# Embedded Systems Questions and Answers – Aperiodic Scheduling

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This set of Embedded Systems Multiple Choice Questions & Answers (MCQs) focuses on “Aperiodic Scheduling”.

1. Which algorithm is based on Jackson’s rule?
a) EDD
b) LL
c) EDF
d) LST

Explanation: The EDD or earliest due date is based on Jackson’s rule. The Jackson’s rule states that for a given a set of n independent tasks, any algorithm that executes the tasks in the order of nondecreasing deadlines is optimal with respect to reducing the maximum lateness. EDF is the earliest deadline first, LL is the least laxity and the LST is the least slack time first.

2. What does EDD stand for?
a) earliest device date
b) earliest due date

Explanation: The earliest due date requires all tasks to be sorted by their deadlines and it is based on Jackson’s rule. If the deadlines are known, EDD algorithm can be used.

3. Which of the following can be implemented as static scheduling algorithm?
a) EDF
b) LL
c) EDD
d) LST

Explanation: The EDD can be implemented as static scheduling algorithm if the deadlines are known in advance and it follows Jackson’s rule.

4. What does EDF stand for?
b) earliest due fix
c) earliest due first

Explanation: The EDF stands for earliest deadline first. This algorithm is optimal with respect to minimizing the maximum lateness and is implemented as dynamic scheduling algorithm for a set of n independent tasks with arbitrary arrival times, any algorithm that at any instant executes the task with the earliest absolute deadline among all the ready tasks is optimal with respect to minimizing the maximum lateness.

5. Which algorithm is dynamic scheduling algorithm?
a) LL
b) LST
c) EDF
d) EDD

Explanation: The EDF or earliest deadline first can be implemented as a dynamic scheduling algorithm.

6. In which scheduling, the task priorities are a monotonically decreasing function of laxity?
a) LL
b) EDD
c) EFD
d) LST

Explanation: In the least laxity algorithm, the laxity can be changed dynamically which shows that the task priorities are a monotonically decreasing function of laxity.

7. Which scheduling algorithm is an optimal scheduling policy for mono-processor system?
a) preemptive algorithm
b) LST
c) EDD
d) LL

Explanation: The least laxity algorithm is a dynamic scheduling algorithm and hence it can be implemented as an optimal scheduling policy for the mono-processor system. The LL scheduling algorithm is also preemptive scheduling.

8. Which scheduling algorithm cannot be used with a standard OS providing fixed priorities?
a) LL
b) LST
c) EDD
d) EFD

Explanation: The least laxity algorithm cannot be used with a standard OS providing fixed priorities because of its dynamic property.

9. Who proposed the LDF algorithm?
a) Bayes
b) Nyquist
c) Lawler
d) Stankovic

Explanation: The latest deadline first or LDF is proposed by Lawler which performs a topological sort. It is based on the total order compatible with the partial order with respect to the task graph.

10. What does LDF stand for?

Explanation: The LDF or latest deadline first is a scheduling algorithm which is proposed by Lawler.

11. Which algorithm is non-preemptive and can be used with a mono processor?
a) LDF
b) pre-emptive
c) aperiodic
d) LL

Explanation: The latest deadline first or LDF is a non-preemptive scheduling algorithm and can be used with a mono processor whereas LL or least laxity is a preemptive scheduling algorithm.

12. Which algorithm requires the periodic checks of the laxity?
a) LST
b) LL
c) EDD
d) EFD

Explanation: The LL scheduling algorithm requires the knowledge of the execution times and the periodic check of the laxity.

13. Who developed the heuristic algorithm?
a) Stankovic and Ramamritham
b) Stankovic and Lawler
c) Lawler
d) Stankovic

Explanation: The heuristic algorithm is developed by Stankovic and Ramamritham in 1991.

14. Which algorithm can be used if the preemptive is not allowed?
a) heuristic algorithm
b) LL
c) EDD
d) LST

Explanation: The heuristic algorithm was proposed by Stankovic and Ramamritham in 1991 can be used if the preemption is not allowed.

15. Deadline interval – execution time =
a) laxity
b) execution time
d) period 