Understanding Operating Systems. 2. How Does Processor Manager Allocate CPU(s) to Jobs?. Process Manager performs job scheduling, process scheduling and interrupt management.In single-user systems, processor is busy only when user is executing a jobat all other times it is idle. Processor manage
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Job Scheduling Versus Process Scheduling
Process Scheduling Policies
Process Scheduling Algorithms
I/O or event completion
I/O or event wait
Handled by Process Scheduler
Handled by Job Scheduler
Maximize throughput by running as many jobs as possible in a given amount of time.
Maximize CPU efficiency by keeping CPU busy 100 % of time.
Ensure fairness for all jobs by giving everyone an equal amount of CPU and I/O time.
Minimize response time by quickly turning around interactive requests.
Minimize turnaround time by moving entire jobs in/out of system quickly.
Minimize waiting time by moving jobs out of READY queue as quickly as possible.
Process CPU Burst (Turnaround Time)
A 15 milliseconds
B 2 milliseconds
C 1 millisecond
What does the time line look like?
What’s the average turnaround time?
first come first served
multiple level queues
non-preemptive scheduling policy
preemptive scheduling policy
Process Control Block
process scheduling algorithm
process scheduling policyprocess status
shortest job next (SJN)
shortest remaining time