Os

1. NON PRE-EMPTIVE SCHEDULING
ALGORITHM
SUBJECT : OPERATING SYSTEM(SEMINAR) GROUP MEMBERS
CLASS : 4IT1 KETAN CHUNARA(53)
KEVAL PARMAR(54)
KHUSHAL PRAJAPATI(55)

2. OUTLINES
1. SCHEDULING
2. NON PRE EMPTIVE SCHEDULING
3. ADVANTAGES & DISADVANTAGES
4. FIRST COME FIRST SERVE
5. SHORTEST JOB FIRST
6. NON PRE EMPTIVE PRIORITY
7. PREEMPTIVE VS NON PREEMPTIVE
8. CONCLUSION

3. 3
SCHEDULING
 Scheduling is the process of selecting a process from a ready queue. And
allotting cpu to this process for execution.
 Scheduler is a part of operating system that allots computer resources to
the processes.
 Scheduler uses scheduling algorithms to decide which processes it must
allot to the cpu.

4. 4
CONT...
 Scheduling provides
1) better efficiency
2) reduce any kind of delay
3) even waiting time

5. 5
NON PRE EMPTIVE
SCHEDULING

6. 6
NON PRE-EMPTIVE SCHEDULING
 In non pre-emptive scheduling, once a process is selected, it runs to
completion until is blocked for an i/o devices or other events.
 This scheduling does not interrupt a process running CPU in the middle
of the execution.
 It wait till the process completes its CPU burst time, and it can allocate
the CPU to another process.

7. 7
ADVANTAGES OF NON PRE-EMPTIVE SCHEDULING
 It has a minimal scheduling burden.
 It is a very easy procedure.
 Less computational resources are used.
 It has a high throughput rate.
 It is a very simple method.

8. 8
DISADVANTAGES OF NON PRE-EMPTIVE SCHEDULING
 It has poor response time for process.
 A machine can freeze up due to bugs.
 Waiting time is high.

9. 9
TYPES OF NON PRE-
EMPTIVE SCHEDULING

10. 10
FIRST COME FIRST SERVE
1) selection area
 As the name suggests, the FCFS assign the CPU to the process that
arrive first in the ready queue.
 This means that the process that requests the CPU for its execution first
will get the CPU allocated first.
2) decision mode
 Once a process is selected, it run until either it is blocked for an io or
some event or it is terminated

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CONT...
3) implementation
 This method can be easily implemented by fifo.
 When CPU becomes free, a process from the first position in a queue is
selected to run.

12. 12
EXAMPLE OF FCFS

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CONT..
 Advantages of FCFS
1) it is a simplest form of scheduling algorithm.
2) its implementations is easy
 Disadvantages of FCFS
1) not efficient because average waiting time is high.

14. 14
SHORTEST JOB FIRST
1) selection area
• The process, that requires shortest time to complete execution, is
served first.
2) decision mode
• Once a process is selected, it run until either it is blocked for io
some other event or it is terminated.

15. 15
3) implementation
 This method can be easily implemented by FIFO.
 All processes in queue are sorted in ascending order based on their required
CPU bursts.
 When CPU becomes free, a process from the first position in a queue is
selected to run.
CONT...

16. 16
EXAMPLE OF SJF

17. 17
CONT..
 Advantages
1) less waiting time.
2) good response for short process.
 Disadvantages
1) it is difficult to estimate time required to complete execution.
2) starvation is possible for long process. Long process may wait forever.

18. 18
NON-PRE-EMPTIVE PRIORITY
1) selection area
 The process, that has highest priority is served first.
2) decision mode
 Once a process is selected, it runs until it blocks for an io or some event or it
terminates.

19. 19
CONT...
3) implementation
 This method can be implemented by using sorted fifo queue.
 All process in queue an sorted based on their priority with highest priority
process at front end.
 When cpu becomes free, a process from the first position in a queue is
selected to run.

20. 20
EXAMPLE OF NON PRE-EMPTIVE

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CONT...
 Advantages
1) priority is considered so critical process can get even better response time.
 Disadvantages
1) starvation is possible for low priority process. It can be overcome by using
technique called “aging”.
Aging : gradually increases the priority of process that wait in
the system for a long time.

22. 22
DIFFERENCE
PRE-EMPTIVE
 In this resources are allocated to a
process for a limited time.
 Process can be interrupted in
between.
NON-PRE-EMPTIVE
 Once resources are allocated to a
process the process holds it till it
completes its burst time or switches
to waiting state.
 Process can not be interrupted until
it terminates itself or its time is up.

23. 23
CONT...
 It has overheads of scheduling the
process.
 Flexible
 Cost associated
 Cpu utilization is high.
 Waiting time is less.
 Response time is less.
 It does not have overheads.
 Rigid
 No cost associated
 Cpu utilization is low.
 Waiting time is high.
 Response time is high.

24. 24
CONCLUSION
 Non-pre emptive scheduling algorithms offer efficiency, predictability,
fairness, lower overhead, and simplicity, making them suitable for various
computing environments, especially those with stringent timing
requirements or resource limitations.