Software-Engineering

A software program consists of two modules M₁ and M₂ that can fail independently, but never simultaneously. The program is considered to have failed if any of these modules fails. Both the modules are ‘repairable’ and so the program starts working again as soon as the repair is done. Assume that the mean time to failure (MTTF) of M₁is T₁ with a mean time to repair (MTTR) of R₁. The MTTF of M₂ is T₂ with an MTTR of R₂. What is the availability of the overall program given that the failure and repair times are all exponentially distributed random variables?