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. CPU Scheduling Algorithms are used to assign the processes to the CPU. There are various CPU Scheduling Algorithms. Practice Problems based on. Avg. Wait = 0+8+14+15+24 = 61/5 = ms Avg. TAT = 8+14+15+24+27 = ms. Shortest Job First. P5. P2. P1. P4. CPU Scheduling Exercises. Problem 1.

Author: Dolabar Meztigul
Country: Haiti
Language: English (Spanish)
Genre: Literature
Published (Last): 9 February 2018
Pages: 167
PDF File Size: 4.12 Mb
ePub File Size: 7.34 Mb
ISBN: 208-2-47012-465-9
Downloads: 92532
Price: Free* [*Free Regsitration Required]
Uploader: Nitilar

When Scheduling takes place only under circumstances 1 and 4, we say the scheduling scheme is non-preemptive ; otherwise the scheduling scheme is preemptive. The processor is allocated to the job closest to completion but it can be preempted by a newer ready job with shorter time to completion.

Whenever the CPU becomes idle, the operating system must select one of the processes in the ready queue to be executed.

What is CPU Scheduling?

Switching context Switching to user mode Jumping to the proper location in the user program to restart that program from where it left cppu time.

It is the only method that can be used on certain hardware platforms, because It does not require the special hardware for example: Operating System Scheduling algorithms Advertisements.

numerucals Once a process is executed for a given time period, it is preempted and other process executes for a given time period. To decide which process numericalx execute first and which process to execute last to achieve maximum CPU utilisation, computer scientists have defined some algorithms, they are:. Amount of time it takes from when a request was submitted until the first response is produced. The dispatcher should be as fast as possible, given that it is invoked during every process switch.

CPU Scheduling in Operating System | Studytonight

Remember, it is the time till the first response and not the completion of process execution final response. The aim of CPU scheduling is to make the system efficient, fast and fair.


Each process is assigned a priority. It is the total number of processes completed per unit time or rather say total amount of work done in a unit of time.

These algorithms are either non-preemptive or preemptive. This scheduling method is used by the Microsoft Windows 3. Dispatch Latency can be explained using the below figure: A Process Scheduler schedules different processes to be assigned to the CPU based on particular scheduling algorithms.

Operating System Scheduling algorithms

When a process switches from the running state to the ready state for example, when an interrupt occurs. In circumstances 1 and 4, there is no choice in terms of scheduling.

In this type of Scheduling, the tasks are usually assigned with priorities. The dispatcher is the module that gives control of the CPU to the process selected by the short-term scheduler. It is the average number of processes residing in the ready queue waiting for their turn to get into the CPU. Priority can be decided based on memory requirements, time requirements or any other resource requirement. Process with highest priority is to be executed first and so on.

The scheduler selects from among the processes in memory that are ready to execute, and allocates the CPU to one of them. 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.

A new process if one exists in the ready queue must be selected for execution. There is a choice, however in circumstances 2 and 3.

Another component involved in the CPU scheduling function is the Dispatcher. In general CPU utilization and Throughput are maximized and other factors cpj reduced for proper optimization. Under non-preemptive scheduling, once the CPU has been allocated to a process, the process keeps the CPU until it releases the CPU either by terminating or by switching to the waiting state.


At times it is necessary to run a certain task that has a higher nummericals before another task although it is running. The interval from time of submission of the process to the time of completion of the process Wall clock time.

There are many different criterias to check when considering the “best” scheduling algorithm, they are:. Priority scheduling is a non-preemptive algorithm and one of the most common cu algorithms in batch systems. Therefore, the running task is interrupted for some time and resumed later when the priority task has finished its execution. The selection process is carried out by the short-term scheduler or CPU scheduler. When a process terminates. We will be discussing all the scheduling algorithms, one by one, in detail wcheduling the next tutorials.

CPU Scheduling | Practice Problems | Numericals | Gate Vidyalay

Dispatch Latency can be explained using the below figure:. It is the amount of time taken to execute a particular process, i. They make use of other existing algorithms to group and schedule jobs svheduling common characteristics. Non-preemptive algorithms are designed so that once a process enters the running state, it cannot be preempted until it completes its allotted time, whereas the preemptive scheduling is based on priority where a scheduler may preempt a low priority running process anytime when a high priority process enters into a ready state.

The Process Scheduler then alternately selects jobs from each queue and assigns them to the CPU based on the algorithm assigned to the queue.

What is CPU Scheduling? The time taken by the dispatcher to stop one process and start another process is known as the Dispatch Latency. Multiple-level queues are not an independent scheduling algorithm.