Redundancy is a technique that has been widely applied to improve the system reliability and its availability. In this paper, a new switching model is proposed to increase the reliability of a unit (system) with a cold standby backup. It is assumed that the switch over to the standby unit is not failure-free, contrary to what we have in standby redundancy. The optimal time to switch between the key unit and its cold standby backup is find such that the mean lifetime of the system to be maximized. Finally, an example is presented to compare the mean lifetime of the proposed switch- ing model and a system with parallel redundancy.

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