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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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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:.

These algorithms are either non-preemptive or preemptive.

The sum of the periods spent waiting in the ready queue amount of time a process has been waiting in the ready queue to sccheduling get control on the CPU. Non-preemptive algorithms are designed so that once a process enters the running state, it cannot be preempted until it completes its allotted cu, 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.

Operating System Scheduling algorithms

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.

A new process if one exists in the ready queue must be selected for execution. Once a process is executed for a given time period, numerivals is preempted and other process executes for a given time period. The dispatcher should be as fast as possible, given that it is cup during every process switch. It is the average number of processes residing in the ready queue waiting for their turn to get into the CPU.


Operating System Scheduling algorithms

Process with highest priority is to be executed first and so on. Priority can be decided based on memory requirements, time requirements or any other resource requirement.

At times it is necessary to run a certain task that has a higher priority before another task although it is running. We will be discussing all the scheduling algorithms, one by one, in detail in the next tutorials.

The dispatcher is the module that gives control of the CPU to the process selected by the short-term scheduler. In circumstances 1 and 4, there is no choice in terms of scheduling. Switching context Switching to user mode Jumping to the proper location in the user program to restart that program from where it left last time. The scheduler selects from among the processes in memory that are ready to execute, and allocates the CPU to one of them.

The interval from time of submission of the process to the time of completion of the process Wall clock time.

Dispatch Latency can be explained using the below figure:. When a process terminates. Dispatch Latency can be explained using the below figure: In general CPU utilization and Throughput are maximized and other factors are reduced for proper optimization. Therefore, the running task is interrupted for some time and resumed later when the priority task has finished its execution. The aim of CPU scheduling is to make the system efficient, fast and fair.


They make use of other existing algorithms to group and schedule jobs with common characteristics. Remember, it is the time till the first response and not the completion of process execution final response.

It is the amount of time taken to execute a particular process, i.

What is CPU Scheduling?

This scheduling method is used by the Microsoft Windows 3. When a process switches from the running state to the ready state for example, when an interrupt occurs.

Whenever the CPU becomes idle, the operating system must select one of the processes in the ready queue to be executed. Multiple-level queues are not an independent scheduling algorithm.

There are many different criterias to check when considering the “best” scheduling algorithm, they are:.

What is CPU Scheduling? The time taken by the dispatcher to stop one process and start another process is known as the Dispatch Latency. There is a choice, however in circumstances 2 and 3.

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