One of the major resources available to the users of an z/OS system is storage. Programs executing in the system, whether user applications or z/OS system routines, are vying for storage. Each of the areas of storage, however, is a limited resource, and use and availability must be managed to maintain program integrity. This managing of storage in z/OS is handled by three storage managers, virtual, real, and auxiliary. In this unit, we will gain an understanding to how each of the areas of storage is assigned, used, and managed is necessary for determining how much storage is required for your installation. This is also required for tuning your system to make the most efficient use of storage, and for analyzing storage-related failures.