Shortest Job First, explained.
Shortest-job-first orders available jobs by processing duration and minimises total completion time in the basic single-server setting with all jobs available initially.
Why it happens
Five durations eight, two, six, one and three share arrival time zero. A player-built order or two presets produce exact start and completion ledgers; every complete non-idling schedule finishes at time twenty.
Shortest-job-first orders available jobs by processing duration and minimises total completion time in the basic single-server setting with all jobs available initially.
Read the result
Compare average waits only across complete schedules of the same five jobs. Partial-schedule averages reflect different job subsets.
A worked example
Reduce average waiting without changing final completion
Use arrival order for durations eight, two, six, one and three; inspect the waiting ledger.
Switch to shortest-job-first order D, B, E, C, A and compare mean wait falling from 10.2 to 4.4.
Observe that both complete non-idling schedules still finish at time twenty, separating makespan from mean waiting.
OPTIONAL DEEPER DETAILGo deeper: inside the model
Inside this model
Five durations eight, two, six, one and three share arrival time zero. A player-built order or two presets produce exact start and completion ledgers; every complete non-idling schedule finishes at time twenty.
Where this idea is useful
A practical use
Separate minimising the final completion time from reducing the average time individual jobs wait.
A common misconception
“Finishing the final job at the same time makes all schedules equivalent.”
Different orders redistribute completion and waiting times among jobs even when total processing work and makespan stay fixed.
What this explanation leaves out
- Known durations, equal priorities, simultaneous arrivals and nonpreemption are assumed. Changing arrivals, deadlines, fairness and starvation can require another scheduling objective.
Does shortest-job-first solve fairness for an ongoing queue?
No. Unknown durations, changing arrivals, priorities and starvation concerns introduce objectives absent from the simultaneous-arrival toy.
Whose waiting time changes when you reorder work without changing its total duration?
Associated thinkers
Associations marked provisional are awaiting source review.
Further reading
Explore the original research or the teaching reference behind this experiment.