The ARPANET/TENEX Primer and the MSG Message Handling Program
This is a 1977 technical primer from the Defense Technical Information Center on the ARPANET and TENEX computer systems and the MSG message handling program, written for computer users and programmers. The one picture is a line map of the United States showing ARPANET host sites linked by lines, with a dotted binding edge on the left, and a designer might take its schematic network-diagram look, with labelled nodes joined by thin straight and angled connectors, as a model for a clean technical diagram.
