Single address space systems (SASOS) provide a programming model that is well suited to supporting persistent object systems. In this paper we show that stability can be implemented in the Mungi SASOS without incurring overhead in excess of the inherent cost of shadow-paging. Our approach is based on the introduction of a limited form of aliasing into the SASOS model and makes heavy use of user-level page fault handlers to allow implementation outside the kernel. We also show how the demands of database systems for control over page residency and physical I/O can be accommodated. An approach to user-level implementation of distributed shared memory (DSM) coherency models is outlined.