Mar 24 2020

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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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. Dispatch Latency can be explained using the below figure:.

Operating System Scheduling algorithms

The interval from time of submission of the process to the time of completion of the process Wall clock time. 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? It is the only method that can be used on certain hardware platforms, because It does not require the special hardware for example: Amount of time it takes from when a request was submitted until the first response is produced.

Operating System Scheduling algorithms

Therefore, the running task is interrupted for some time and resumed later when the priority task has finished its execution. Operating System Scheduling algorithms Advertisements. The scheduler selects from among the processes in memory that are ready to execute, and allocates the CPU to one of them.


Each process is assigned a priority. 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:. In circumstances 1 and 4, there scheeduling no choice in terms of scheduling. Process with highest priority is to be executed first and so on. There are many different criterias to check when considering the “best” scheduling algorithm, they are:.

When a process switches from the running state to the ready state for example, when an interrupt occurs.

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.

A new process if one exists in the ready queue must be selected for execution.

What is CPU Scheduling?

It is the total number of processes completed per unit time or rather say total amount of work done in a unit of time. They make use of other existing algorithms to group and schedule jobs with common characteristics. The dispatcher is the module that gives control of the CPU to the process selected by the short-term scheduler.

A Process Scheduler schedules different processes to be assigned to the CPU based on particular scheduling algorithms. In general CPU utilization and Throughput are maximized and other factors are reduced for proper optimization.

The time taken by the dispatcher to stop one process and start another process is known as the Dispatch Latency. In this type of Scheduling, the tasks are usually assigned with priorities.


Multiple-level numsricals are not an independent scheduling algorithm. 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.

Whenever the CPU becomes idle, the operating system must select one of the processes in the ready queue to be executed. Once a process is executed for a given time period, it is preempted and other process executes for a given time period.

This scheduling method is used by the Microsoft Windows 3. There is a choice, however in circumstances 2 and 3.

CPU Scheduling | Practice Problems | Numericals | Gate Vidyalay

Priority can be decided based on memory requirements, time requirements or any other resource requirement. The selection process is carried out by the short-term scheduler or CPU scheduler. Dispatch Latency can be explained using the below figure: The aim of CPU scheduling is to make the system efficient, fast and fair. Another component involved in the CPU scheduling function is the Dispatcher. 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 amount of time taken to execute a particular process, i.