARPANET was the development of the TCP/IP protocols, which govern the way data is transmitted and shared across networks. The widespread use of TCP/IP helped create the Internet as we know it today.

ARPANET continued to expand, and in 1983 split into two networks - ARPANET and MILNET. Finally, in 1990, ARPANET was dissolved, with most of the sites that had been on ARPANET connecting to the faster NSFNET.