Scheduling n Jobs × 1 Machine

Suppose there are five production departments from which five different requisitions have come to plant engineer for repairing of their machines. It is now the turn of the engineer to decide the order of these jobs and allocate to his man. If only one operator is there to perform these five jobs it becomes further critical and crucial. He can adopt one of the following methods in such situations.

 First In First Out (FIFO) or First Come First Serve

When the jobs do not require any preferential treatment this rule is considered. Repair complaints at telecom department, electricity departments usually follow such principle.

Last In First Out (LIFO)

When a machine is being opened for repair or overhaul, the parts are put back in LIFO system. However, pipeline laying in water works, electrical wiring maintenance system will follow this model.

Earliest Due Date (EDD)

Most of the times the production departments ask for the probable time of completion time of the repair job and based on the promise of the plant engineer they plan their production. To facilitate this, the plant engineer has to arrange all the jobs according to their due dates of delivery/handing over.

Shortest Process Time (SPT)

This is another policy to adopt for the plant engineering jobs with the concept that the jobs those take less time to repair can be handed over and thus facilitate maximum availability to the machinery.

Longest Process Time (LPT)

In contrast to the above, the job takes longer time will be taken up first and the jobs which take smaller time will be taken up last.

Pre-emptive Priority Rule

When a job is very urgent is will be taken up on priority bases by attending immediately stopping all other jobs. Under this rule the highest priority job is allowed to enter into the service immediately even if another job with lower priority is already in service.

Non-Pre-emptive Priority Rule

In this case highest priority goes ahead in sequence but service is started immediately after completion of the current service.

Priority Service

Priority is given to certain jobs by the virtue of their urgency.

Service In Random Order (SIRO)

Under this rule the jobs are selected for service at random irrespective their arrival, urgency, due date, etc.