What are the different tasks in the real time system?

In embedded system, real time means the following −

  • The system responds to an event or request within timing constraints.

  • System must use a real time operating system, that system can interrupt a running task.

  • The system must be predictable. The system guarantees that important tasks get run in fixed time constraints.

Real time systems work in time constraints and provide estimated time for critical situations.

Embedded systems provide specific functions in a large operating system.


Generally, the tasks in the system are said to be fully pre-emptive and that are used to communicate with the rest of the system via data read at the beginning and written at the end of their executions.

The different tasks in real time system are as follows −

Periodic task of a real time system

In general periodic tasks execute their invocations within the preferred regular time intervals.

Example − Let us consider a task T(P) that is characterized by its worst case execution time represented as (w cet), and the period (p) with relative deadline (dl). Now that the k th invocation of T(P) is characterized by its earliest start time (est) and relative deadline (dl).

Periodic tasks with the complex constraints that have been transformed to offline are referred to as an offline task.

Aperiodic task of a real time system

The aperiodic tasks are invoked only once. Their respective arrival times are unknown at the design time.

Example − T(A) has the arrival time (ar), worst case execution time and relative deadline as the parameters. But when coming to the soft aperiodic tasks, they have no deadline constraints.

Sporadic task of a real time system

These tasks can arrive at the system at arbitrary points or even at different points in time, but with defined minimum inter-arrival times between two consecutive invocations.

Example − Let us consider a sporadic task T(S) is characterized by its relative deadline, minimum inter-arrival time and worst case execution time. In this case these attributes are known before the run-time of the system. At the same time the additional information available is its arrival time and its absolute deadline.