The Queuiac: An Electromechanical Analog for the Simulation of Waiting-Line Problems

Of interest to the Operations Research Office for several years has been the problem of improving the efficiency of Army communications systems. Involved in these studies, besides obvious problems of communications equipments, are problems of organization and human handling operations. To understand and offer solutions to these latter problems, electromechanical simulation equipment has been developed that displays the network of handling operations and provides estimates of congestion at any or all points in the system. In the analog each node consists of a display and register unit upon which columns of lights represent items in a waiting line. Distributions of arrival times of input items and servicing times are programmed on standard teletype tape fed to the analog by teletype transmitters. The register unit at each point of the network displays the queue, computes state occupancy times, and provides estimates of state probabilities. Continuous records of the system states are maintained by pen recorders so that individual delay times and empirical estimates of their distributions may be obtained. The register units may be connected in parallel or tandem, representing various sequential or parallel operations. Available as important queue disciplines are the handling of multiple inputs on a priority basis and the automatic adjustment of servicing rates according to transient loads.