Processes Scheduling queue





As processes enter the system they put in job queue. This queue consists of all processes of the system, some process is kept on main memory waiting or ready to execute, so they are placed in the list called ready queue.
So, each operating system consists of other queues when the process is allocated on its CPU. It executes for a while and eventually quite, is interrupted or waits for some particular events to occur such as I/O request I/O request is dedicated to tape driver or sharing device or disk. As we know that system comparing of number of process. The disk may be busy with I/O request of some other process. So, in that case the process has to wait for a disk, such process waiting for particular I/O device is placed in queues called I/O queue.
A common representation of process scheduling is the queuing diagram. The rectangular box represents the queue. The circle represents the resource.

processes scheduling quee

processes scheduling quee

New process always is put in ready queue. It unit in the ready queue until it is selected for execution. Once it is allocated to CPU is starts executing. The several events may occur.
1. A process may issue I/O request then be placed in I/O queue.
2. A process may create a sub process and wait for its termination.
3. A process may be interrupted in between and put back in ready queue. The process continues this cycle until if terminates.



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