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.|
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