LearnViz CompSci
Home / Learn / Operating Systems / Shortest Job First

Beginner Topic 12 of 51 Operating Systems

Shortest Job First

Scheduling policy favoring the task with least remaining time.

How it works

Shortest job first picks the process with the smallest next CPU burst. It provably minimizes the average waiting time among non-preemptive schedules. The preemptive version, shortest remaining time first, switches when a shorter job arrives. Since burst lengths are unknown in advance, real systems estimate them with exponential averaging of previous bursts.

Step-by-step walkthrough

  1. Jobs arrive with known lengths.
  2. The shortest job runs first.
  3. The next shortest follows.
  4. The longest runs last.
  5. This minimizes average waiting time, but long jobs can starve.

Where it is used

Batch systems with known job lengths, database query schedulers and analysis in operating-systems courses use SJF. Its ideas appear in schedulers favoring short interactive tasks.

Common pitfall

Long jobs may starve if short ones keep arriving, so aging is needed. Burst predictions can be wrong. It is impractical when lengths cannot be known, and preemption adds context-switch costs. Do not confuse total job length with next CPU burst. Compare average waiting time with other algorithms using Gantt charts.

Where it fits in the course

Shortest Job First is topic 12 of 51 in Operating Systems, rated Beginner. It follows Round Robin Scheduling. The next topic is Priority Scheduling.

Practice and explore

How to study this topic

  1. Read the explanation above and restate the definition in your own words.
  2. Open the interactive lesson and answer its mini quiz.
  3. Read the common pitfall, then write a short example that avoids it.
  4. Check your understanding in the Operating Systems quiz, and revisit the topic if you miss a question.

Frequently asked questions

What is Shortest Job First?
Scheduling policy favoring the task with least remaining time. It belongs to Operating Systems and is a beginner-level topic.
Where do people use Shortest Job First?
Batch systems with known job lengths, database query schedulers and analysis in operating-systems courses use SJF.
What is the most common mistake with Shortest Job First?
Long jobs may starve if short ones keep arriving, so aging is needed.
What should I learn before this topic?
Start with Round Robin Scheduling, the topic just before it in Operating Systems.
How can I practice it?
Answer the mini quiz in the interactive lesson, then take the Operating Systems quiz.
Is Shortest Job First hard to learn?
It is a Beginner topic, so it works as an entry point. If the terms are new, read the explanation twice and try the visualizer before the quiz.
How long does it take to learn Shortest Job First?
Most learners can read the explanation and finish the interactive lesson in under an hour. Fluency comes from applying the idea, so plan a few short practice sessions with the quiz.
Which topics are related to Shortest Job First?
Round Robin Scheduling, Priority Scheduling, CPU Scheduling are closely connected. The full list is in the related topics section of this page.
What should I study after Shortest Job First?
Continue with Priority Scheduling, the next topic in Operating Systems.

Related topics