The system time is initialized during IPL by the TODR being loaded.
Time sources for system time initialization
The SVP time determined by the “Store Real Clock” interface is used as the time source for initialization.
The following special case also exists: The system is started in DIALOG mode with the UNLOCK option and the operator makes an explicit time specification.
The employed time source is logged as an insert in startup message NSI1163.
The setting for summer time/winter time is initialized by means of the SVP information. If the information is not available in SVP or if the time has been specified manually (by means of the UNLOCK option), it is not possible to unambiguously recognize a duplicated hour on summer time/winter time changeover. In this case, startup assumes winter time.
For information on initializing the system time, see also section "Determining the timesystem initialization".