A Flexible and Inexpensive Method of Monitoring Program Execution in a Digital Computer

A method of monitoring the program execution in a digital computer on the basis of the flow diagram of the computing program has been devised. A comparatively low-cost equipment for monitoring a maximum of 64 boxes in a flow diagram has been constructed. The monitoring method is flexible and convenient in its application. It can be used in connection with relative or symbolic addresses, compilers, etc. The user must provide only a flow diagram drawn on translucent paper in a certain form and the information to correlate this diagram with the computing program. A subroutine modifies the computing program as needed for the monitoring purpose and restores it to its original form when the user so desires. The monitoring introduces only a very small increase in computing time, requiring for each call-up of a box in the flow diagram only a time amounting to that needed for two simple unconditional jumps. The monitor can be used to present during the computation a visual dynamic picture of the progress of the program and to register, on occurrence, the whereabouts of an interruption, thus facilitating the tracing of the error. The principle of the monitoring method and the subroutine program, and the essentials of the constructed monitor equipment, are described in detail.