IT 342 EXAM 2 STUDY GUIDE
Aims of Schedulers - Answers - Fairness - equal opportunity to execute
Predictability - same job should run in about same time, at same cost, regardless of
system load
Resource use - good mix of CPU and I/O intensive operations
Optimize system resources
Maintain metrices
Metrics of scheduler - Answers - CPU Utilization
Turnaround Time
Waiting time of a process
Response time
Time consumed by the dispatcher - Answers - Dispatcher Latency
Length of a CPU burst - Answers - the length of time a process would continue
executing if given the processor are not preempted
Preemption - Answers - When a process is switched by the dispatcher from the CPU
before it completes
Scheduling Algorithms - Answers - First Come First Served
Shortest Job First
Shortest Job Remaining First
Priority
Round Robin
Multilevel Queue
Multilevel Feedback
First Come First Served - Answers - Processes enter the back of the queue and are
taken from the top
Not preemptive
Easy to implement
Waiting Time is high on average
Great for all long, CPU bound processes
Short jobs penalized, I/O bound processes penalized
Shortest-Job First - Answers - Selects the process that has the smallest CPU burst time
Can be thought of as selecting the process with
Not preemptive
Easy to implement
Must know CPU burst Time
, Shortest-Job-Remaining First - Answers - Selects the process that has the smallest
CPU burst time
Preemptive - If a new process arrives with a CPU burst length less than remaining time
of the current executing process, preempt
Easy to implement
Priority - Answers - Selects the process with the highest priority
-Size of the process
-Nature of the process
-Type of the process
Resource requirements of the process:
Easy to implement
Must set priority
Starvation possible - Starvation occurs when a low priority process does not get the
chance to execute because high priority processes keep arriving lead to starvation
Starvation - Answers - Processes are in the starved state when they are available but
never get a chance to execute
Priority Considerations - Answers - Size of Process
Nature of Process
Type of Process
Resource requirements of Process
User input
Round Robin - Answers - Processes enter the back of the queue and are taken from the
top
Using time slice
Easy to implement
Context switching overhead is high
Most commonly used scheduling method
Time Slice, Quanta - Answers - assigned to each process in equal portions and in
circular
Multilevel Queue - Answers - Maintains separate queues for each group of processes
that remain in that queue.
System processes, Interactive Processes
Each queue can have a different scheduling algorithm
Most of the time it is used for priority
Even if not the case, the queues have priority
Very Complex
Can lead to starvation
Multilevel Feedback Queue - Answers - Maintains several queues
Aims of Schedulers - Answers - Fairness - equal opportunity to execute
Predictability - same job should run in about same time, at same cost, regardless of
system load
Resource use - good mix of CPU and I/O intensive operations
Optimize system resources
Maintain metrices
Metrics of scheduler - Answers - CPU Utilization
Turnaround Time
Waiting time of a process
Response time
Time consumed by the dispatcher - Answers - Dispatcher Latency
Length of a CPU burst - Answers - the length of time a process would continue
executing if given the processor are not preempted
Preemption - Answers - When a process is switched by the dispatcher from the CPU
before it completes
Scheduling Algorithms - Answers - First Come First Served
Shortest Job First
Shortest Job Remaining First
Priority
Round Robin
Multilevel Queue
Multilevel Feedback
First Come First Served - Answers - Processes enter the back of the queue and are
taken from the top
Not preemptive
Easy to implement
Waiting Time is high on average
Great for all long, CPU bound processes
Short jobs penalized, I/O bound processes penalized
Shortest-Job First - Answers - Selects the process that has the smallest CPU burst time
Can be thought of as selecting the process with
Not preemptive
Easy to implement
Must know CPU burst Time
, Shortest-Job-Remaining First - Answers - Selects the process that has the smallest
CPU burst time
Preemptive - If a new process arrives with a CPU burst length less than remaining time
of the current executing process, preempt
Easy to implement
Priority - Answers - Selects the process with the highest priority
-Size of the process
-Nature of the process
-Type of the process
Resource requirements of the process:
Easy to implement
Must set priority
Starvation possible - Starvation occurs when a low priority process does not get the
chance to execute because high priority processes keep arriving lead to starvation
Starvation - Answers - Processes are in the starved state when they are available but
never get a chance to execute
Priority Considerations - Answers - Size of Process
Nature of Process
Type of Process
Resource requirements of Process
User input
Round Robin - Answers - Processes enter the back of the queue and are taken from the
top
Using time slice
Easy to implement
Context switching overhead is high
Most commonly used scheduling method
Time Slice, Quanta - Answers - assigned to each process in equal portions and in
circular
Multilevel Queue - Answers - Maintains separate queues for each group of processes
that remain in that queue.
System processes, Interactive Processes
Each queue can have a different scheduling algorithm
Most of the time it is used for priority
Even if not the case, the queues have priority
Very Complex
Can lead to starvation
Multilevel Feedback Queue - Answers - Maintains several queues
