Define scheduler an explain the types of the scheduler(OS-5)

Scheduler 

-Scheduler is the special system software which handle the process scheduling in various ways. Their the main tasks is to select the jobs to be submitted into the system and to decide with process to run.

-There are three types of scheduler:

                                                        1.long term scheduler

                                                        2.medium term scheduler

                                                        3.short term scheduler 

Long term scheduler:

-It is also known as job scheduler. The function of the long term scheduler is to select the job from the pull of the jobs and loaded the jobs in the main memory called ready queue of the computer. So long term scheduler is known as job scheduler.

-Ready queue is a data structure in which the data is entered in the queue first will be entire ed so it is a FIFO structure.

-Queue has a two ends first one is rear and second one is front.

-The jobs are loaded into the ready queue throw the rear end and detect throw the front end .

-So the long term scheduler is to select the job from disk and loaded these jobs into ready queue in the main memory.

-The long term scheduler is switch the state from new-ready.

Medium term scheduler :

-If a request an I/O operation in the middle of into execution then the medium term scheduler removed that process from main  memory and loaded it into waiting queue that is medium term scheduler can change the process state from running to waiting.

-When the I/O operation of that job is completed then the medium term scheduler removed that process one job from waiting queue and loaded it again in the ready queue.

-So it is responsible can change process state from waiting to ready.

Short term scheduler:

-The function of the short term scheduler is to select the job from ready queue and give the control in the CPU to that job with the help of another program module dispatcher.

-This is the reason for which short term scheduler is called CPU scheduler.

-The method of the selecting process from ready queue by the short term scheduler depending on the CPU scheduling so the short term scheduler can change the process state from ready to running.