Sem-3, BCA, SYSTEM SOFTWARE AND OPERATING SYSTEM, Unit-7, CPU Scheduling

1 IDOL Institute of Distance and Online Learning ENHANCE YOUR QUALIFICATION, ADVANCE YOUR CAREER. www.cuidol.in Unit-1(BCA134) All right are reserved with CU-IDOL

BCA 2 All right are reserved with CU-IDOL SYSTEM SOFTWARE AND OPERATING SYSTEM ❑Course Code: BCA134 ❑Semester: Third ❑e-Lesson: 7 ❑SLM Unit: 7 www.cuidol.in Unit-1(BCA134)

SYSTEM SOFTWARE AND OPERATING SYSTEM 33 OBJECTIVES INTRODUCTION Describe the utility of different system An operating system is a programs & system tools. program that controls the execution of application To understand evolution, types and programs and acts as an functions of OS. interface between the user of a computer and the computer Participants will be able to learn about hardware. Scheduling policies, process concurrency, I/O management, and File systems. INSTITUTE OF DISTANACEll ArNigDhOt aNrLeINreEsLeErAvReNdIwNGith CU-IDOL . Unit-1(BCA134) www.cuidol.in

TOPICS TO BE COVERED 4 ❖ CPU Scheduling Human Respurce Manageemnet www.cuidol.in Unit-1(BCA134) All right are reserved with CU-IDOL

CPU Scheduling 5 • CPU scheduling is a process which allows one process to use the CPU while the execution of another process is on hold(in waiting state) due to unavailability of any resource like I/O etc, thereby making full use of CPU. • The aim of CPU scheduling is to make the system efficient, fast and fair. www.cuidol.in Unit-1(BCA134) All right are reserved with CU-IDOL

Scheduling Criteria 6 All right are reserved with CU-IDOL CPU utilization Throughput Turn around time Waiting Time Load Average Response Time www.cuidol.in Unit-1(BCA134)

Scheduling Criteria 7 • CPU Utilization:-It is the average fraction of time during which the processor is busy. • Throughput:-It is the total number of processes completed per unit time or rather say total amount of work done in a unit of time. • Turnaround time:-It is the amount of time taken to execute a particular process, i.e. The interval from time of submission of the process to the time of completion of the process. • Waiting time:-The sum of the periods spent waiting in the ready queue amount of time a process has been waiting in the ready queue to acquire get control on the CPU. www.cuidol.in Unit-1(BCA134) All right are reserved with CU-IDOL

Scheduling Criteria 8 • Load average:-It is the average number of processes residing in the ready queue waiting for their turn to get into the CPU. • Response time:-Amount of time it takes from when a request was submitted until the first response is produced. Remember, it is the time till the first response and not the completion of process execution(final response). www.cuidol.in Unit-1(BCA134) All right are reserved with CU-IDOL

Types Of Scheduling 9 Scheduling algorithms are of two types: 1. Preemptive Algorithms 2. Non-Preemptive Algorithms • Non preemptive Scheduling:-A scheduling discipline is non preemptive if, once a process has been given the CPU, the CPU cannot be taken away from that process. • Preemptive Scheduling:-A scheduling discipline is preemptive if, once a process has been given the CPU can taken away. www.cuidol.in Unit-1(BCA134) All right are reserved with CU-IDOL

Scheduling Algorithms 10 • First Come First Serve(FCFS) Scheduling • Shortest-Job-First(SJF) Scheduling • Priority Scheduling • Round Robin(RR) Scheduling • Multi-Processor Scheduling www.cuidol.in Unit-1(BCA134) All right are reserved with CU-IDOL

First Come First Serve(FCFS) 11 • Jobs are executed on first come, first serve basis. • Easy to understand and implement. • Poor in performance as average wait time is high. Advantages: • .IT is simple to understand and easy to implement. • Suitable for batch system • It follows the principle of First come first served. • No starvation Disadvantages: • This scheduling method is non-preemptive , the process runs until it finishes. • Not suitable for time sharing system www.cuidol.in Unit-1(BCA134) All right are reserved with CU-IDOL

Shortest Job First (SJF) 12 • In Preemptive Shortest Job First Scheduling, jobs are put into ready queue as they arrive, but as a process with short burst time arrives, the existing process is preempted. Advantage: • It gives minimum average waiting time for a given set of processes. By moving a short process before a long process, the waiting time of the short process decreases more than it increases the waiting time of the long process. Disadvantage: • It requires precise knowledge of how long a job or process will run and this information is usually not available. www.cuidol.in Unit-1(BCA134) All right are reserved with CU-IDOL

Priority Scheduling 13 • Priority is assigned for each process. • Process with highest priority is executed first and so on. • Processes with same priority are executed in FCFS manner. • Priority can be decided based on memory requirements, time requirements or any other resource requirement. Advantages: • Good response for higher priority processes Disadvantages: • Indefinite blocking for lower priority processes. www.cuidol.in Unit-1(BCA134) All right are reserved with CU-IDOL

Round Robin Scheduling(RR) 14 • Time sharing system used the round robin algorithm. • Use of small quantum allows round robin to provide good response time. • RR algorithm is preemptive algorithm. • To implement RR scheduling ready queue is maintained as FCFS. New processes will be added to the tail of the queue.. The CPU scheduler picks the first process from the queue, sets the timer to interrupt after 1 time quantum and dispatches the process. With RR algorithm, Principal design issue is length if time quantum. www.cuidol.in Unit-1(BCA134) All right are reserved with CU-IDOL

Multiprocessor Scheduling 15 • More than one processor is there.. • Load sharing • Processes are not assigned to a particular processor. • A global queue of ready threads is maintained • Each processor when idle select a thread from the queue. www.cuidol.in Unit-1(BCA134) All right are reserved with CU-IDOL

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