One embodiment of the invention is directed to providing a single instance storage capability in a content addressable computer system that stores content units in a time-based directory structure. Another embodiment is directed to managing access to content units that do not include a timestamp in their content addresses, in a time-based directory structure. A further embodiment is directed to accessing replicated content units stored on a computer, based on a time of replication. A further embodiment is directed to employing a bitmap in a time-based directory structure which may be used to indicate whether any content units stored during a specified time range are stored in the directory structure.