Scheduling

*Process Scheduling*

Process scheduling is the allocation of CPU time to processes. The OS scheduler selects a process from the ready queue and allocates the CPU to execute it.

*Scheduling Algorithms*

1. *First-Come-First-Served (FCFS)*: Processes are executed in the order they arrive in the ready queue.

2. *Shortest Job First (SJF)*: The shortest process is executed first.

3. *Priority Scheduling*: Processes are executed based on priority, with higher-priority processes running first.

4. *Round-Robin (RR)*: Each process is allocated a fixed time slice (time quantum) in a cyclic order.

5. *Multilevel Feedback Queue (MFQ)*: Multiple queues with different priorities; processes move between queues based on their behavior.

*Scheduling Criteria*

1. *CPU Utilization*: Maximize CPU usage to minimize idle time.

2. *Throughput*: Maximize the number of processes completed per unit time.

3. *Turnaround Time*: Minimize the time between process submission and completion.

4. *Response Time*: Minimize the time between process submission and first response.

5. *Fairness*: Ensure equal allocation of resources to processes.

*Scheduling Types*

1. *Preemptive Scheduling*: The OS can suspend a running process to allocate the CPU to another process.

2. *Non-Preemptive Scheduling*: The OS cannot suspend a running process; it must complete before another process runs.

*Scheduling Data Structures*

1. *Ready Queue*: Holds processes waiting for CPU allocation.

2. *Waiting Queue*: Holds processes waiting for I/O or other resources.

3. *Zombie Process*: A process that has completed execution but still holds system resources.

*Context Switching*

Context switching occurs when the OS switches the CPU from one process to another. It involves saving the current process's state and restoring the new process's state.