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CPU Scheduling Algorithms: Optimizing Process Execution and Resource Allocation

Explore various CPU scheduling algorithms (FCFS, Round Robin, SJF, etc.) used in operating systems to manage process execution and resource allocation. This tutorial compares their performance characteristics, advantages, disadvantages, and suitability for different system workloads, providing a comprehensive understanding of CPU scheduling.

CPU Scheduling Algorithms in Operating Systems

Goals of CPU Scheduling

CPU scheduling algorithms aim to optimize the allocation of CPU time to processes, balancing various competing goals. Effective scheduling is critical for maximizing system performance and ensuring fairness among processes.

  • Maximize CPU utilization (minimize idle time).
  • Ensure fair allocation of CPU time to all processes.
  • Maximize throughput (number of processes completed per unit of time).
  • Minimize turnaround time (time from submission to completion).
  • Minimize waiting time (time a process spends in the ready queue).
  • Minimize response time (time from request to first response).

Common CPU Scheduling Algorithms

Several algorithms are used for CPU scheduling, each with its strengths and weaknesses:

1. First-Come, First-Served (FCFS):

This is the simplest algorithm. Processes are scheduled in the order they arrive. It's non-preemptive (a running process runs to completion). Simple to implement, but can be inefficient if long jobs arrive early.

2. Round Robin:

A time quantum (time slice) is assigned to each process. Processes are scheduled in a circular manner. If a process doesn't finish within its time quantum, it goes back to the ready queue and waits. This is a preemptive algorithm (a running process can be interrupted).

3. Shortest Job First (SJF):

The process with the shortest burst time (CPU execution time) gets scheduled first. This minimizes average waiting time. It's non-preemptive. Requires knowledge of burst times (which is difficult to predict accurately).

4. Shortest Remaining Time First (SRTF):

The preemptive version of SJF. The process with the shortest remaining burst time gets scheduled next. A running process can be preempted if a higher-priority (shorter remaining time) process arrives.

5. Priority-Based Scheduling:

Each process is assigned a priority. Higher-priority processes are scheduled first. Processes with the same priority are scheduled based on arrival time. Priority can be assigned based on various factors.

6. Highest Response Ratio Next (HRRN):

A preemptive priority scheduling algorithm that considers both waiting time and burst time to assign priorities. This helps to reduce starvation of longer jobs.