Short Answer
CPU scheduling is the process used by the operating system to decide which process will use the CPU at a given time. Since many processes compete for CPU time, scheduling ensures fair and efficient use of the processor.
It improves system performance by managing process execution in an organized way. The CPU scheduler selects processes from the ready queue and assigns CPU time based on scheduling algorithms.
Detailed Explanation:
CPU Scheduling Overview
Definition:
CPU scheduling is a function of the operating system that manages the selection of processes waiting in the ready queue and allocates CPU time to them. Since a computer system runs multiple processes at the same time, the CPU cannot execute all processes simultaneously. Therefore, scheduling is required to decide the order of execution.
Importance of CPU Scheduling:
CPU scheduling is very important because it improves system efficiency, reduces waiting time, and increases CPU utilization. Without scheduling, some processes may wait too long, while others may use too much CPU time. Scheduling ensures fairness and smooth execution of all processes.
Process of CPU Scheduling
Ready Queue
Meaning:
The ready queue is a list of all processes that are ready to execute but are waiting for CPU time.
Explanation:
When a process is created and ready for execution, it is placed in the ready queue. The CPU scheduler selects processes from this queue based on a scheduling algorithm.
CPU Scheduler
Meaning:
The CPU scheduler is a part of the operating system that selects the next process to execute.
Explanation:
It decides which process should get CPU time next. The selection is based on factors like priority, waiting time, and scheduling method.
Dispatching
Meaning:
Dispatching is the process of giving CPU control to the selected process.
Explanation:
After the scheduler selects a process, the dispatcher loads its state into the CPU so that execution can begin. This includes switching context from one process to another.
Types of CPU Scheduling
Preemptive Scheduling
Meaning:
In preemptive scheduling, the CPU can be taken away from a running process.
Explanation:
If a higher priority process arrives, the current process is stopped temporarily, and the new process is executed.
Example:
Round Robin and Priority Scheduling.
Non-Preemptive Scheduling
Meaning:
In non-preemptive scheduling, once a process starts execution, it cannot be stopped until it finishes.
Explanation:
The CPU is assigned to a process until it completes or enters waiting state.
Example:
First Come First Serve (FCFS) and Shortest Job First (SJF).
CPU Scheduling Algorithms
First Come First Serve (FCFS)
Meaning:
Processes are executed in the order they arrive.
Explanation:
The first process in the queue gets executed first. It is simple but may cause long waiting time.
Shortest Job First (SJF)
Meaning:
The process with the shortest execution time is selected first.
Explanation:
It reduces average waiting time but requires knowledge of process length.
Round Robin
Meaning:
Each process gets a fixed time slot called time quantum.
Explanation:
After the time is over, the process goes back to the queue if not finished. It is widely used in time-sharing systems.
Priority Scheduling
Meaning:
Each process is assigned a priority level.
Explanation:
Higher priority processes are executed first. If priorities are equal, FCFS is used.
Advantages of CPU Scheduling
Efficient CPU Use:
CPU remains active and does not stay idle.
Fairness:
All processes get a chance to execute.
Better Performance:
Reduces waiting time and improves system speed.
Multitasking Support:
Allows multiple processes to run efficiently.
Disadvantages of CPU Scheduling
Complex System:
Scheduling algorithms make the system more complex.
Overhead:
Frequent switching between processes can reduce performance.
Conclusion
CPU scheduling is an important function of the operating system that manages process execution in a computer system. It ensures that the CPU is used efficiently by selecting processes from the ready queue using scheduling algorithms. This improves performance, fairness, and multitasking ability of the system.