Scheduling

Question 1

Round Robin

Answer 1

A pre-emptive scheduling algorithm designed for time sharing systems.
The ready (to run) queue is treated as a circular queue.
A small execution time interval is defined as the time slice.

Question 2

Shortest Job First

Answer 2

A type of scheduling algorithm where the queue is sorted by expected execution time. New jobs are added accordingly to the queue.

Question 3

First Come, First Served (FCFS)

Answer 3

The first job to enter the ready queue is the first to enter the running state.

Question 4

Shortest Remaining Time

Answer 4

A type of scheduling algorithm where the queue is sorted by expected execution time. New and pre-empted jobs are added accordingly to the queue.

Question 5

Multi-Level Feedback Queue (MLFQ)

Answer 5

A scheduling algorithm that deals with tasks based on a set of priorities and rules across different queues. Processes may get promoted, demoted or stay at the same level.

Question 6

Preemptive scheduling algorithms

Answer 6

Round Robin, Shortest Remaining Time and MLFQ

Question 7

Non preemptive scheduling algorithms

Answer 7

First Come First Served, Shortest Job First

Question 8

Advantages of First Come First Served

Answer 8

*Simple to implement with a queue data structure.

*Works well with processes which need shorter amounts of CPU time

Question 9

Disadvantages of First Come First Served

Answer 9

*Longer processes may monopolise the CPU.
*User may experience a lack of responsiveness.
*Does not maximize throughput if there are longer processes.

Question 10

Advantages of Round Robin

Answer 10

*Improves the throughput of processes and prevents longer processes from monopolising the CPU.

Question 11

Disadvantages of Round Robin

Answer 11

*Swapping processes has an admin cost which can slow down if the time slice used is too small.

*User may experience a lack of responsiveness if there are a large number of processes.

Question 12

Advantages of Shortest Job First

Answer 12

*Prioritises processes using slower computer resources.

*Prioritises GUI operations.

Question 13

Disadvantages of Shortest Job First

Answer 13

*May suffer from starvation for longer processes.
*Not as fair as other scheduling algorithms.

Question 14

Advantages of Shortest Remaining Time

Answer 14

*Improves the throughput of processes.
*Longer processes will increase in priority over time.

Question 15

Disadvantages of Shortest Remaining Time

Answer 15

*May suffer from starvation for longer processes, but is mitigated.
*Not as fair as other scheduling algorithms.

Question 16

Advantages of MLFQ

Answer 16

*Prioritises processes using slower computer resources by promoting these processes.
*Prioritises GUI operations as they will always enter at level 0.

Question 17

Disadvantages of MLFQ

Answer 17

*Longer, poorly coded, processes may suffer from starvation.