The Year 2000 Problem was a flaw in computer program design that caused some date-related processing to operate incorrectly for dates and times after January 1, 2000. It turned into a media-hype-driven societal fear that critical industries (electricity, financial, etc.) would stop working at 12:00 AM, January 1, 2000.
It was thought computer programs could stop working or produce erroneous results because they stored years with only two digits and that the year 2000 would be represented by '00' and would not follow 1999 (i.e., '99') in numerical sequence. This would cause date comparisions to produce incorrect results.
The underlying programming problem was quite real. In the 1960s, computer memory and storage were scarce and expensive, and most data processing was done on punch cards which represented text data in 80-column records. Programming languages of the time, such as COBOL and RPG, processed numbers in their ASCII or EBCDIC representations. They occasionally used an extra bit called a "zone punch" to save one character for a minus sign on a negative number, or compressed two digits into one byte in a form called binary-coded decimal, but otherwise processed numbers as straight text. Over time the punch cards were converted to magnetic tape and then disk files and later to simple databases like ISAM, but the structure of the programs usually changed very little. Popular software like dBase continued the practice of storing dates as text well into the 1980s and 1990s.
Saving two characters for every date field was a significant savings at that time. Most programmers of that day did not expect their programs to remain in use for many decades, so it was not considered a significant problem. Programmers started recognizing it as a looming problem in the 1980s, but inertia and apathy caused it to be mostly ignored.
Storage of a combined date and time within a fixed binary field is often considered a solution, but the possibility for software to mis-interpret dates remains, because such date and time representations must be relative to a defined origin. Roll-over of such systems is still a problem but can happen at varying dates and can fail in various ways. For example:
- The typical Unix timestamp stores a date and time as a 32-bit integer number representing the number of seconds since January 1, 1970, and will roll over in 2038. See Unix epoch.
- The popular spreadsheet Microsoft Excel stores a date as a number of days since an origin (often called a Julian date). A Julian date stored in a 16-bit integer will overflow after approximately 179 years (i.e. 65,536 days). Unfortunately, some releases of the program start at 1900, others at 1904).
- When a program written in the Perl programming language looks up the current year, it receives the year minus 1900. Many careless programmers incorrectly treated this value as the last two digits of the year. This mostly harmless bug caused many dynamically generated webpages to display January 1, 2000, as "1/1/19100".
Another related problem for the year 2000 was that it was a leap year even though years ending in '00' are normally not leap years. (A year is a leap year if it is divisible by 4 unless it is both divisible by 100 and not divsible by 400.)
Some industries started experiencing related problems early in the 1990s as software began to process future dates past 1999. For example, in 1993, some people with financial loans that were due in 2000 received (incorrect) notices that they were 93 years past due. As the decade progressed, more and more companies experienced problems and lost money due to erroneous date data. As another example, meat-processing companies incorrectly destroyed large amounts of good meat because the computerized inventory system identified the meat as expired.
As the decade progressed, identifying and correcting or replacing affected computer systems or computerized devices became the major focus of information technology departments in most large companies and organizations. Millions of lines of programming code were reviewed and fixed during this period. Many corporations replaced major software systems with completely new ones that did not have the date processing problems.
Y2K was the big media hype story of 1999. Public apprehension was tremendous, reaching mythical proportions. Some individuals stockpiled canned food in anticipation of food shortages. Some extreme commentators predicted a full-scale apocalypse. But when January 1, 2000 finally came, there were hardly any major problems, though a large number of them had been expected. Ironically, many people were upset that there appeared to be so much hype over nothing, because the vast majority of problems had been fixed correctly. Some more sophisticated critics have suggested that much preventative effort was unnecessary -- it would have been cheaper not to spend as much examining non-critical systems for flaws and simply fix the few that would have failed after the event. Such conclusions are easy to draw with the benefit of hindsight, but in any case the overhaul of many systems involved replacement with new, improved functionality anyway and thus in many cases the expenditure proved useful regardless.
Some items of interest:
- Insurance companies sold insurance policies covering failure of businesses due to Y2K problems.
- Attorneys organized and mobilized for Y2K class action lawsuits (which were not pursued).
- No major failures of infrastructure were reported in the United States.
- The Y2K problem mainly affected countries that follow the western calendar (China and Saudi Arabia do not).
- One theory has it that the Federal Reserve increased the money supply in 1999 to compensate for anticipated hording by a frightened populace. The populace, however, was not frightened, and the flood of new money fueled a stock market high tide that went out in spring of 2000.
- Many organisations finally realised the critical importance of their IT infrastructure to their business, and put in place plans to keep it running and restore capability in case of disaster. Such planning may well have helped the relatively speedy return to functioning of New York's critical financial IT systems after the September 11, 2001 terrorist attack.
- Speculatively, the Y2K spending on information infrastructure caused a slowdown in information technology spending in the year 2000 and 2001 as may eventually lead to higher productivity in future years.