GPSS World



Computer simulation is a technique for predicting how a new, or altered, system will behave. It is more widely applicable than purely mathematical methods, and over the years it has saved its users millions of dollars. Most complex real world systems can be simulated. In fact, the list of applications of computer simulation would fill many pages, and is growing all the time.

Of the computer simulation languages developed to date, none has had more impact than GPSS, the General Purpose Simulation System. First developed by Geoffrey Gordon at IBM in the early 1960’s, GPSS is one of the world’s most popular simulation languages. Its award winning design has proven to be so robust that to this day it provides a rich basis for modern simulation environments. In addition, it has deeply influenced many other simulation languages that now rely on derivations of GPSS concepts.

Over recent years, the user interfaces presented by computer systems have evolved to benefit the human part of the system. Whereas at one time the computer was so expensive that considerable effort was justified in tending to its needs, now there is no excuse for any feature that needlessly detracts the user from his or her objectives.

GPSS World is primarily intended to be an extension of the user. It brings all the simulation primitives up to the user interface, and makes it easy to visualize and manipulate simulations. The result is that simulations can be developed, tested, and understood more quickly than ever before.

There is much more to GPSS World than just the GPSS language. Although your previous simulation experience is quite valuable, you should familiarize yourself with the new possibilities provided by the highly interactive GPSS World simulation environment.

About This Manual

This manual is divided into two major parts. Chapter 1 contains a tutorial on the use of GPSS World. The lessons in Chapter 1 lead you through most of the major features. All statements and windows are covered in detail in the GPSS World Reference Manual.

Chapter 2 contains a set of sample simulations based on a wide spectrum of applications. It contains examples from traffic control, inventory control, distribution, assembly, quality control, flexible manufacturing systems, PBX design, and many others. Sometimes, simulation techniques are best taught by example. For this reason, each example has been provided in machine readable form as part of the software package. This is discussed in Chapter 2 of the GPSS World Reference Manual.

We recommend that you study each example, then open the file in the GPSS World Model Window, and then follow the steps described in this manual. You can then interactively explore a wide variety of "What if?" scenarios. If you do not want to cover all the examples in Chapter 2, you should study the first 4 simulations before skipping to others.

The examples in Chapter 2 of this manual are intended to show a variety of techniques by which real world system behavior can be predicted using simulation techniques. The applications covered are only a tiny fraction of those amenable to simulation, but you may find some of the methods directly applicable to your own situation, even if the ultimate application is not identical to your own.

This tutorial manual is not complete with respect to the GPSS language. You will need to refer to the GPSS World Reference Manual for details on some of the GPSS statements used here.

How To Get Started

Before you start, you should have a Microsoft Windows compatible operating system installed on your computer and should have basic familiarity with that system. You should be familiar with Windows files and file specs, and the ways in which you can COPY, RENAME, and DELETE Windows files. There will be more discussion later on the differences between the command line, or file name copy and the icon copy of a file. Before beginning the tutorial, you should make sure that GPSS World is installed according to the directions in Chapter 2 of the GPSS World Reference Manual. Make sure that you have made a backup copy of the files in your GPSS World directory.

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