SIMSCRIPT: A Pioneering Simulation Language from the RAND Corporation
In the early 1960s, the field of computer simulation was in its infancy, and the need for specialized languages to facilitate the creation of large-scale discrete event simulations was becoming increasingly apparent. One of the earliest and most influential simulation languages to emerge from this period was SIMSCRIPT, a language developed by Harry Markowitz and Bernard Hausner at the RAND Corporation in 1963. SIMSCRIPT played a pivotal role in shaping the development of simulation software, and its legacy continues to influence modern simulation tools. This article explores the origins, development, features, and impact of SIMSCRIPT on the world of computer simulation.
Origins and Development
SIMSCRIPT was conceived by Harry Markowitz, a renowned economist and Nobel laureate, and Bernard Hausner, an engineer at the RAND Corporation. The language was created to meet the needs of large, complex simulations that could model real-world systems in industries such as defense, logistics, and manufacturing. At the time, simulation was a labor-intensive process that often involved writing custom code in low-level programming languages such as Fortran. Markowitz and Hausner sought to simplify the process by creating a high-level, English-like simulation language that could be more easily understood and used by non-programmers, particularly those involved in fields like operations research and management science.
The language was implemented as a Fortran preprocessor on the IBM 7090, one of the most powerful computers of the era. As a preprocessor, SIMSCRIPT was designed to generate efficient Fortran code that could be executed on the IBM 7090, making it possible to run large-scale simulations on the hardware available at the time. The early versions of SIMSCRIPT were highly specialized, focusing on discrete event simulation, which models the operation of systems in which events occur at discrete points in time.
The success of SIMSCRIPT at RAND Corporation led to its commercialization by Markowitz’s company, California Analysis Center, Inc. (CAC). In the years that followed, the company released several proprietary versions of SIMSCRIPT, including SIMSCRIPT I.5 and SIMSCRIPT II.5. These versions of the language were designed to address the evolving needs of the simulation community, offering more powerful features and improved performance.
Features and Capabilities
SIMSCRIPT was designed to be a flexible and powerful simulation language, with a focus on ease of use and accessibility. The language adopted a free-form, English-like syntax that allowed users to describe simulation models in a way that was more intuitive than the rigid, structured syntax of traditional programming languages. This made SIMSCRIPT particularly appealing to users with limited programming experience who needed to develop complex simulations quickly and efficiently.
One of the key features of SIMSCRIPT was its ability to model discrete event systems. In a discrete event simulation, the state of the system changes only at specific points in time, which are triggered by events. For example, in a simulation of a manufacturing process, an event might represent the arrival of a new part, the completion of a task, or the failure of a machine. SIMSCRIPT provided the tools to define these events and their interactions, allowing users to model a wide range of systems in fields such as transportation, telecommunications, and healthcare.
SIMSCRIPT also supported hierarchical modeling, which allowed users to define complex systems in terms of simpler subsystems. This made it easier to manage large models by breaking them down into smaller, more manageable components. The language provided a rich set of data structures, including arrays, lists, and queues, which enabled users to represent complex relationships between entities in the system.
Another notable feature of SIMSCRIPT was its support for time-based simulation. The language allowed users to define the timing of events and the progression of time within the simulation. This was particularly important for modeling systems that depended on the timing of events, such as queuing systems or production lines.
Despite its power and flexibility, SIMSCRIPT was not without its limitations. One of the challenges of using SIMSCRIPT was its steep learning curve, particularly for users who were not familiar with simulation concepts or programming in general. Additionally, the early versions of the language were closely tied to specific hardware platforms, such as the IBM 7090, which limited its portability to other systems. Over time, however, the language was adapted to work on a wider range of platforms, and commercial versions of SIMSCRIPT offered improved usability and performance.
SIMSCRIPT’s Influence on Modern Simulation Languages
SIMSCRIPT was one of the earliest examples of a specialized simulation language, and its development had a lasting impact on the field of computer simulation. One of the most significant ways in which SIMSCRIPT influenced modern simulation languages was through its role in the development of Simula, the first object-oriented programming language. Simula, which was developed by Ole-Johan Dahl and Kristen Nygaard at the Norwegian Computing Center (Norsk Regnesentral) in the mid-1960s, drew heavily on ideas from SIMSCRIPT, particularly in its approach to modeling systems as discrete events.
Simula’s introduction of object-oriented programming concepts, such as classes and objects, was a direct result of the experiences gained from working with SIMSCRIPT. While SIMSCRIPT itself did not incorporate object-oriented programming, the language’s emphasis on modularity and hierarchical modeling laid the groundwork for the object-oriented approach that would become a dominant paradigm in software development.
In addition to influencing the development of Simula, SIMSCRIPT also paved the way for other simulation languages and tools. Languages such as GPSS (General Purpose Simulation System) and Arena, as well as modern simulation software like AnyLogic and Simul8, owe much of their design to the concepts introduced by SIMSCRIPT. These tools built on SIMSCRIPT’s approach to discrete event simulation, offering more powerful features and greater ease of use.
Commercialization and Legacy
The commercialization of SIMSCRIPT by California Analysis Center, Inc. (CAC) marked the beginning of the language’s widespread use in industry and academia. Over the years, the company released several versions of the language, including SIMSCRIPT I.5 and SIMSCRIPT II.5. These commercial versions introduced new features, improved performance, and enhanced user interfaces, making it easier for users to create and run large-scale simulations.
Despite the success of the commercial versions, the rise of alternative simulation tools and the increasing power of general-purpose programming languages such as C and Fortran led to a decline in the popularity of SIMSCRIPT. By the late 1980s, other simulation languages and software packages had become more widely adopted, and SIMSCRIPT was largely supplanted by newer technologies.
Nevertheless, the legacy of SIMSCRIPT lives on in the simulation community. The language’s emphasis on modeling discrete event systems, its free-form syntax, and its hierarchical approach to system design continue to influence modern simulation tools. Moreover, SIMSCRIPT’s role in the development of object-oriented programming concepts through its influence on Simula remains one of its most enduring contributions to the field of computer science.
Conclusion
SIMSCRIPT was a groundbreaking language that played a pivotal role in the early development of simulation software. Conceived at the RAND Corporation in the early 1960s, the language addressed the growing need for specialized tools to model complex, real-world systems. Its English-like syntax, support for discrete event simulation, and hierarchical modeling capabilities made it a powerful tool for researchers and engineers in a variety of fields. Although it was eventually commercialized and largely supplanted by newer technologies, SIMSCRIPT’s influence on the development of simulation languages and its role in the evolution of object-oriented programming cannot be overstated. Today, SIMSCRIPT is remembered as one of the foundational languages in the history of computer simulation, and its legacy continues to shape the field.