2025 ASEE Annual Conference & Exposition

Traditional courses in Operating Systems cover many topics that are difficult to understand, including CPU scheduling algorithms. One approach to helping students test their understanding is using a paper-based worksheet that allows them to record which process runs at each point in time. Another approach, which has been used in the past with apparent success, is the use of simulations. However, many of these simulations have been lost to the ravages of time and are not readily accessible today. Others are designed to show students the solutions, but do not help them assess their own understanding. None of the papers we found that describe these simulations performed a rigorous study on the learning outcomes of students using the tools.

This paper describes a simulation, called GraySim, that allows students to practice and receive dynamic feedback on their understanding of five common scheduling policies. GraySim allows students to specify the policy they wish to practice. Students then input their answer for the policy, indicating which process is running at each point in time, and can then view feedback on their solution. If their solution is correct, the simulator tells them so; otherwise, the feedback identifies the types of errors that the student has made, such as scheduling a process for too little or too much time, scheduling the process before its arrival time, or scheduling it at the same time as another process. The feedback also offers policy-specific feedback, such as that the student has preempted a process when using a non-preemptive policy or that they appear to have used the incorrect policy.

We deployed this simulation to approximately 50 undergraduate students enrolled in our current offering of Operating Systems. We asked students to fill out a survey about their experience with GraySim. The paper also compares their success on a scheduling question from a mid-term exam to that of the previous year’s students who did not have access to GraySim. In the paper, we discuss the results of both the qualitative survey and the quantitative learning outcomes. We close the paper with a discussion of the limitations of the study and threats to its validity as well as a discussion of future research.