Safety-critical systems

Overview

Safety-critical system, triple modular redundant system and diverse programming.

What you need to know

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Questions from this subtopic

Each one with the model answer underneath.

1. 1

   Define a safety-critical system.

   Model answer

   A safety-critical system is one whose failure could cause death, serious injury or severe environmental damage.

2. 2

   Give three examples of safety-critical systems.

   Model answer

   Aircraft flight control, railway signalling and nuclear plant control are all safety-critical. Hospital equipment such as an infusion pump is too.

3. 3

   Define dependability.

   Model answer

   Dependability is the degree to which a system can be relied upon to behave correctly when it is needed. Reliability, availability and safety all contribute.

4. 4

   Why does a safety-critical system need a higher level of dependability than an office application?

   Model answer

   A crashed office application costs an hour of work. A failed flight control system costs lives.

5. 5

   State two development practices used on safety-critical systems that are unusual elsewhere.

   Model answer

   Formal mathematical proof of correctness is used on critical sections. Independent teams review and test everything the developers produce.

6. 6

   What is redundancy in a safety-critical system?

   Model answer

   Redundancy is the provision of duplicate components so that a failure does not stop the system. A second processor takes over from a failed one.

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