number of jobs submitted to the system that each require a maximum of tape drives to complete execution. Assume that each job starts running with three tape drives for a long period before requiring the fourth tape drive for rt period toward the end of its operation. Also assume an endless supply of

Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
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A multiprocessor with eight processors has 20 attached tape drives. There is a
large number of jobs submitted to the system that each require a maximum of
four tape drives to complete execution. Assume that each job starts running with
only three tape drives for a long period before requiring the fourth tape drive for
a short period toward the end of its operation. Also assume an endless supply of
such jobs.
a. Assume the scheduler in the OS will not start a job unless there are four tape dri-
ves available. When a job is started, four drives are assigned immediately and are
not released until the job finishes. What is the maximum number of jobs that can
be in progress at once? What are the maximum and minimum number of tape dri-
ves that may be left idle as a result of this policy?
b. Suggest an alternative policy to improve tape drive utilization and at the same
time avoid system deadlock. What is the maximum number of jobs that can be in
progress at once? What are the bounds on the number of idling tape drives?
Transcribed Image Text:A multiprocessor with eight processors has 20 attached tape drives. There is a large number of jobs submitted to the system that each require a maximum of four tape drives to complete execution. Assume that each job starts running with only three tape drives for a long period before requiring the fourth tape drive for a short period toward the end of its operation. Also assume an endless supply of such jobs. a. Assume the scheduler in the OS will not start a job unless there are four tape dri- ves available. When a job is started, four drives are assigned immediately and are not released until the job finishes. What is the maximum number of jobs that can be in progress at once? What are the maximum and minimum number of tape dri- ves that may be left idle as a result of this policy? b. Suggest an alternative policy to improve tape drive utilization and at the same time avoid system deadlock. What is the maximum number of jobs that can be in progress at once? What are the bounds on the number of idling tape drives?
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