Question

What do these acronyms mean: LPT, FCFS and SPT? Which is usually the best, and how would defend your answer?

Answer 1

LPT = Longest processing time

It represents how we arrange the jobs to be executed based on the longest/time-intensive jobs to be scheduled first.

FCFS = first come first serve

It represents jobs performed in the order they are received. Depending on the task, the arrangement can be either good or bad but following this rule would mean that task A received first will be performed first.

SPT = shortest processing time

Similarly, jobs are performed based on the tasks taking the least amount of time to be conducted first.

2. We can say that the entire reason for different rules to exist itself provides an understanding that no one rule is the best. For example, in first come first serve, the tasks that are assigned based on the order they are received would mean that while a task with longer time will take longer to be finished, based on the due time, shorter tasks could result in a larger slack and therefore, wasted resources. On the other hand, let’s say there are three jobs A, B, and C, we are using first come first serve heuristic. We will perform first A, then B and then C. However, the due time for job C is earlier than job B or job A. Therefore, while A and B would be finished in time, C would be late. Same is true for all the other heuristics as well.

Statistically, however, EDD rule where the job with the earliest due date is performed first has been shown to be slightly more effective, especially in N/1 scenario.

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