The document discusses process scheduling in operating systems, detailing the different levels of scheduling: long-term, short-term, and medium-term, as well as various process states. It evaluates scheduling algorithms such as FCFS, SJF, Round Robin, and priority scheduling based on criteria like CPU utilization, throughput, and fairness. Additionally, it covers methods for algorithm evaluation, including deterministic modeling, queueing models, and simulations.

1. 1. Basic Concepts
Process Scheduling
 The OS manages processes using a scheduler to allocate CPU time efficiently.
 Scheduling occurs at different levels:
1. Long-term scheduling: Decides which processes enter the system.
2. Short-term scheduling: Determines which process gets CPU next.
3. Medium-term scheduling: Swaps processes in and out of memory.
Process States
1. New → Process is created.
2. Ready → Waiting for CPU.
3. Running → Executing on CPU.
4. Waiting → Blocked for I/O or resource.
5. Terminated → Finished execution.
CPU Scheduler
 Chooses from the ready queue and assigns a process to the CPU.
 Uses scheduling algorithms to decide which process to run.
2. Scheduling Criteria
Used to evaluate scheduling algorithms:
1. CPU Utilization → Keep CPU as busy as possible (goal: 40-90%).
2. Throughput → Number of processes completed per unit time.
3. Turnaround Time → Time from process submission to completion.
4. Waiting Time → Time spent in the ready queue.

2. 5. Response Time → Time from request submission to first response.
6. Fairness → Equal distribution of CPU time among processes.
Goal: Minimize turnaround, waiting, and response times while maximizing CPU utilization and
throughput.
3. Scheduling Algorithms
1. First-Come, First-Served (FCFS)
 Non-preemptive, simple queue-based.
 Pros: Fair, easy to implement.
 Cons: Long wait time for short processes (convoy effect).
2. Shortest Job Next (SJN) / Shortest Job First (SJF)
 Picks the process with the shortest burst time.
 Non-preemptive or preemptive (SRTF - Shortest Remaining Time First).
 Pros: Optimal for minimizing waiting time.
 Cons: Hard to predict burst time, starvation for longer jobs.
3. Round Robin (RR)
 Preemptive, each process gets a fixed time quantum.
 Pros: Fair for time-sharing, responsive.
 Cons: High context-switching overhead.
4. Priority Scheduling
 Assigns a priority to each process.
 Non-preemptive or preemptive.
 Pros: Prioritizes important tasks.

3.  Cons: Starvation (solved by aging).
5. Multilevel Queue Scheduling
 Separates processes into queues (e.g., system, user, background).
 Each queue has its own scheduling algorithm.
 Pros: Good for different user needs.
 Cons: Complex implementation.
6. Multilevel Feedback Queue Scheduling
 Dynamic priority adjustment (processes can move between queues).
 Pros: Adaptive, prevents starvation.
 Cons: More complex than fixed-priority queues.
4. Algorithm Evaluation
1. Deterministic Modeling
 Uses predefined workloads to compare performance.
 Example: Compare FCFS vs. SJF for known processes.
2. Queueing Models
 Uses mathematical models to predict scheduling behavior.
 Based on arrival rates, service time, etc.
3. Simulations
 Generates random workloads and measures algorithm performance.
4. Implementation & Testing

4.  Real-world deployment to analyze performance under actual conditions.