Question

9. SJN Gantt Chart with Completion Times

Answer 1

To create a Gantt chart for the Shortest Job Next (SJN) scheduling algorithm, we first need a set of processes along with their burst times (execution times). After determining the order in which the jobs will be executed according to SJN, we can compute the completion times and visualize the Gantt chart.

### Example Process Information

Let's assume we have the following processes:

| Process | Burst Time |
|---------|------------|
| P1 | 4 |
| P2 | 2 |
| P3 | 1 |
| P4 | 3 |

### Step 1: Order the Processes

In the SJN scheduling algorithm, processes are executed in the order of their burst time, from shortest to longest. For our example:

1. P3 (1)
2. P2 (2)
3. P4 (3)
4. P1 (4)

### Step 2: Calculate Completion Times

Now, let's calculate the completion times for each process:

- **P3**: Starts at time 0, completes at time 1 (0 + 1)
- **P2**: Starts at time 1, completes at time 3 (1 + 2)
- **P4**: Starts at time 3, completes at time 6 (3 + 3)
- **P1**: Starts at time 6, completes at time 10 (6 + 4)

### Completion Times Table

| Process | Burst Time | Completion Time |
|---------|------------|------------------|
| P3 | 1 | 1 |
| P2 | 2 | 3 |
| P4 | 3 | 6 |
| P1 | 4 | 10 |

### Step 3: Create the Gantt Chart

The Gantt chart represents the execution timeline of the processes. Based on our calculation, it would look like this:

```
| P3 | P2 | P4 | P1 |
0 1 3 6 10
```

### Summary

In this case, the final Gantt chart representation shows the sequence of processes as executed by SJN, along with their respective completion times. The completion times provide a quick reference for understanding when each process finishes its execution.