This document discusses various CPU scheduling algorithms. It describes non-preemptive and preemptive scheduling and covers scheduling algorithms like first-come first-served (FCFS), shortest job first (SJF), priority scheduling, round robin, multi-level queue scheduling, and multi-processor scheduling. It provides details on how each algorithm works and its advantages and disadvantages.

1. Video Lecture and E-Content Created by
R.D.SIVAKUMAR,M.Sc.,M.Phil.,M.Tech.,
Assistant Professor of Computer Science &
Assistant Professor and Head, Department of M.Com.(CA),
Ayya Nadar Janaki Ammal College,
Sivakasi – 626 124.
Mobile: 099440-42243
e-mail : sivamsccsit@gmail.com website: www.rdsivakumar.blogspot.in
SCHEDULING ALGORITHMS

2. CPU Scheduling algorithms decide which of the processes in the
ready queue is to be allocated to the CPU.
CPU SCHEDULING ALGORITHMS

3. Non Pre-emptive scheduling
Pre-emptive scheduling.
CPU SCHEDULING TYPES

4. Once the CPU has been allocated . In non-preemptive scheduling the
process keeps the CPU until it releases the CPU either by terminating or
by switching to the waiting state.
NON-PRE-EMPTIVE SCHEDULING

5. In pre-emptive scheduling, the process keeps the CPU until interrupt
occurs.
PRE-EMPTIVE SCHEDULING

6. It is Simplest CPU scheduling algorithm
It is non-preemptive scheduling algorithm
In this scheme, the process that requests the CPU first is allocated the CPU first
(or) the process enter the ready queue first is served first.
FIRST-COME, FIRST SERVED SCHEDULING

7. Waiting time
Waiting time = starting time – arrival time
Turn around time
Turn around time= finished time – arrival
time (Burst time + waiting time).
Response time
In non preemptive scheduling algorithm, the
average waiting time is equal to the average response time.
FCFS

8. In this scheme, the CPU is assigned to the process that has the
smallest next CPU burst.
It may be either preemptive (or) non preemptive.
SHORTEST JOB FIRST SCHEDULING

9. In preemptive shortest job first, the new process may have a
shorter next CPU burst than the currently executing process, it
will preempt the currently executing process.
Preemptive SJF scheduling is some times called “Shortest-
remaining-time-first Scheduling”.
PREEMPTIVE SJF SCHEDULING ALGORITHM

10. Comparing to FCFS algorithm, almost 50% waiting time saved in SJF.
ADVANTAGES

11. Big jobs are waiting so much time for CPU.
DISADVANTAGES

12. In this scheme, a priority is associated with each process and
the CPU is allocated to the process with the highest priority.
Equal priority processes are scheduled in FCFS order.
Priorities are indicated by range of numbers.
Low numbers represent the high priority
It may be either preemptive or non preemptive
PRIORITY SCHEDULING ALGORITHM

13. In preemptive priority scheduling algorithm, the new process may have
higher priority than the currently executing process, it will preempt the
currently executing process.
PREEMPTIVE
PRIORITY SCHEDULING ALGORITHM

14. It is a preemptive scheduling algorithm.
It is designed for time sharing systems.
In round robin scheduling, the ready queue is treated as a
circular queue.
In this scheduling, the CPU switches between the processes
when the time quantum expires.
ROUND ROBIN SCHEDULING

15. In this algorithm, the ready queue is partitioned with number of
ready queue.
Each ready queue has its own scheduling algorithm.
MULTI LEVEL QUEUE SCHEDULING

16. System process
Fore ground process
Background process
Student process
FOUR READY QUEUE PARTITIONS

17. The system process might be scheduled by an FCFS algorithm.
SYSTEM PROCESS

18. Foreground process is also known as interactive process.
It is might be scheduled by an short jump first algorithm.
FOREGROUND PROCESS

19. Background process is also known as batch process.
It is might be scheduled by an round robin algorithm.
BACKGROUND PROCESS

20. Student process might be scheduled by an SRJ algorithm.
STUDENT PROCESS

21. In this scheme, the ready queue is divided into number of queues.
It allows a process to move between processes.
ADVANTAGES
A process that waits too long into a lower-priority queue
may be moved to a higher priority queue.
MULTI LEVEL FEEDBACK
QUEUE SCHEDULING

22. In multi processor scheduling, each processor examines the common ready
queue and selects a process to execute.
MULTI PROCESSOR SCHEDULING