Dynamic Storage Pools

In addition to paged virtual memory, OpenVMS maintains two memory pools—the nonpaged dynamic storage pool and the paged dynamic storage pool. They are generally referred to as the "nonpaged pool" and "paged pool" and are located in the system virtual address range.

The nonpaged pool, as its name implies, is not paged. None if its contents are removed from physical memory. It is used to store data that must be resident in memory at all times, such as data structures describing open files and I/O operations in progress. The paged pool contains certain systemwide data that may be paged out, including a list of mounted disk volumes, for example.

Within the pools, OpenVMS maintains lists of packets available for allocation by a process or for use by OpenVMS itself. The packets are of varying sizes designed to satisfy a wide variety of requirements while balancing wasted space against processing overhead.

Processes usually allocate pool space indirectly as a result of OpenVMS routines. Special privileges are required to manipulate pool contents directly.