<SImulation> (OPS) A system for discrete SImulation under CTSS developed by M. Greenberger at MIT ca. 1964. [Sammet 1969, p.660. VerSIons: OPS-3, OPS-4. "On- line Computation and SImulation: The OPS-3 System", M. Greenberger et al, MIT Press 1965]. (2003-04-05)