PIOPAGES specifies the size of the process I/O segment, which
    holds data structures and buffer pool space for RMS to use
    when it handles I/O that involves process-permanent files. Once
    PIOPAGES is reset in SYSGEN, any new process receives the changed
    value.

    Beginning with OpenVMS Version 7.2, the default value has been
    raised to 575. The setting has been raised to accommodate the
    increased demands for process-permanent memory that result from
    changes made to RMS file-naming parsing in Version 7.2.

    This special parameter is used by HP and is subject to change. Do
    not change this parameter unless HP recommends that you do so.

    PIOPAGES is an AUTOGEN and DYNAMIC parameter.