Tutorial 2 : Practising with Scheduling Algorithm

In this tutorial, we will look into using ALExSIM-USAS to help one practising with scheduling algorithm.

Let say you are a student in the Operating System course, and is given an exercise on scheduling algorithm which comprises a list of process details as follow: 

You are asked to manually calculate and perform First-Come-First-Serve scheduling algorithm for the process details above, and determine the following:

• the completion time
• the turnaround time, and
• the average waiting time.

Lets assume that you manage to produce some calculated information as your answer.

But how to verify the answer (other than waiting for the answer scheme from the instructor or just relying on luck)? In this situation, USAS can help to prepare the expected answer or the answer scheme.

Using ALExSIM-USAS to prepare the result

First what you need to do is to prepare the 'empty' process details table. Click the Manual Data Settings tab. The given exercise data contain 5 processes, so enter value 5 for the ‘number of process(es)' and click the Generate empty fields button.

Manual Data Settings section

Once the empty table is generated in Customize Process Details section, enter the data from the exercise in the generated table. (You may use the same priority number for all processes if the data are not available from the exercise)

After manually editing the process details according to the exercise

Then select the scheduling algorithm required for the exercise, which is the First-Come-First-Serve (FCFS). (By default, this algorithm is already selected by USAS).

Click the Run Simulation button to produce the expected result.

By default, in the result section will display the Summary tab which shows the Average Waiting Time and the Gantt charts (character-based or graphical-based), as follows:

The generated result shown in the bottom section (Summary tab).

This may not be enough. To view more details, click the Details tab, which displays the other required details such as the completion time, waiting time, turnaround time and others.

The generated result displayed in Details tab

Advantage in using ALExSIM-USAS for self-practising

USAS provides more advantages in helping student to do self-exercise. You may create a lot of different settings for the process details as your own 'question' for self-exercise and practice, calculate the answer manually and then easily verify your answer. Produce your own answer first and then verify.

An instructor for Operating System course/subject also can get benefits from using USAS. Since USAS can automate the calculation for the average waiting time, etc., this will help the instructor to produce answer scheme for student's exercise or for examination, faster and much easier (especially for the preemptive algorithm such as SJF preemptive and Round-Robin).