A Large-Scale, General-Purpose Electronic Digital Calculator: The SSEC

This paper, written and intended for publication in 1948, describes IBM's Selective Sequence Electronic Calculator (SSEC), which was placed in regular operation that year. The machine combined electronic computation with a memory system that included electronic, relay, and paper-tape sections. It executed programs stored exactly as data in any of the sections of memory, and could select, compute, or modify the program in a variety of ways. The speed and flexibility of the SSEC permitted it to solve many of the largest scientific problems of the day, including the generation of astronomical tables still used in space flight.