# Difference between Fixed priority and Dynamic priority Algorithm | Real Time System

## Difference between Fixed priority and Dynamic priority Algorithm, Real Time System Notes | Sixth Semester, BSc.CSIT | Tribhuvan University (TU)

Fixed Priority Versus Dynamic Priority Algorithms
Priority-driven algorithms differ from each other in how priorities are assigned to jobs. We classify algorithms for scheduling periodic tasks into two types: fixed priority and dynamic priority algorithm. These algorithms are described as difference in tabular form as follows;

 Fixed Priority Algorithm Dynamic Priority Algorithm A fixed priority algorithm assigns the same priority to all jobs in each task A dynamic priority algorithm assigns different priorities to the individual jobs in each task. Priority of each periodic task is fixed relative to other tasks. Priority of task with respect to that of other task change as the jobs are released and completed. Fixed priority algorithms are used much in practical real time purposes than dynamic priority algorithm. Dynamic priority algorithms are used less in practical real time purposes than fixed priority algorithm. This algorithm doesn’t perform well in terms of schedulable utilization. Outperforms fixed priority in terms of schedulable utilization. Timing behavior is more predictable in fixed priority algorithm. Timing behavior is less predictable in dynamic priority algorithm. Generally fixed priority algorithms are not optimal. Generally dynamic priority algorithms are optimal. These algorithms leads to stable system. These algorithms may lead to unstable system. Example: Rate monotonic algorithm, Deadline monotonic algorithm. Example: EDF, LST, FIFO, LIFO
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