This paper presents the effect of number of servers on the reliability function of a 2-unit cold standby system subject to repair and preventive maintenance. The stochastic behaviour, concerning reliability analysis, of two models is discussed. In Model I a single sever facility is available for performing repair and preventive maintenance. In Model II two server (non- exchangeable and exchangeable) facilities are available. Explicit expressions for the Laplace transform of the first passage time distribution, and the mean time to system failure are derived, by applying the regeneration point technique, under the assumption that all the distributions are arbitrary. A basic result is obtained showing that the system reliability, R(t), remains unchanged whether a single server is used or two servers are used.