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.

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Multiple-level queues are not an independent scheduling algorithm.

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 schedulling a high priority process enters into a ready state.

In this type of Scheduling, the tasks are usually assigned with priorities. There are many different criterias to check when considering the “best” scheduling algorithm, they are:. Dispatch Latency can be explained using the below figure: Zcheduling interval from time of submission of the process to the time of completion of the process Wall clock time.

The sum of the periods spent waiting in the ready queue amount of time a process has schedullng waiting in the ready queue to acquire get control on the CPU.

scheuling The selection process is carried out by the short-term scheduler or CPU scheduler. Another component involved in the CPU scheduling function is the Dispatcher.


Priority can be decided based on memory requirements, time requirements or any other resource requirement.

Operating System Scheduling algorithms

These algorithms are either non-preemptive or preemptive. It is the only method that can be used on certain hardware platforms, because It does not require the special hardware for example: Dispatch Latency can be explained using the below figure:.

Remember, it is the time till the first response and not the completion of process execution final response. A new process if one exists in the ready queue must be selected for execution. In circumstances 1 and 4, there is no choice in terms of scheduling.

What is CPU Scheduling?

There is a choice, however in circumstances 2 and 3. Amount of time it takes from when a request was submitted until the first response is produced. At times it is necessary to run nymericals certain task that schedulng a higher priority before another task although it is running.

To decide which process to execute first and which process to execute last to achieve maximum CPU utilisation, computer scientists have defined some algorithms, they are:.

Priority scheduling is a non-preemptive algorithm and one of the most common scheduling algorithms in numegicals systems. Whenever the CPU becomes idle, the operating system must select one of the processes in the ready queue to be executed. Operating System Scheduling algorithms Advertisements.

CPU Scheduling in Operating System | Studytonight

The scheduler selects from among the processes in memory that are ready to execute, and allocates the CPU to one of them. The Process Schedulinv then alternately selects jobs from numerocals queue and assigns them to the CPU based on the algorithm assigned to the queue.


They make use of other existing algorithms to group and schedule jobs with common characteristics. 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.

Each process is assigned a priority. When Scheduling takes place only under circumstances 1 and 4, we say the scheduling scheme is non-preemptive ; otherwise the scheduling scheme is preemptive. It is the average number of processes residing in the ready queue waiting for their turn to get into the CPU. The dispatcher is the module that gives control of the CPU to the process selected by the short-term scheduler.

This scheduling method is used by the Microsoft Windows 3. It is the amount of time taken to execute a particular process, i. The time taken by the dispatcher to stop one process and start another process is known as the Dispatch Latency. Process with highest priority is to be executed first and so on. Once a process is executed for a given time period, it is preempted and other process executes for a given time period.