Priority Scheduling Algorithm

What is Priority Scheduling?

Priority Scheduling is a scheduling algorithm that assigns a priority to each process and executes the process with the highest priority first.

Types of Priority Scheduling

• Preemptive Priority Scheduling: The operating system can preempt the currently running process if a higher-priority process arrives.
• Non-Preemptive Priority Scheduling: The operating system does not preempt the currently running process, even if a higher-priority process arrives.

How Priority Scheduling Works

• Assign a priority to each process.
• Sort the processes in descending order of their priorities.
• Execute the process with the highest priority first.

Example Calculation

Process	Arrival Time	Burst Time	Priority
P1	0	5	2
P2	0	3	1
P3	0	1	3
P4	0	2	4

Gantt Chart (Non-Preemptive)

Time	Process
0-2	P4
2-3	P3
3-6	P1
6-9	P2

Calculation of Waiting Time and Turnaround Time

Process	Arrival Time	Burst Time	Completion Time	Turnaround Time	Waiting Time
P4	0	2	2	2	0
P3	0	1	3	3	2
P1/td>	0	5	6	6	1
P2	0	3	9	9	6

Average Waiting Time and Turnaround Time

Average Waiting Time = (0 + 2 + 1 + 6) / 4 = 9 / 4 = 2.25

Average Turnaround Time = (2 + 3 + 6 + 9) / 4 = 20 / 4 = 5