In operating system process scheduling, what is the CPU scheduler and what is its main function?

Introduction / Context:
Modern operating systems allow many processes and threads to share a single CPU. The system needs a mechanism to decide which process runs at any given moment. This decision is handled by the CPU scheduler, an essential part of process management. Understanding its role is key to analyzing response time, throughput, and fairness in a multitasking system.

Given Data / Assumptions:

• There are one or more CPUs and many runnable processes or threads.
• Processes move between states such as running, ready, and blocked.
• The operating system uses a scheduling algorithm such as round robin, priority, or shortest job first.

Concept / Approach:
The CPU scheduler is the operating system component responsible for choosing which process or thread in the ready state should be dispatched to run on the CPU next. It implements a scheduling policy that may consider priorities, time slices, waiting time, and other factors. Short term scheduling decisions happen frequently, often on every timer interrupt, I or O completion, or system call that yields the CPU. The scheduler aims to balance CPU utilization, throughput, turnaround time, response time, and fairness.

Step-by-Step Solution:
Step 1: Recognize that the CPU is a shared resource that cannot run all ready processes simultaneously unless there are multiple cores.Step 2: Understand that the CPU scheduler maintains a ready queue of processes that are eligible to run.Step 3: On certain events, the scheduler selects one process from this ready queue according to the scheduling policy.Step 4: The dispatcher then performs a context switch and hands the CPU to the chosen process.Step 5: Select the option that describes this role of choosing the next process for CPU execution.

Verification / Alternative check:
Textbooks describe three levels of scheduling: long term job scheduling, medium term swapping scheduling, and short term CPU scheduling. The term CPU scheduler usually refers to the short term scheduler that makes frequent decisions about which ready process runs next. Tools like top or task manager show the result of scheduling decisions as different processes get CPU time. These observations fit the definition in the correct option.

Why Other Options Are Wrong:
Option B: Describes a hypothetical hardware device that speeds up the CPU, which is not what the scheduler does.Option C: Refers to a user application that controls the system clock manually, which is unrelated to process scheduling.Option D: Talks about a disk defragmentation scheduler, which is a utility specific function and not the core CPU scheduling component.

Common Pitfalls:
Students sometimes confuse the CPU scheduler with the dispatcher. The scheduler decides which process should run, while the dispatcher performs the low level context switch. Another confusion is between long term job scheduling, which controls system load, and short term CPU scheduling, which controls immediate CPU allocation. Exam questions often focus on the short term scheduler.

Final Answer:
The correct answer is A component of the operating system that selects which ready process or thread should be given the CPU next according to a scheduling policy.