What are three influences on the reliability of a system?

What are three influences on the reliability of a system?
Ans: In a socio-technical system, you need to consider reliability from three perspectives:
1. Hardware reliability: What is the probability of hardware components failing and how long does it take to repair a failed component?
2. Software reliability: How likely is it that a software component will produce an incorrect output? Software failure is distinct from hardware failure in that software does not wear out. Failures are often transient. The system carries on working after an incorrect result has been produced.
3. Operator reliability: How likely is it that the operator of a system will make an error and provide an incorrect input? How likely is it that the software will fail to detect this error and propagate the mistake?