Correct Answer - Option 3 : Variable scheduling
Explanation:
Scheduling is the process of deciding which task should be executed at any point in time based on a predefined algorithm. The logic for the scheduling is implemented in a functional unit called the scheduler.
There are many scheduling algorithms that can be used for scheduling task execution on a CPU. They can be classified into two main types: preemptive scheduling algorithms and non-preemptive scheduling algorithms.
1. Preemptive scheduling allows the interruption of a currently running task, so another one with more “urgent” status can be run. The interrupted task is involuntarily moved by the scheduler from running state to ready state. This dynamic switching between tasks that this algorithm employs is, in fact, a form of multitasking. It requires assigning a priority level for each task. A running task can be interrupted if a task with a higher priority enters the queue.
2. In non-preemptive scheduling, the scheduler has more restricted control over the tasks. It can only start a task and then it has to wait for the task to finish or for the task to voluntarily return the control. A running task can’t be stopped by the scheduler.
3.Cooperative scheduling: Cooperative scheduling is a style of scheduling in which the OS never interrupts a running process to initiate a context switch from one process to another. Processes must voluntarily yield control periodically or when logically blocked on a resource.
4. Fixed Time Scheduling: In this scheduling algorithm the processor makes sure that the highest priority task is to be performed first ignoring the other task to be executed.
Variable scheduling is not a type of scheduling model used by RTOS. Hence option (3) is the correct answer.
