Y2K problem
The Y2K problem was identified in the late 1990s by computer scientists who observed that too many dates were stored with two-digit years. This leads to the critical problem of deciding whether, for example, a date recording as "12/25/80" refers to Christmas 1880 or Christmas 1980.
A two-digit year is recorded by leaving out the first two digits, seen as redundant. For systems which use only a short range of dates, say 1960 through 1990, this seemed to make sense. An event which took place in '75 could not have occurred in 2075 (far in the future) or in 1875 (the distant past). With memory as expensive as it was in the early days of modern computing, it was a common practice to save storage space by using two-digit years.
For birth dates, one can generally assume that most people live less than 80 years. So, for all practical purposes, it was possible to guess the century of their birth. In 1995, a person with a birth year of '55 could not have been born in 1855.[1]
As the years stretched on, however, more and more people were slipping through the cracks of this principle. Computer programmers began to wonder they could determine the age of someone born in '98 when runnning a report in the year 2001. Would it indicate a toddler or a centenarian? Clearly, something had to be done.
There are varying estimates of the total costs related to performing hardware and software analysis, remediation and testing related to the Y2K issue. Some estimates in the late 1990's put the worldwide cost in the trillions of dollars, but this has been dismissed as hyperbole. A typical exaggeration was counting hardware/software upgrades that happened to be Y2K-compliant as Y2K-related expenditures, when they would have taken place anyway. A more accurate estimate of the truly Y2K-driven analysis and cleanup effort would be in the tens of billions of dollars.[2]