[wpietri]

Agreed on most of that, but this is not always right: "cursing your predecessor for not having that foresight to realize that a number might grow beyond 999"

My dad was a COBOL developer in the 60s and 70s, and I asked him about this during the Y2K panic. Back then, the cost per byte was extremely high. Even if they had thought people would be foolish enough to keep systems running for decades, they still would have gone with 2 digits for the year because they needed those bits for other things.

Looking up the numbers now, in 1969 IBM was selling magnetic disk drives for circa $1/KB[1] at a time when programmers were making ~$200/week[2]. Top data speed was something like 300KB/s. The CPUs processing the data cost the equivalent of 5-10 programmer's salaries to rent. So throwing out the century, a 25% savings on date data storage, was a no-brainer. Not just for the tech people, but from a management perspective. Imagine asking, "How about we fire a couple of our developers so we can buy another drive and make sure this is easy to develop on 50 years from now?"

[1] https://www.ibm.com/ibm/history/exhibits/storage/storage_231...

[2] https://fraser.stlouisfed.org/title/industry-wage-survey-lif...