The SHMEM privilege lets the user's process create global sections and mailboxes (permanent and temporary) in memory shared by multiple processors if the process also has appropriate PRMGBL, PRMMBX, SYSGBL, and TMPMBX privileges. Just as in local memory, the space required for a temporary mailbox in multiport memory counts against the buffered I/O byte count limit (BYTLM) of the process.

The privilege also lets a user's process create or delete an event flag cluster in shared memory using the Associate Common Event Flag Cluster ($ASCEFC) or the Disassociate Common Event Flag Cluster ($DACEFC) system service.