On-line Process Synthesizer version 4 

Modification by Malcom Jones of OPS-3 to ensure greater functionality: running under MULTICS on GE 645, implemented in PL/I and featuring data types - sets, queues tables.

Conceptual switch from Events (SIMSCRIPT) to Activity (SOL and SIMULA)

Related languages
OPS-3 => OPS-4   Evolution of
OPS-4 => SIMPL   Evolution of

  • Jones, Malcolm M. "On—line simulation" view details
          in Proceedings of the 22nd national ACM conference 1967, Washington, D.C. view details
  • Jones, M.M. "Incremental Simulation On A Time-Shared Computer" Massachusetts Institute of Technology, Project MAC report no. MAC-TR-48 January 1968 view details Abstract: This thesis describes a (proposed) system that will allow simulation models to be built and tested incrementally. Called OPS-4, the system is designed to operate under Multics. It represents a major expansion and improvement of the OPS-3 system in CTSS and also includes many features adapted from other simulation languages. The PL/I language, augmented by additional statements and new data objects, provides the basis for designing models in OPS-4. Desirable features for an incremental simulation system are listed and it is shown how OPS-4 incorporates these features, whereas other current simulation systems satisfy only some of them and are not suitable for use in a time-shared environment.

    Some of the particular problems solved by OPS-4 are the implementation and identification of many data bases associated with one procedure, the achievement of apparent simultaneity of execution of many procedures, the use of multiple processes for achieving asynchronous operation of the simulation system, and a combination interpreter and incremental compiler that allows both the data base and the model structure to be changed and the model immediately executed without the need for complete recompilation.

    OPS-4 includes extensive debugging and tracing features that are prticularly adapted to the on-line, interactive environment provided by Multics. OPS-4 also makes extensive use of list structures, so the techniques of memory compacting to reduce unnecessary paging activity are described. Numerous methods for obtaining statistical measures of a model's performance and plotting its dynamic behavior are provided in OPS-4. The use of graphical displays for debugging and dynamically monitoring a model's performance are discussed. A simplified model of page and segment fault handling in Multics illustrates some of the features OPS-4 provides to allow the user to continuously interact with a model during its construction, testing, and running phases. It also illustrates how the user himself may portray portions of a model that are not yet defined.
          in Proceedings of the 22nd national ACM conference 1967, Washington, D.C. view details