Question

operating system

(5 points) Explain the primary reason that it is hard to implement a Shortest Job First algorithm in a real-world system.

Answer 1

Shortest Job First Algorithm:

Shortest Job First algorithm is a CPU scheduling algorithm, in which the process which has the smallest burst time is allocated to the CPU first. If the burst time of the two processes is the same then the First Come First Serve algorithm is used to break the tie. This algorithm provides minimum waiting time and maximum throughput.

The primary reason that makes the implementation so hard is to calculate the burst time.

Before the process execution, we don't know how much burst time the process will take in execution exactly. We calculate the approximate value of the burst time. If our approximate value calculation method doesn't work correctly then the performance of the system will decrease.

We calculate the burst time on the basis of the process which has already executed. So, this algorithm works on the predicted burst time but not on actual burst time.

We can calculate the burst time by two methods:

1. Static method
2. Dynamic method

The static method is not so reliable because its prediction is not correct always. So, we use the dynamic method for burst time prediction.