BRAINSCAPE1
CSCI 3120 Final Exam with
complete solutions latest version
Round robin scheduling algorithm - CORRECT ANSWER-Processes given a time
quantum, runs for this amount of time before it is preempted. Ready queue is still FCFS
Average wait time vs. response time for RR - CORRECT ANSWER-Long average wait
time, short response time
Performance of RR relative to time quantum length - CORRECT ANSWER-Large time
quantum makes it like FCFS, small time quantum has lots of overhead because of many
context switches
Turnaround time of RR relative to time quantum length - CORRECT ANSWER-
Improves when time quantum is the same length as a process' burst time, worsens
otherwise
Priority scheduling - CORRECT ANSWER-Each process given priority, process
scheduled based on priority, equal priorities is scheduled with FCFS, low number
represents high priority
Internal priorities - CORRECT ANSWER-Using some measurable quantity to compute
the priority of a process (ex: memory requirements, number of open files)
External priorities - CORRECT ANSWER-Set by criteria outside the OS (ex: importance
of process, type/amount of funds for computer)
Major problem with priority scheduling - CORRECT ANSWER-Indefinite
blocking/starvation (process ready but never gets the CPU)
Solution to indefinite blockage of low priority processes - CORRECT ANSWER-Aging
(gradually increasing priority of processes that wait in the system for a long time
BRAINSCAPE1
, BRAINSCAPE1
Priority scheduling with RR - CORRECT ANSWER-Both scheduling algorithms
combined so that system executes highest priority process using priority scheduling,
and processes with the same priority with RR
Priority scheduling in regards to preemptiveness - CORRECT ANSWER-Can be either
preemptive (gives CPU to incoming process with higher priority), or nonpreemptive
(incoming processes are put into the ready queue)
Search complexity for typical priority scheduling with one queue - CORRECT ANSWER-
O(n)
Multilevel queue scheduling - CORRECT ANSWER-Separate queues for each priority,
scheduler schedules the processes in the highest priority queue. Each queue can run a
difference scheduling algorithm
Methods of scheduling between queues in multi queue scheduling - CORRECT
ANSWER-Fixed priority preemptive scheduling, time slice among queues
Fixed priority preemptive scheduling - CORRECT ANSWER-Scheduling among queues
in multilevel queue scheduling (ex queue 1 may have absolute priority over queue 2)
Time slice among queues - CORRECT ANSWER-Each priority queue gets CPU for
certain amount of time to schedule its processes
Advantages/disadvantages of normal multilevel queue scheduling - CORRECT
ANSWER-Advantage: low scheduling overhead, disadvantage: inflexible setup
Multilevel feedback queue scheduling - CORRECT ANSWER-Processes can move
between queues, based on process' CPU burst characteristics (ex process on CPU too
long moves to lower priority queue, or process waiting moves to higher priority queue)
What problem does multilevel feedback queue scheduling combat - CORRECT
ANSWER-Process starvation
Characteristics that define a multilevel feedback queue - CORRECT ANSWER-Number
of queues, scheduling algorithm for each queue, scheduling algorithm between queues,
method to determine when a process is moved to a higher/lower queue, method to
determine which queue an incoming process will enter
What is the most general CPU scheduling algorithm - CORRECT ANSWER-Multilevel
feedback queue scheduling (also most complex)
What is scheduled on most OS's - CORRECT ANSWER-Kernel level threads
On many-to-one/many-to-many systems, what steps are required to allocate CPU to
user level thread - CORRECT ANSWER-Process contention scope (PCS): threads
belonging to same process are scheduled locally to be mapped to kernel level thread,
BRAINSCAPE1
CSCI 3120 Final Exam with
complete solutions latest version
Round robin scheduling algorithm - CORRECT ANSWER-Processes given a time
quantum, runs for this amount of time before it is preempted. Ready queue is still FCFS
Average wait time vs. response time for RR - CORRECT ANSWER-Long average wait
time, short response time
Performance of RR relative to time quantum length - CORRECT ANSWER-Large time
quantum makes it like FCFS, small time quantum has lots of overhead because of many
context switches
Turnaround time of RR relative to time quantum length - CORRECT ANSWER-
Improves when time quantum is the same length as a process' burst time, worsens
otherwise
Priority scheduling - CORRECT ANSWER-Each process given priority, process
scheduled based on priority, equal priorities is scheduled with FCFS, low number
represents high priority
Internal priorities - CORRECT ANSWER-Using some measurable quantity to compute
the priority of a process (ex: memory requirements, number of open files)
External priorities - CORRECT ANSWER-Set by criteria outside the OS (ex: importance
of process, type/amount of funds for computer)
Major problem with priority scheduling - CORRECT ANSWER-Indefinite
blocking/starvation (process ready but never gets the CPU)
Solution to indefinite blockage of low priority processes - CORRECT ANSWER-Aging
(gradually increasing priority of processes that wait in the system for a long time
BRAINSCAPE1
, BRAINSCAPE1
Priority scheduling with RR - CORRECT ANSWER-Both scheduling algorithms
combined so that system executes highest priority process using priority scheduling,
and processes with the same priority with RR
Priority scheduling in regards to preemptiveness - CORRECT ANSWER-Can be either
preemptive (gives CPU to incoming process with higher priority), or nonpreemptive
(incoming processes are put into the ready queue)
Search complexity for typical priority scheduling with one queue - CORRECT ANSWER-
O(n)
Multilevel queue scheduling - CORRECT ANSWER-Separate queues for each priority,
scheduler schedules the processes in the highest priority queue. Each queue can run a
difference scheduling algorithm
Methods of scheduling between queues in multi queue scheduling - CORRECT
ANSWER-Fixed priority preemptive scheduling, time slice among queues
Fixed priority preemptive scheduling - CORRECT ANSWER-Scheduling among queues
in multilevel queue scheduling (ex queue 1 may have absolute priority over queue 2)
Time slice among queues - CORRECT ANSWER-Each priority queue gets CPU for
certain amount of time to schedule its processes
Advantages/disadvantages of normal multilevel queue scheduling - CORRECT
ANSWER-Advantage: low scheduling overhead, disadvantage: inflexible setup
Multilevel feedback queue scheduling - CORRECT ANSWER-Processes can move
between queues, based on process' CPU burst characteristics (ex process on CPU too
long moves to lower priority queue, or process waiting moves to higher priority queue)
What problem does multilevel feedback queue scheduling combat - CORRECT
ANSWER-Process starvation
Characteristics that define a multilevel feedback queue - CORRECT ANSWER-Number
of queues, scheduling algorithm for each queue, scheduling algorithm between queues,
method to determine when a process is moved to a higher/lower queue, method to
determine which queue an incoming process will enter
What is the most general CPU scheduling algorithm - CORRECT ANSWER-Multilevel
feedback queue scheduling (also most complex)
What is scheduled on most OS's - CORRECT ANSWER-Kernel level threads
On many-to-one/many-to-many systems, what steps are required to allocate CPU to
user level thread - CORRECT ANSWER-Process contention scope (PCS): threads
belonging to same process are scheduled locally to be mapped to kernel level thread,
BRAINSCAPE1
