… and I suspect today is going to be a busy day.

Back in the day, when I was working with mainframes, we would have to “stop” the mainframe at the end of daylight saving.

And wait an hour.

Why?

Transaction time-stamping is the reason.  The mainframe would happily stamp transactions will this:
02:00:00 Transaction 1
02:00:01 Transaction 2
02:00:02 Transaction 3

And once we get to 3am, and changed the time back to 2am, the mainframe would start overwriting the previous 02:00 transactions
02:00:00 Transaction 671
02:00:01 Transaction 672
02:00:02 Transaction 3

So we stopped the mainframe for an hour.

Nowadays, I expect that IBM mainframes would write transaction times in GMT UTC, which gets around the message overwriting issues.

Of course, Microsoft & Palm PDAs will have issues, and therefore I expect today will be a busy day.

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