Messaging in the Early SDC Time-Sharing System

In the early 1960s, the time-sharing computer at the System Development Corporation had several messaging commands through which remotely logged in users communicated with one another and with the system operator. These commands were used for system operation and for sending information to remote users. They also permitted collaborative work such as joint debugging of multi-author programs, an activity now associated with the Internet. These capabilities appear to be the earliest documented implementation of text messaging and were in use before electronic mail was developed for time-sharing systems.