On Tue, 2 Nov 2021 15:06:04 +0100, Stefan Skoglund <[email protected]> wrote:
>my point was that UTC doesnt change one whole hour in a leap. UTC is not a time zone . Its value changes only when leap seconds are introduced. >IF two different people in different timezones installs each their own >z15, if they push return at exactly the same time. What time >will the HMC expect the computer to be in ? (sort of.) The HMC has no expectations about the TOD clock of a CPC. If you don't have the STP feature, a POR will set the TOD clock according to the SE. If you have the STP feature, the SE will set its time to STP time (better clock!). Architecturally, the TOD clock follows TAI, with an epoch (TOD = all zeros) of Jan 1, 1900. It doesn't care about the 37 leap seconds that have been introduced into UTC since the epoch.(hence, TAI) If you used a standard TOD-to-civil time conversion (which all assume TOD is UTC), the result would be 37 seconds ahead of UTC. If the system is leap second-aware, then it subtracts the leap seconds when generating civil time. TAI -> UTC -> local time. When you don't configure leap seconds, the old (and new) algorithms will generate the correct civil time, but the observant person will discern that the epoch has moved 37 seconds backward into December 31, 1899. (And with each subsequent leap second, it moves backward an additional second.) Alan Altmark IBM ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
