Conventional object-oriented programming systems allow application programmers to structure each application as a set of objects. They do not allow long-term storage of the objects, nor do they allow sharing and concurrency within the object spaces. Persistent object systems and object-oriented databases have been developed to address some of these shortcomings. Persistent object systems provide the ability to store, share and dynamically reuse the object instances and object structures that the application creates or uses. A persistent object system depends upon a store (on secondary memory) to provide the persistence. In addition the store is responsible for the provision of services such as object identity or naming, type security, retrieval, sharing support, locking and concurrency control, consistency control and other features necessary for the management of long-lived objects. Persistent stores have used many techniques to provide the above. The two most common are the object-oriented database and the specialized object-container based stores. We are investigating the use of memory mapping combined with a storage manager to provide a distributed object store. This paper presents the design and implementation of SPOMS which is a memory-mapped store built on top of the Mach operating system.