Day 01Part 01- Operating System for gate Computer Science โ Introduction to scheduling algorithm.
Day 01Part 01- Operating System for gate Computer Science โ Introduction to scheduling algorithm.
Hereโs a clear and structured explanation for:
Contents [hide]
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Day 01 โ Part 01: Operating System for GATE CSE- 1.1
Topic: Introduction to Scheduling Algorithms - 1.2
1. What is CPU Scheduling? - 1.3 Why Scheduling is Important in OS (GATE Point of View):
- 1.4
2. Types of Schedulers in OS: - 1.5
3. Scheduling Criteria (Very Important for GATE MCQs) - 1.6
4. Classification of Scheduling Algorithms - 1.7
5. Brief Intro to Common Scheduling Algorithms - 1.8
GATE Question Examples - 1.9
Formula Quick Recap - 1.10
Recommended for GATE CSE Preparation - 1.11 Day 01Part 01- Operating System for gate Computer Science โ Introduction to scheduling algorithm.
- 1.12 OPERATING SYSTEMS Unit โ I 1.1 Introduction
- 1.1
Day 01 โ Part 01: Operating System for GATE CSE
Topic: Introduction to Scheduling Algorithms
1. What is CPU Scheduling?
CPU Scheduling is the process of selecting one process from the ready queue to execute next on the CPU.
In a multiprogramming system, multiple processes are in memory, and the CPU scheduler picks one of the processes to run.
Why Scheduling is Important in OS (GATE Point of View):
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Improves CPU utilization
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Minimizes waiting time, turnaround time
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Maximizes throughput and responsiveness
2. Types of Schedulers in OS:
| Scheduler Type | Role |
|---|---|
| Long-Term | Decides which jobs are admitted to the system |
| Short-Term | Picks from ready queue โ allocated to CPU (CPU Scheduling) |
| Medium-Term | Suspends/resumes processes (used for swapping) |
3. Scheduling Criteria (Very Important for GATE MCQs)
| Criterion | Description |
|---|---|
| CPU Utilization | Keep CPU as busy as possible (ideal: 100%) |
| Throughput | No. of processes completed per unit time |
| Turnaround Time | Completion time โ Arrival time |
| Waiting Time | Turnaround Time โ Burst Time |
| Response Time | First response โ Arrival time |
| Fairness | No starvation, all processes get chance |
4. Classification of Scheduling Algorithms
| Type | Examples |
|---|---|
| Non-Preemptive | FCFS, SJF (non-preemptive), Priority (non-preemptive) |
| Preemptive | SRTF, Round Robin, Priority (preemptive), Multilevel Queue |
5. Brief Intro to Common Scheduling Algorithms
| Algorithm | Key Idea |
|---|---|
| FCFS | First Come First Serve โ easy but can cause convoy effect |
| SJF | Shortest Job First โ optimal avg. waiting time, may cause starvation |
| SRTF | Preemptive version of SJF |
| Priority | Processes scheduled based on priority |
| Round Robin | Each process gets a time quantum โ good for time-sharing systems |
GATE Question Examples
Q (GATE 2017):
Which of the following scheduling algorithms could result in starvation?
Answer: SJF (non-preemptive) and Priority (if lower priority never gets CPU)
Formula Quick Recap
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Turnaround Time (TAT) = Completion Time โ Arrival Time
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Waiting Time = TAT โ Burst Time
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Response Time = First Response โ Arrival Time
Recommended for GATE CSE Preparation
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Practice 10โ15 scheduling problems with Gantt charts
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Focus on edge cases (e.g., same arrival time, preemption mid-process)
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Learn to compute average waiting and turnaround time
Would you like:
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Gantt Chart problems with solutions? -
Video script/slide for this lesson? -
Quiz on these concepts?
Let me know and Iโll prepare it!