It operated in two modes, one of which was full Instruction Set Simulator mode and provided Instruction step, conditional Program Breakpoint ("Pause") and storage alteration features for Assembler, COBOL and PL/1 programs. High level language (HLL) users were also able to see and modify variables directly at a breakpoint by their symbolic names and set conditional breakpoints by data content.
Many of the features were also available in "partial monitor mode" which relied on deliberately interrupting the program at pre-defined points or when a "program check" occurred.In this mode, processing was not significantly different from normal processing speed without monitoring.
It additionally provided features to prevent application program errors such as Program Check, "Wild branch" , and Program loop. It was possible to correct many errors and interactively alter the control flow of the executing application program. This permitted more errors to be detected for each compilation which, at the time, were often scheduled batch jobs with printed output, often requiring several hours "turnaround" before the next test run.