Define reliability

Answer 1

Reliability is a measure of the rate of failure in a system that would render it unusable over its expected lifetime. For example, if a component has a reliability of 99.9 percent, it has one chance in a thousand of failing over its lifetime. Although this chance of failure may seem very low, remember that most systems are made up of many components. As you add more components to the system, it becomes more complex and the chance of failure increases. For example, imagine that you are building a complex system made up of seven components, each with 99.9 percent reliability. If none of the components has redundancy built in, the product has a 93.8 percent probability of operating successfully with no component malfunctions over its lifetime. If you build the same type of system using 10 components, each with 99.9 percent reliability, the overall probability of operating without an individual component failure falls to less than 60 percent! Thus, building redundancy into systems that are both complex and safety-critical is imperative.