Day 01Part 12- Operating system for computer – Concept of Priority information in Operating system
Day 01Part 12- Operating system for computer – Concept of Priority information in Operating system
Contents [hide]
- 0.1 Concept of Priority in Operating Systems
- 0.2 What is Priority in an Operating System?
- 0.3 Types of Priority Scheduling
- 0.4 Static Priority Scheduling
- 0.5 Dynamic Priority Scheduling
- 0.6 Types of Priority Scheduling Algorithms
- 0.7 Example of Priority Scheduling
- 0.8 Advantages & Disadvantages of Priority Scheduling
- 0.9 Final Thoughts
- 0.10 Day 01Part 12- Operating system for computer – Concept of Priority information in Operating system
- 0.11 OPERATING SYSTEM Lecture Notes On
- 0.12 Operating System Concepts, 8th Edition
- 0.13 Operating System Concepts
- 1
Operating System – Concept of Priority (Day 01 – Part 12) - 2
Why Priority Is Used - 3
Types of Priority: - 4
How Priority Scheduling Works: - 5
Drawbacks of Priority Scheduling - 6
Summary Table
Concept of Priority in Operating Systems
In an Operating System (OS), priority plays a crucial role in process scheduling, ensuring that important tasks get CPU time before less critical ones. Priority scheduling is widely used in real-time systems, multitasking environments, and resource allocation.
What is Priority in an Operating System?
Priority refers to a numerical value assigned to a process that determines its importance in execution. A higher priority process gets executed before a lower priority process.
Types of Priority Scheduling
Static Priority Scheduling
Priority is assigned before execution and remains unchanged.
Example: Kernel processes, system tasks (always have high priority).
Used in real-time systems where priority is predefined.
Dynamic Priority Scheduling
Priority changes during execution based on factors like aging, CPU burst time, or I/O requirements.
Prevents starvation (low-priority processes getting delayed indefinitely).
Example: Aging Technique (low-priority processes gradually gain higher priority).
Types of Priority Scheduling Algorithms
| Algorithm | Description | Advantages | Disadvantages |
|---|---|---|---|
| Preemptive Priority Scheduling | Higher priority process preempts (interrupts) a lower one. | Ensures important tasks execute quickly. | Can cause starvation of low-priority processes. |
| Non-Preemptive Priority Scheduling | Higher priority process waits until the current process finishes. | Simple and avoids frequent context switching. | Long waiting times for lower-priority processes. |
Example of Priority Scheduling
Given processes and their priorities:
| Process | Priority | Burst Time (ms) |
|---|---|---|
| P1 | 3 | 10 |
| P2 | 1 | 5 |
| P3 | 4 | 2 |
| P4 | 2 | 8 |
Execution Order (Higher number = Higher priority):
P3 → P1 → P4 → P2 (Executed in descending order of priority).
Advantages & Disadvantages of Priority Scheduling
Efficient execution of critical tasks (useful in real-time systems).
Allows flexibility (different priority levels for different tasks).
Starvation problem (low-priority tasks may get delayed indefinitely).
Requires additional scheduling mechanisms like aging to prevent starvation.
Final Thoughts
Priority scheduling is widely used in real-time OS, process management, and multitasking systems. It ensures that high-priority tasks are executed efficiently, but proper techniques (like aging) must be used to prevent lower-priority processes from waiting indefinitely.
Would you like detailed examples, Gantt charts, or comparison with other scheduling algorithms?
Day 01Part 12- Operating system for computer – Concept of Priority information in Operating system
OPERATING SYSTEM Lecture Notes On
Operating System Concepts, 8th Edition
Operating System Concepts
Here’s a clear explanation of the Concept of Priority in Operating Systems, ideal for Day 01 – Part 12 of your study plan.
Operating System – Concept of Priority (Day 01 – Part 12)
What is Priority in Operating Systems?
In an Operating System (OS), priority is a value assigned to a process that helps the CPU decide which process to run first when multiple processes are ready to execute.
It is a fundamental concept in process scheduling to ensure that important or urgent tasks are given preferential access to CPU time.
Why Priority Is Used
- To manage multitasking
- To ensure faster response for critical processes (like system tasks or real-time apps)
- To prevent starvation or ensure fairness (when used with aging)
Types of Priority:
| Type | Description | Example |
|---|---|---|
| Static Priority | Fixed at the time of process creation | Real-time system may assign fixed priorities |
| Dynamic Priority | Can change during execution | Based on aging or process behavior |
How Priority Scheduling Works:
- The CPU scheduler selects the process with the highest priority.
- If two processes have the same priority, it may use FCFS (First Come First Serve).
- Can be preemptive or non-preemptive:
- Preemptive: A higher-priority process can interrupt a lower-priority one.
- Non-preemptive: The current process runs to completion even if a higher-priority one arrives.
Example:
Assume three processes with the following priorities (lower number = higher priority):
| Process | Burst Time | Priority |
|---|---|---|
| P1 | 5 ms | 2 |
| P2 | 3 ms | 1 |
| P3 | 4 ms | 3 |
CPU Order (Preemptive): P2 → P1 → P3
CPU Order (Non-Preemptive): Based on arrival time and priority
Drawbacks of Priority Scheduling
- Starvation: Low-priority processes may never get CPU time.
- Solution: Use Aging – gradually increase the priority of waiting processes.
Summary Table
| Term | Meaning |
|---|---|
| Priority | Rank of process importance |
| Preemptive | High-priority interrupts low-priority |
| Non-preemptive | Current process completes before switching |
| Starvation | Low-priority process gets ignored |
| Aging | Priority increases the longer a process waits |
Let me know if you’d like:
- Practice problems
- GATE-style MCQs
- Real-world OS examples (like Linux or Windows)
I’m happy to assist further!