CPU Scheduling Algorithms: FCFS, SJF, and Round Robin |…

What Are CPU Scheduling Algorithms?

CPU scheduling is a fundamental aspect of operating system design, focusing on the allocation of processor time among processes. Each algorithm has its own set of rules and priorities for determining which process gets to run next.

The three main algorithms discussed here—First-Come-First-Served (FCFS), Shortest Job Next (SJF), and Round Robin—are essential in understanding how different strategies can impact system performance.

First-Come-First-Served (FCFS) Scheduling

In FCFS, processes are executed in the order they arrive at the ready queue. This is a simple and fair algorithm but can lead to inefficiencies if longer processes arrive after shorter ones.

The average waiting time for all processes under FCFS is generally higher compared to other algorithms like SJF or Round Robin.

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Shortest Job Next (SJF) Scheduling

SJF, also known as Shortest Remaining Time First (SRTF), prioritizes processes based on their estimated execution time. This can significantly reduce the average waiting and turnaround times.

However, SJF is prone to starvation if there are many short processes that keep preempting longer ones.

Round Robin Scheduling

In Round Robin scheduling, each process gets a fixed time slice (quantum) before being preempted and moved to the end of the queue. This ensures that no single process monopolizes the CPU for an extended period.

The choice of quantum size is critical; too large can lead to FCFS-like behavior, while too small can cause excessive context switching overhead.

Frequently asked questions

What is the main advantage of Round Robin scheduling?

Round Robin ensures that all processes get a fair share of CPU time and prevents any single process from monopolizing the CPU, which can happen with FCFS or SJF.

How does Shortest Job Next (SJF) reduce waiting times compared to FCFS?

By always running the shortest job next, SJF minimizes the total waiting time for all processes because shorter jobs are completed quickly and do not delay longer ones as much.

Why might Round Robin scheduling be inefficient with a very small quantum size?

A very small quantum can lead to frequent context switches, which increases overhead and reduces overall system efficiency. It essentially behaves like FCFS in such cases.

Can SJF cause starvation of long processes?

Yes, if there are many short jobs that keep preempting longer ones, the long processes may never get a chance to run, leading to starvation and poor system performance.

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Everything above runs in your browser — open CPU Scheduling — FCFS, SJF, Round Robin and change the parameters while it is running. Nothing is installed, nothing is uploaded, the whole model lives in one tab.

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