Why was Y2K specifically a big deal if computers actually store their numbers in binary? Why would a significant decimal date have any impact on a binary number?

Question

I understand the number would have still overflowed *eventually* but why was it specifically new years 2000 that would have broken it when binary numbers don’t tend to align very well with decimal numbers?

EDIT: A lot of you are simply answering by explaining what the Y2K bug is. I am aware of what it is, I am wondering specifically why the number ’99 (`01100011` in binary) going to 100 (`01100100` in binary) would actually cause any problems since all the math would be done in binary, and decimal would only be used for the display.

EXIT: Thanks for all your replies, I got some good answers, and a lot of unrelated ones (especially that one guy with the illegible comment about politics). Shutting off notifications, peace ✌

In: 478

Answer 1

Since as of this writing, the top comment doesn’t explain what’s being asked. In a lot of systems, years weren’t stored as binary numbers. Instead they were stored as two ascii characters.

So “99” is 0x39, 0x39 or 0011 1001 0011 1001 while “2000” would be 0011 0010 0011 0000 0011 0000 0011 0000. Notice that the second one takes more bytes to store.