A firm that specializes in desktop publishing for local charities has agreed to take on the following jobs. The firm has not decided which dispatching rule to apply in order to prioritize the jobs and fix them into the schedule
All dates are specified as days from today.
Time Due Date
Job 1 20 25
Job 2 15 20
Job 3 7 16
Job 4 25 50
Job 5 31 33
Job 6 43 55
a. Complete the following table. Show your supporting calculations below.
b. Which dispatching rule has the best score for flow time?
c. Which dispatching rule has the best score for work-in-process (jobs in the system)?
d. Which dispatching rule has the best score for lateness?
Dispatching Rule
Job Sequence Average
Flow Time Average Number of Jobs
Average Lateness
FCFS
EDD
SPT
LPT
(a) The table of results appears below. A supporting table for each dispatch rule also follows.
Dispatching Rule
Job sequence Average
Flow Time Average Number of Jobs Average Lateness
FCFS 1-2-3-4-5-6 67.2 2.86 34.8
EDD 3-2-1-5-4-6 63.8 2.71 32.2
SPT 3-2-1-4-5-6 62.8 2.67 31.2
LPT 6-5-4-1-2-3 101.7 4.33 70.5
(b, c, d) The SPT rule is best for flow time, for average jobs in system, and for average lateness.
FCFS Time Due Date Slack Flow time Late days
Job 1 20 25 5 20 0
Job 2 15 20 5 35 15
Job 3 7 16 9 42 26
Job 4 25 50 25 67 17
Job 5 31 33 2 98 65
Job 6 43 55 12 141 86
Total 403 209
Average 67.17 34.83
Average number of jobs in system: 2.858
EDD Time Due Date Slack Flow time Late days
Job 3 7 16 9 7 0
Job 2 15 20 5 22 2
Job 1 20 25 5 42 17
Job 5 31 33 2 73 40
Job 4 25 50 25 98 48
Job 6 43 55 12 141 86
Total 383 193
Average 63.83 32.17
Average number of jobs in system: 2.716
SPT Time Due Date Slack Flow time Late days
Job 3 7 16 9 7 0
Job 2 15 20 5 22 2
Job 1 20 25 5 42 17
Job 4 25 50 25 67 17
Job 5 31 33 2 98 65
Job 6 43 55 12 141 86
Total 377 187
Average 62.83 31.17
Average number of jobs in system: 2.674
LPT Time Due Date Slack Flow time Late days
Job 6 43 55 12 43 0
Job 5 31 33 2 74 41
Job 4 25 50 25 99 49
Job 1 20 25 5 119 94
Job 2 15 20 5 134 114
Job 3 7 16 9 141 125
Total 610 423
Average 101.67 70.5
Average number of jobs in system: 4.326
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