1987
I'm reminded of a presentation at uni at the time by Head of IT for the ASX Australian Stock Exchange.
It went fully electronic (first in the world) in 1987, in an all-or-nothing big-bang overnight Live cutover. Same day, the global market crashed — Australia, Singapore, and Hong Kong by 40%.
He was somewhere between quietly proud and chuffed when he said he likes to say re the project: "The market crashed but we didn't."