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Q.

A scheduling algorithm assigns priority proportional to the waiting time of a process. Every process starts with priority zero (the lowest priority). The scheduler re-evaluates the process priorities every T time units and decides the next process to schedule. Which one of the following is TRUE if the processes have no I/O operations and all arrive at time zero?

A This algorithm is equivalent to the first-come-first-serve algorithm.
B This algorithm is equivalent to the round-robin algorithm.
C This algorithm is equivalent to the shortest-job-first algorithm.
D This algorithm is equivalent to the shortest-remaining-time-first algorithm.

Answer & Explanation

Answer: Option [B]

A scheduling algorithm assigns priority proportional to the waiting time of a process.

In case of option [A] i.e. FCFS scheduling algorithm, processes are executed one by one according to their arrival time in the ready queue. There is no role of priority in FCFS scheduling. So it rejected.

In case of option [B] i.e. Round robin scheduling is similar to FCFS algorithm but preemptive round robin scheduling is different. Switching between processes is possible in preemptive round robin scheduling. A small unit of time slice or time quantum is assigned to each processes and they are executed one by one in a circular queue or ready queue.

In case of option [C] i.e. the process with shortest next CPU burst will be executed. So it is rejected.

In case of option [D] i.e. the process with shortest remaining run time will be executed. So it is also rejected.

Given that all processes are arrived at time zero. So the waiting time of each process is zero. Any of the processes is executed. The priority is increases when the waiting time is increases. So we can conclude that preemptive round robin scheduling is the right answer.

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