Difference between Hard and Soft Real Time System | Real Time System

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hard and soft real time systemDifference between Soft and Hard Real Time System,
Real Time System Notes | Sixth Semester,
BSc.CSIT | Tribhuvan University (TU)

Hard and soft real time system
A hard real time system guarantees that critical tasks complete on time, whereas in soft real time system, a critical real time task gets priority over other tasks and retains that priority until it completes. For more detail difference between hard and soft real time system, see the following difference table;

S.N Hard Real Time System Soft Real Time System
1 Timing constraint is hard if the failure to meet it is considered a fatal error. A timing constraint is soft if a few misses of deadlines do no serious harm, only the system’s overall performance becomes poorer and poorer when more and more jobs with soft deadlines complete late.
2 The usefulness of a result produced by hard real time job falls off abruptly and even become negative when the tardiness of the job becomes larger than zero. The usefulness of a result produced by soft real time job decreases gradually as the tardiness of the job increases.
3 User can obtain the validation as systems is to avoid hardware and software features that lead to non-determinism. Therefore, it is possible to verify the satisfaction of all hard timing constraint by exhaustive simulation and testing. Less rigorous validation as more relaxed time constraint allow the developer to consider other performance metric equally seriously.
4 Completion of task or job is deterministic. Completion of task or job is probabilistic.
5 Hard-required response time. Soft-required response time.
6 Predictable peak load performance. Degraded peak load performance.
7 Controlled by environment. Controlled by computer.
8 Autonomous error detection. User assisted error detection.
9 Short-term data integrity Long-term data integrity
10 Small/medium size of data files Large size of data files
11 Example: Flight control, railway signaling, robot, anti missile system, inkjet printer etc. Example: Dvd player, mobile phone, on-line transaction systems, telephone switches, electronic games, multimedia system, web browsing etc.
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