TENEX and TOPS-20

In the late 1960s, a small group of developers at Bolt, Beranek, and Newman (BBN) in Cambridge, Massachusetts, began work on a new computer operating system, including a kernel, system call API, and user command interface (shell). While such an undertaking, particularly with a small group, became rare in subsequent decades, it was not uncommon in the 1960s. During development, this OS was given the name TENEX. A few years later, TENEX was adopted by Digital Equipment Corporation (DEC) for its new line of large machines to be known as the DECSYSTEM-20, and the operating system was renamed to TOPS-20. The author followed TENEX (or vice versa) on this journey, and these are some reflections and observations from that journey. He touches on some of the technical aspects that made TENEX notable in its day and an influence on operating systems that followed as well as on some of the people and other facets involved in the various steps along the way.