There was no year zero, and common calendars begun in 1 A.D. Y2K had nothing to do with centuries and passage of time. Y2K’s problem was the computer calendar saw the year in two digits (1980 was interpreted as 80 by the computer), or in the format MM-DD-YY for those of us in the United States and DD-MM-YY elsewhere (and military installations). The year 2000 meant that the year according to the computer would be 1900 (more accurately it would have reverted back to the year the computer chip was made). Chip makers now create computer chips with 4 places for the year (YYYY) instead of two. Computers would continue to work fine, it was just the parts of the system that involved the passage of time that would see problems.