z/OS UNIX System Services is set up, in part, using members in the PARMLIB concatenation. These members are prefixed BPXPRM and have user-specified suffixes. One or more BPXPRMxx members are selected at initial program load (IPL). MVS operator commands allow the members in use to be changed at any time and allow many individual parameters to be overridden at any time.
The active values for parameters may not match those in the active members for two reasons: members being edited but not activated, and overrides by operator command.