Parallel systems are magnificently used in engineering due to availing a longer and more reliable lifetime of systems. Recently, employing standby units in systems has increased the reliability and finally benefits of the system. In application situations, the components of a system are related to them. So in these cases, the independence assumption is not hold true and we must evaluate the reliability of system under some kinds of dependence concepts. In this paper, the two-unit parallel system with -$ n-2 $- cold standbys components is assumed where the units lifetimes are dependent. Some important formulas for computing the mean time to system failure are given according to the effects of dependence parameter on reliability of the system. Then, the mean time to failure of -$ 2,n-2 $- system is estimated based on some dependence estimators. Finally, a simulation study are used to examine and evaluate the system lifetime and also compare the efficiencies of mean time to system failure estimators.

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