In the growing age of advanced technology, the importance of the subject reliability has been felt in almost all manufacturing, engineering and management sectors as a quantitative measure of the adequate functioning of the systems. The existing literature on reliability indicates that the technique of redundancy can be used as one of the effective methods for improving performance of operating systems. In fact, the performance of systems depends on the types of components used, their quantities and the structure in which they are arranged. In the present work, reliability and mean time to system failure (MTSF) of some series-parallel and parallel-series systems have been analyzed by considering arbitrary values of the parameters related to the number of components, operating time and failure rate of the components. The negative exponential distribution is taken up for the failure rate to examine the behaviour of system performance measures graphically and numerically.