In this paper we study the performance characteristics of a replicated data base under two different updating policies. In the synchronous case requests for any replications of the data base can be processed only if no copies of data base are being updated due to a previous write request, whereas in the non-synchronous case read requests are allowed to be processed at any time if there is a free data base copy. We formulate a queueing theoretic model of the system assuming a Poisson arrival process for both read and write requests. This model is then solved using the matrix geometric solution method and the relevant performance metrics are derived and analyzed. © 1985.