By the 1950s, computers were an established part of business. Personal computers were still a few decades away, but the government, universities, and many large industries were using them. However, computers could not yet easily communicate directly with each other.

A few early computer systems included multiple computers that were designed to work with each other to share data and perform calculations more quickly than a single computer could. For example, the U.S. Department of Defense’s Semi-Automatic Ground Environment (SAGE) system used existing telephone lines to carry data from multiple radar receivers to central computer systems that could analyze the data and determine how to react in the event of a hostile action. The computer systems would then send the response to military bases over the same telephone network (Lincoln Laboratory, 2014).

In 1964, Dartmouth College set up the first time-sharing network that allowed multiple users to access a single computer at the same time. The network eventually incorporated users from other universities into the network (Dartmouth Time-Sharing System, n.d.).