Short Answer
Priority scheduling is a CPU scheduling algorithm in which each process is assigned a priority and the CPU is given to the process with the highest priority first. The priority can be based on system requirements, process importance, or user-defined values.
In this method, if a higher priority process arrives, it may preempt the current running process in preemptive scheduling. In non-preemptive scheduling, the running process continues until it finishes, and then the next priority process is selected.
Detailed Explanation:
Priority Scheduling Overview
Definition:
Priority scheduling is a CPU scheduling technique used by the operating system where each process is assigned a priority value. The CPU is allocated to the process with the highest priority first. If multiple processes have the same priority, they are scheduled based on arrival time.
Importance of Priority Scheduling:
This scheduling method is important because it ensures that important or critical tasks are completed first. It helps improve system efficiency in situations where some processes need faster execution than others, such as system tasks or real-time applications.
Working of Priority Scheduling
Priority Assignment
Meaning:
Each process is given a priority value when it enters the system.
Explanation:
The priority can be assigned based on different factors like process type, memory requirement, or user importance. A higher priority process is more important and gets CPU preference over lower priority processes.
Process Selection
Meaning:
The CPU selects the process with the highest priority from the ready queue.
Explanation:
All ready processes wait in a queue. The operating system checks their priority values and selects the one with the highest priority for execution first.
Execution of Process
Meaning:
The selected process is executed by the CPU.
Explanation:
Once a process is selected, the CPU starts executing it. In non-preemptive scheduling, the process runs until completion. In preemptive scheduling, it can be interrupted if a higher priority process arrives.
Types of Priority Scheduling
Preemptive Priority Scheduling
Meaning:
A running process can be stopped if a higher priority process arrives.
Explanation:
If a new process with higher priority enters the system, the CPU immediately switches to that process. This ensures that important tasks are handled quickly.
Non-Preemptive Priority Scheduling
Meaning:
Once a process starts execution, it cannot be interrupted.
Explanation:
The CPU completes the current process first, and only then selects the next highest priority process.
Features of Priority Scheduling
Priority-Based Execution
Explanation:
Processes are executed based on their importance rather than arrival time.
Flexible System
Explanation:
It allows different types of processes to be handled differently based on their priority level.
Support for Critical Tasks
Explanation:
Important system or real-time tasks are executed faster.
Advantages of Priority Scheduling
Fast Execution of Important Tasks
High priority processes are executed first, improving system responsiveness.
Flexible Control
System designers can assign priorities based on requirements.
Efficient for Real-Time Systems
It is useful in systems where urgent tasks must be completed quickly.
Disadvantages of Priority Scheduling
Starvation Problem
Low priority processes may never get CPU time if high priority processes keep arriving.
Complexity
Managing priorities and ensuring fairness increases system complexity.
Aging Required
Aging techniques are needed to increase priority of waiting processes to avoid starvation.
Example of Priority Scheduling
Suppose three processes P1, P2, and P3 have priorities 2, 1, and 3 respectively (1 is highest priority):
- P2 (priority 1) executes first
- P1 (priority 2) executes second
- P3 (priority 3) executes last
The CPU always selects the process with the highest priority first.
Importance in Operating System
Critical Task Handling:
It ensures important system tasks are executed first.
Better Resource Management:
CPU time is allocated based on process importance.
Used in Real Systems:
It is used in operating systems, embedded systems, and real-time applications.
Conclusion
Priority scheduling is an important CPU scheduling algorithm where processes are executed based on their priority levels. It ensures that important tasks are completed first and improves system efficiency. However, it may cause starvation for low priority processes if not managed properly.