Abstract: A storage hierarchy has a backing store and a caching buffer store. During a series of accesses to the hierarchy by a user, writing data to the hierarchy results in data being selectively removed from the buffer store. Space in said buffer store not being allocated to data being written results in such data being written to the backing store to the exclusion of the buffer store. Removal of data increases the probability of writing data to the backing store. In a preferred implementation, the backing store is one or more disk type data storage apparatus and the buffer store is an electronic random access memory.