HP OpenVMS Guide to System Security: OpenVMS Version 8.4 > Appendix A Assigning Privileges
The PFNMAP privilege lets a user's process create and map page frame number (PFN) global sections to specific pages of physical memory or I/O device registers, no matter who is using the pages or registers. Such a privileged process can also delete PFN-based global sections with the system service $DGBLSC.
Exercise caution when granting this privilege. If unqualified user processes have unrestricted access to physical memory, the operating system and service to other processes can be easily disrupted. Such disruptions can include failure of the system, destruction of all system and user data, and exposure of confidential information.