CPU Scheduling Algorithm SJF: A Comprehensive Guide

 The Shortest Job First (SJF) CPU Scheduling algorithm is one of the most commonly used scheduling algorithms in computer operating systems. In this algorithm, the CPU selects the process with the shortest expected execution time to execute first. In this article, we will provide a detailed overview of the SJF algorithm, its advantages and disadvantages, and its use in modern computing.

CPU Scheduling Algorithm SJF

How Does SJF Algorithm Work?

The SJF algorithm works by choosing the process with the shortest expected execution time from the ready queue. When a process arrives in the system, the CPU compares the execution time of the process to the execution time of the current running process. If the newly arrived process has a shorter expected execution time, the CPU suspends the current process and starts executing the new process. If two processes have the same expected execution time, the CPU can use other criteria to break the tie.

Types:

SJF algorithm is classified into two types,

1.Pre-emptive 

In preemptive SJF algorithm, the CPU can interrupt the currently executing process if a shorter process arrives, and the new process is executed immediately. 

2.Non-pre-emptive

 In non-preemptive SJF algorithm, the CPU waits until the current process finishes its execution before starting the new process.

Types of CPU Scheduling Algorithm SJF

Advantages of SJF Algorithm

⦁ Shorter Waiting Time: The SJF algorithm reduces the waiting time of short processes, as the CPU executes the shortest process first.

⦁ Higher Throughput: The SJF algorithm increases the overall throughput of the system by executing more processes per unit of time.

⦁ Optimal: The SJF algorithm is optimal in terms of minimizing the average waiting time and turnaround time when all the process execution times are known.

⦁ Fairness: The SJF algorithm is fair in terms of CPU utilization. It ensures that every process gets an equal opportunity to run on the CPU.

Disadvantages of SJF Algorithm

⦁ Impractical for Unknown Execution Times: The SJF algorithm requires knowledge of the execution time of each process beforehand. In real-world situations, it is challenging to determine the exact execution time of a process.

⦁ Starvation: The SJF algorithm can lead to starvation of long processes if many short processes are in the ready queue.

⦁ Complexity: Implementing the SJF algorithm can be complex and requires sophisticated algorithms to estimate the execution time of each process.

⦁ Unfairness: In non-preemptive SJF algorithm, long processes might have to wait for an extended period, leading to unfairness.

Conclusion:

In conclusion, the SJF algorithm is a widely used CPU scheduling algorithm that prioritizes processes with the shortest expected execution time. It is an effective algorithm for reducing waiting times and increasing the throughput of the system. The SJF algorithm has its strengths, such as higher CPU utilization, fairness, and optimal performance, but it also has its weaknesses, such as complexity, impracticality for unknown execution times, and the risk of starvation. It is essential to consider these advantages and disadvantages carefully when choosing the SJF algorithm for a particular application.