Difference between Sporadic and Aperiodic Real-time Tasks

There are two types of tasks in real-time systems: Periodic tasks, and Dynamic tasks.

Further Dynamic Tasks are classified as:

1. Sporadic Real-time Tasks :
The real-time tasks that reoccur at any random instant and have hard deadline are known as sporadic real-time tasks. Sporadic real-time tasks have some similarity to aperiodic real-time tasks but these tasks are different from aperiodic real-time tasks. Basically all the high critical tasks are sporadic tasks.

For example, fire handling task in industry or emergency message arrival in system are sporadic real-time tasks.

2. Aperiodic Real-time Tasks :
The dynamic tasks that reoccur at any random time and have soft deadline are known as aperiodic real-time tasks. Between two aperiodic real-time tasks the time interval may be even zero. Aperiodic real-time tasks generally include soft real-time tasks.

For example, typing on keyboard or mouse movements are aperiodic real-time tasks.

Difference between Sporadic and Aperiodic Real-time Tasks:

SPORADIC TASK	APERIODIC TASK
It has hard deadline.	It has soft deadline or no deadline.
It is highly critical task.	It is low or moderate critical task.
The minimum separation between two consecutive instances can not be zero.	the minimum separation between two consecutive instances can be zero.
It includes hard real-time tasks.	It includes soft real-time tasks.
Deadline of all instances of sporadic task can be meet easily.	To meet deadline of all instances of aperiodic task is difficult.
It goes through acceptance test.	No testing is performed on aperiodic task.
It is executed only when sufficient slack time is available.	Its execution does not depend on available slack time.
It gets rejected by scheduler when there is less slack time.	It never get rejected by scheduler.
It includes commands given by the system.	It includes interactive commands given by the user.
Example: Security alert program in system.	Example: Logging task in system.