When using FPS, once priorities are assigned to tasks they are not changed.
Then, during execution,the task with the highest priority among all tasks that are available for execution is scheduled for exe-cution.
Priorities can be assigned in many ways, and depending on the system requirements some priority assignments are better than others.
In RM, the priority is assigned based on the period of the task. The shorter the period, the higher will be the priority assigned to the task.