The 'bathtub' curve is a model for system reliability including early life burn-in and eventual wear-out at the system's end of life. For software systems, the reliability remains nearly constant with no wear-out other than associated hardware.

Almost all reliability diagrams use some sort of exponential distribution to depict the early-life stages of a system. But is that always the case?

Hardware Failure ('Bathtub') Curve Early-Life Curves Early Life Early Life Wear Out Failure Rate Failure Rate Time Time