Earliest Deadline First

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Earliest Deadline First (EDF) is a scheduling method of operating systems, with the help of which it allocates processor time to the processes (English tasks ) . It belongs to the time-based procedures because it makes its decisions in such a way that completion dates (deadlines) are met. The preemptive version of Earliest Deadline First is mainly used for real-time systems.


  • All tasks that are available at the point in time under consideration are arranged according to ascending completion dates (deadlines)
  • The task that has to be finished first receives the processor

There are always times for scheduling considered, where a new task is started either or barely active task is completed.

EDF is very flexible because it can be used for both preemptive and cooperative multitasking . It can also be used in aperiodic and periodic plans.

Processor usage

EDF can schedule the processor up to the maximum processor utilization. However, this only applies to task systems in which the time span until the deadline of a task is greater than or equal to the period of the respective task itself. Furthermore, there must be no dependencies between the tasks and no shared resource may be used, as this could cause a deadlock .

See also