Topic D Flashcards
What is the job of the scheduler?
The scheduler selects next job from ready queue
What does non-preemptive mean?
once a process has been allocated to the CPU it stays on there until it terminates
What can be considered when picking a scheduling policy?
- maximise throughput
- minimise response time
- minimise turn around time
- minimise waiting time
- maximise CPU efficiency
- Ensure fairness
How do you calculate a FCFS average wait time?
add individual wait times together then divide by the number of processes
How do you calculate a shortest job first average wait time?
reorder processes depending on their burst time, add individual wait times together then divide by the number of processes
Disadvantage of non-preemptive
Leads to process starvation
what is the shortest remaining time first ?
The preemptive version of shortest job first (not going to be asked for average wait time)
what can character can be set to by the user or assigned to by the OS to do with higher process priority?
- memory usage
- I/O throughput
- Total CPU time
- Time already elapsed
How do you calculate a Priority Scheduling average wait time?
reorder processes depending on the highest priorities, add individual wait times together then divide by the number of processes
what is aging?
a method used to combat process starvation by increasing the priority of processes that having been waiting a long time in the queue.
How do you calculate a Round Robin average wait time?
add the time slice if the burst time is longer, or add the burst time if it’s shorter than time slice then divide by the number of processes
What is turn around time?
turn around time is the time when it terminated minus the time when it arrived in the process queue
What is wait time?
it’s turn around time minus it’s burst time
How do you calculate a Round Robin average turn around time?
you don’t minus the amount of time while it’s not processing, add them all together and divide by the number of processes
