In CPU scheduling algorithms, round robin scheduling falls under which general category?

Introduction / Context:
Operating systems use CPU scheduling algorithms to decide which process runs at any given time. One well known algorithm is round robin scheduling, which is often used in time sharing systems because it gives each process a fair share of the CPU. Understanding whether this algorithm is preemptive or non preemptive is a key concept in operating systems courses. This question asks you to classify round robin scheduling into the correct category.

Given Data / Assumptions:

• The scheduling algorithm in question is round robin.
• Options include preemptive scheduling, non preemptive scheduling, both, and none of the above.
• We assume a standard definition where each process receives a fixed time quantum.
• Preemption means the scheduler can interrupt a running process before it finishes its CPU burst.

Concept / Approach:
Round robin scheduling works by maintaining a circular queue of ready processes. Each process receives a fixed amount of CPU time called a time quantum. When a process's time quantum expires and it has not finished execution, the operating system preempts it and moves it to the back of the ready queue. Then the CPU is given to the next process. This behaviour requires preemption, because the system forcibly takes the CPU away from the current process when the time slice ends. Non preemptive scheduling, on the other hand, allows a process to keep the CPU until it blocks or terminates. Therefore, round robin scheduling is a preemptive scheduling algorithm.

Step-by-Step Solution:
Step 1: Recall the definition of preemptive scheduling. In preemptive scheduling, the operating system can interrupt a running process and switch the CPU to another process. Step 2: Recall how round robin operates. Each process gets a fixed time quantum; when the time is over, the scheduler preempts the process and moves to the next one. Step 3: Compare with non preemptive scheduling. In non preemptive scheduling, once a process starts, it continues on the CPU until it finishes or voluntarily yields the CPU. Step 4: Determine which category matches round robin. Because round robin relies on time based preemption, it clearly belongs to preemptive scheduling. Step 5: Eliminate options that conflict with this definition.

Verification / Alternative check:
Operating system textbooks classify scheduling algorithms and consistently list round robin under preemptive algorithms alongside priority based preemptive methods. They describe that the CPU is taken away from a process when its time slice expires, regardless of whether it is ready to continue. Descriptions of non preemptive algorithms mention first come first served and non preemptive priority, where the running process is not interrupted. There is no mention of round robin functioning without preemption. This confirms that round robin is exclusively a preemptive scheduling algorithm.

Why Other Options Are Wrong:
Option B (Non preemptive scheduling): Non preemptive algorithms do not forcibly interrupt a running process, which contradicts the time quantum behaviour of round robin. Option C (Both A & B): An algorithm cannot be both preemptive and non preemptive under the standard definitions; round robin clearly relies on preemption. Option D (None of the above): Incorrect because preemptive scheduling is a well defined category that fits round robin.

Common Pitfalls:
Some students confuse round robin with time slicing in a cooperative multitasking environment and think the process voluntarily yields the CPU, which would be non preemptive. However, in round robin, the scheduler enforces a time limit and preempts the process when the quantum expires, whether or not the process is ready to yield. Another pitfall is to believe that fairness automatically implies non preemptive behaviour, when in fact round robin's fairness comes from regular preemption. To answer correctly, always associate round robin with time quantum based preemptive scheduling.

Final Answer:
Round robin scheduling falls under the category of Preemptive scheduling because the CPU is taken away from a process when its time quantum expires.