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