a) The usual scheduling algorithms for each mentioned queue in multilevel queue scheduling are:
- Foreground Queue: The foreground queue typically uses a CPU-bound scheduling algorithm, such as Round Robin (RR) or Shortest Job Next (SJN), to prioritize processes that require immediate attention or have higher priority.
- Background Queue: The background queue typically uses an I/O-bound scheduling algorithm, such as First-Come, First-Served (FCFS) or Priority Scheduling, to prioritize processes that are less time-sensitive and can run in the background.
b) In multilevel queue scheduling, the scheduling between the queues is typically done based on priority or a predefined scheduling algorithm. The goal is to ensure fairness and efficiency in utilizing system resources.
There are different approaches to scheduling between the queues:
- Fixed Priority: Each queue is assigned a fixed priority, and the scheduler selects the highest priority queue that has ready processes. This approach ensures that higher-priority tasks are executed first, allowing for real-time or critical processes to be prioritized over less important ones.
- Time Slicing: Each queue is assigned a specific time quantum, and the scheduler switches between the queues after each time quantum expires. This approach ensures that each queue gets a fair share of CPU time and prevents starvation of lower-priority processes.
- Feedback Scheduling: In this approach, the scheduler dynamically adjusts the priority or queue assignment of a process based on its behavior and resource requirements. For example, if a process in the foreground queue becomes I/O-bound, it can be moved to the background queue to free up CPU resources.
The specific scheduling mechanism between the queues depends on the operating system's design and the requirements of the system. The goal is to achieve a balance between responsiveness, fairness, and resource utilization based on the characteristics of the processes in each queue.