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SHORTEST PROCESSING TIME (SPT) RULE

SHORTEST PROCESSING TIME (SPT) RULE

This-rule says that jobs are sequenced in such a way that the job with least processing time is picked up-first, followed by the job with the next smallest processing time (SPT) and so on. This is referred to as shortest processing time sequencing. However, when the importance of the jobs to be performed varies, a different rule called Weight-Scheduling (WSPT) rule is used weights are allotted to jobs, greater weight meaning more important job. Let Wi be the weight allotted. By dividing the processing time by the weight factor, the tendency to move important job to an earlier position in the order is achieved.

12t[1]W[1]≤t[2]W[2]≤…t[n]W[n]“>

The numbers in brackets above define the position of the jobs in the optimal sequence.

Example 7.1. Consider the 8 jobs with processing times, due dates and importance weights as shown below.

8 jobs one machine case data

12=3.53 jobs.