Operating Systems versions prior to G06.24 do not provide the exact Operating System version as known by Users (i.e. G06.21) via supported system calls. You can determine the major portion (i.e. G06), but not the minor portion (i.e. .21).
The documented System procedure call PROCESSOR_GETINFOLIST_ has an item code defined to return the minor version number, but it always returns zero on systems prior to G06.24. To work around this limitation MOMI reads an undocumented file $SYSTEM.SYSNN.RLSEID. This file appears to be used by the utility SYSINFO and by TACL to obtain this information.
On Operating Systems G06.24 and later, the documented System procedure PROCESSOR_GETINFOLIST_ correctly returns the minor version number. The undocumented file $SYSTEM.SYSNN.RLSEID is not accessed.
The TNS/E Integrity System must use the RLSEID file. Hopefully, this may be removed in a future O/S release.