And we still use 2 digit years! For example, credit cards often use the mm/yy format for expiration dates because it is more convenient to write and considerin

And we still use 2 digit years! For example, credit cards often use the mm/yy format for expiration dates because it is more convenient to write and considering the usual lifetime of a credit card, it is sufficient. But it means there is a two digit date somewhere in the system, and if the conversion just adds 2000, we are going to have a problem in 2100 if nothing changes, no matter how many bytes we use to represent and store the date. A lot of the Y2K problem was simple UI problems, like a text field with only 2 characters and a hardcoded +1900. One of the very few Y2K bugs I personally experienced was an internet forum going from the year 1999 to the year 19100. Somehow, they had the correct year (2000), subtracted 1900 (=100) and put a "19" in front as a string. Nothing serious, it was just a one-off display error, but that's the kind of thing that happened in Y2K, it wasn't just outdated COBOL software and byte savings.