This document discusses priority scheduling in operating systems. Priority scheduling allocates CPU time to the ready process with the highest priority. It can be non-preemptive, where the running process continues until completion, or preemptive, where a higher priority ready process can preempt the running process. Priority scheduling aims to maximize CPU utilization and minimize wait time and response time, though it risks lower priority processes experiencing starvation if a high priority process monopolizes the CPU.

1. Priority Scheduling

2.  INDEX
Content Slide No.
1. Scheduling 3
2. Priority Scheduling 4
3. Non Pre-emptive Priority Scheduling 5
4. Pre-emptive Priority Scheduling 6
5. Advantages & Disadvantages 7
6. Bibliography 8

3. Scheduling
 Scheduling is the activity of picking a process from ready
state and allocating it to CPU.
 The short term schedular is responsible for this process.
 CPU utilization should be high
 Turnaround time should be low
 Response time should be low
 Waiting time should be low
 Throughput should be maximun
 Performance Criteria for Scheduling
Algorithm

4. Priority Scheduling
 This algorithm schedule a process based on the priority.
 Out all of the available processes highest priority process gets the CPU.
 If a tie occur then it follows FCFS, if again a tie occur then lowest id
process is selected.
 Generally the lower the priority number, the higher is the priority of the
process.

5.  Non Pre-emptive Priority Scheduling
 In the non pre-emptive version of priority scheduling once a process gets the
CUP it will execute until its completion.
 Example:
Process Priori
ty
AT BT CT TAT WT RT
P1 2 0 11 11 11 0 0
P2 0 5 28 39 34 6 6
P3 3 12 2 60 48 46 46
P4 1 2 10 49 47 37 37
P5 3 9 9 58 49 40 40
Total 217 189 129 129
Average 43.4 37.8 25.8 25.8
P1 P2 P4 P5 P3
0 11 39 49 58 60

6.  Pre-emptive Priority Scheduling
 In the pre-emptive version when a process arrive the ready state, then it is compared
with the other processes and with the process currently executing. Then the process
with highest priority is allocated the CPU.
 Example:
Process Priori
ty
AT BT CT TAT WT RT
P1 2 0 11 49 49 38 0
P2 0 5 28 33 28 0 0
P3 3 12 2 60 48 46 46
P4 1 2 10 40 38 28 0
P5 3 9 9 58 49 40 40
Total 240 212 152 86
Average 48 42.4 30.4 17.2
P1 P4 P2 P4 P1 P5 P3
0 2 5 33 40 49 58 60

7. Advantages
 Processes are executed based their priorities.
 Provides a good mechanism where relative importance of each
process may be precisely defined
 Disadvantages
 If high priority process takes a lot of time, lower priority process may
starve and be postponed indefinitely. This situation is called
starvation.
 Deciding which process will get which priority level.

8. Bibliography
 https://static.javatpoint.com/operating-system/images/os-priority-
scheduling.png
 https://www.geeksforgeeks.org/priority-cpu-scheduling-with-different-
arrival-time-set-2/
 https://media.geeksforgeeks.org/wp-content/cdn-
uploads/20220727105424/Screenshot-77.png