Slides - Åbo Akademi

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More Definitions Failure rate (or failure intensity): the number of failures per time unit (hour, second, ...) or per natural unit (transaction, run, ...) • can be considered as an alternative way of expressing reliability Availability: the ability of a system to be in a state to deliver correct service under given conditions at a specified instant of time • usually measured by the average (over time) probability that a system is operational in a specified environment Maintainability: the ability of a system to be restored to a state in which it can deliver correct service • usually measured by the probability that maintenance of the system will restore it within a given time period
Safety-critical Systems • Pervasive use of computer-based systems in many critical infrastructures • flight/traffic control, driverless trains/cars operation, nuclear plant monitoring, robotic surgery, military applications, etc. • Extremely high reliability requirements for safety-critical systems • avionics domain example: failure rate ≤ 10 −9 failures per hour, i.e., more than a hundred years of operation without encountering a failure
Page 1 and 2: Software Safety Lecture 8: System R
Page 3: Reliability Definition Reliability:
Page 7 and 8: Hardware Failures The system is sai
Page 9 and 10: Failure Rate (ctd.) Classification
Page 11 and 12: Most Important Distributions Discre
Page 13 and 14: Reliability Parameters MTTF: Mean T
Page 15 and 16: Exponential Distribution The distri
Page 17 and 18: MTTF Example A system with a consta
Page 19 and 20: Example: Failure Rate Calculation F
Page 21 and 22: Series Systems Such a configuration
Page 23 and 24: Series-Parallel Combinations The mo
Page 25 and 26: M-of-N Arrangement A system consist
Page 27 and 28: Failure rate The term failure inten
Page 29 and 30: Design diversity Each variant of so

Slides - Åbo Akademi

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