Shortest Job First (SJF) CPU Scheduling Algorithm: Minimizing Average Waiting Time

Learn about the Shortest Job First (SJF) CPU scheduling algorithm, which prioritizes processes with shorter burst times to minimize average waiting time. This guide explains SJF's operation, its advantages, and the challenges of accurately predicting burst times.

Shortest Job First (SJF) CPU Scheduling Algorithm

Understanding SJF Scheduling

The Shortest Job First (SJF) scheduling algorithm prioritizes processes with shorter burst times (the time a process needs the CPU). The OS selects the process with the shortest burst time from the ready queue to run next. This approach aims to minimize the average waiting time for all processes and increase overall system throughput. However, accurately predicting a process's burst time in advance is challenging, making precise implementation difficult.

Advantages of SJF

• High Throughput: Completes many jobs quickly.
• Low Average Waiting Time: Processes wait less, on average.
• Low Average Turnaround Time: Jobs complete faster, on average.

Disadvantages of SJF

• Starvation: Long jobs might never get scheduled if shorter jobs keep arriving.
• Difficult Implementation: Predicting burst times accurately is nearly impossible.

SJF Example

Let's consider five processes (P1-P5) with their arrival and burst times:

The scheduler selects the process with the shortest burst time from the ready queue. The Gantt chart would show that the processes are scheduled according to this.

Average Waiting Time: (0 + 7 + 2 + 7 + 14) / 5 = 6