DUCS (Display Unit Control System) was a teleprocessing monitor from CFS Inc. It was one of two early local teleprocessing packages for IBM's DOS/VSE environment. DUCS provided an interface and access method for programmers to 'talk' to monitors. Such access methods later became known as APIs. Initially written for the IBM 2260 running under DOS on IBM mainframes, the original product was free for IBM users. With the advent of DOS/VS and the IBM 3270 series terminals, the original author commercialized the product, circa 1970. The company added transparent remote access about 1972.