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MSCI432 Lecture Notes - Mainframe Computer, Job Shop, Customer Service

Management Sciences
Course Code
Binyamin Mantin

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1. Discuss each of the following objectives listed and the relationship each has with job shop performance
a. Reduce WIP inventory
b. Provide a high level of customer service
c. Reduce worker idle time
d. Improve factory efficiency
a) WIP inventory is Work-In-Progress inventory. This refers to inventory waiting to be
processed and inventory currently being processed. Since there are opportunity costs
associated with holding inventory (discussed in detail in Chapter 4), the firm would like to
reduce the WIP inventory as much as possible. However, too low levels of WIP inventory
could make coordination of separate processes difficult.
b) Customer service can be measured by fill rate, namely the proportion of demands satisfied
(discussed in detail in Chapter 5). The likelihood of meeting scheduled deliveries increases
if jobs can flow quickly and smoothly through the system. This measure of performance
could suffer if WIP inventories are reduced too severely.
c) Idle time results when the smooth flow of goods is interrupted and workers must wait.
Obviously, idle time is undesirable and can be very costly to the firm.
d) One measure of factory efficiency is the relationship between the cost of running the factory
and the revenue generated by the goods it produces. Factory efficiency can be improved by
increasing the plant's throughput rate.
5. Five jobs must be scheduled for batch processing on a mainframe computer system (this
question must be updated… Anyway, I decided to keep the wording of the textbook). The
processing times and the promised time for each of the jobs are listed here.
Job 1 2 3 4 5
Processing time 40 min 2.5hr 20min 4hr 1.5hr
Promised time 11:00am 2:00pm 2:00pm 1:00pm 4:00pm
Assume that the current time is 10:00am.
a. If the jobs are scheduled according to SPT, find the tardiness of each job and the mean
tardiness of all jobs.
b. Repeat the calculation in part (a) for EDD scheduling.
Scheduling by SPT means that the jobs are processed in the sequence 3-1-5-2-4.
SPT Sequencing
Job Time Completion Time Promised Time Tardiness(hrs)
3 20 min. 10:20 a.m. 2:00 p.m. 0
1 40 min. 11:00 a.m. 11:00 a.m 0
5 1.5 hrs. 12:30 p.m. 4:00 p.m. 0
2 2.5 hrs. 3:00 p.m. 2:00 p.m. 1
4 4 hrs. 7:00 p.m. 1:00 p.m 6
Mean tardiness = 7/5 hrs. = 1.4 hours.
The EDD sequence is 1-4-2-3-5 (or 1-4-3-2-5).
EDD Sequencing
Job Time Completion Time Promised Time Tardiness(hrs)
1 40 min. 10:40 a.m. 11:00 p.m. 0
4 4 hrs. 2:40 p.m. 1:00 p.m. 1-2/3
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