Focal Notes and Background

This document provides a firsthand account of the origins, development, and historical significance of FOCAL (Formula Calculator), an early interactive, interrupt-driven programming language created by Richard M. Merrill for Digital Equipment Corporation (DEC) minicomputers. The text covers the development process, technical innovations like re-entrant code and interactive multi-user support, anecdotes about field use and debugging, and a catalog of original artifacts donated to the Computer History Museum.