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The Year 2000 problem (also known as the Y2K problem, the millennium bug, the Y2K bug, or simply Y2K) was a notable problem for both digital (computer-related) and non-digital documentation and data storage situations which resulted from the practice of abbreviating a four-digit year to two digits.

In computer program design, the practice of representing the year with two digits becomes problematic with logical error(s) arising upon "rollover" from x99 to x00. This has caused some date-related processing to operate incorrectly for dates and times on and after January 1, 2000 and on other critical dates which were billed "event horizons". Without corrective action, it was suggested that long-working systems would break down when the "...97, 98, 99, 00..." ascending numbering assumption suddenly became invalid. Companies and organizations worldwide checked, fixed, and upgraded their computer systems.

While no globally significant computer failures occurred when the clocks rolled over into 2000, preparation for the Y2K bug had a significant effect on the computer industry. Countries that spent very little on tackling the Y2K bug (including Italymarker and South Koreamarker) experienced as few problems as those that spent much more (such as the United Kingdommarker and the United Statesmarker), causing some to question whether the absence of computer failures was the result of the preparation undertaken or whether the significance of the problem had been overstated.

Many banks have responded to the Y2K problem by forcing full 4-digit year entries on cheque forms, which helps to prevent the error from occurring in accounting environments.


Y2K was the common abbreviation for the year 2000 software problem. The abbreviation combines the letter Y for "year", and k for the Greek prefix kilo meaning 1000; hence, 2K signifies 2000. It was also named the Millennium Bug because it was associated with the popular, rather than literal, roll-over of the millennium, despite the fact that the bug could have occurred at the end of any ordinary century.

The Year 2000 problem was the subject of the early book, "Computers in Crisis" by Jerome and Marilyn Murray (Petrocelli, 1984; reissued by McGraw-Hill under the title "The Year 2000 Computing Crisis" in 1996). The first recorded mention of the Year 2000 Problem on a Usenet newsgroup occurred Saturday, January 19, 1985 by Usenet poster Spencer Bolles. Google Groups - net. bugs - " Computer bugs in the year 2000." Retrieved on 22 April 2007.

The acronym Y2K has been attributed to David Eddy, a Massachusetts programmer, in an e-mail sent on June 12, 1995. He later said, "People were calling it CDC (Century Date Change), FADL (Faulty Date Logic) and other names."

Many computer programs stored years with only two digits, for example, 1980 would be stored as 80. Some such programs could not distinguish between the year 2000 and the year 1900. Other programs would try to represent the year 2000 as 19100. This could cause a complete failure and cause date comparisons to produce incorrect results. Some embedded systems, making use of similar date logic, were expected to fail and cause utilities and other crucial infrastructure to fail.

Some warnings of what would happen if nothing were done were particularly dire:

Special committees were set up by governments to monitor remedial work and contingency planning, particularly by crucial infrastructures such as telecommunications, utilities and the like, to ensure that the most critical services had fixed their own problems and were prepared for problems with others. While some commentators and experts argued that the coverage of the bug largely amounted to scaremongering, it was only the safe passing of the main "event horizon" itself, January 1, 2000, that fully quelled public fears. Some experts who argued that scaremongering was occurring, such as Ross Anderson, Professor of Security Engineering at the University of Cambridge Computer Laboratorymarker, have since claimed that despite sending out hundreds of press releases about research results suggesting that the bug was not likely to be as big a problem as some had suggested, they were largely ignored by the media.

Programming problem

The practice of using two-digit dates for convenience predates computers.

The need for bit conservation

In the 1960s, computer memory was 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 these two digits for every date field was significant in the 1960s. Since programs at that time were mostly short-lived affairs programmed to solve a specific problem, or control a specific hardware setup, neither managers nor programmers of that time expected their programs to remain in use for many decades. The realization that databases were a new type of program with different characteristics had not yet come, and hence most did not consider fixing two digits of the year a significant problem.

There were exceptions, of course. The first person known to publicly address this issue was Bob Bemer, who had noticed it in 1958 as a result of work on genealogical software. He spent the next twenty years trying to make programmers, IBM, the US government and the ISO aware of the problem, with little result. This included the recommendation that the COBOL PICTURE clause should be used to specify four digit years for dates. This could have been done by programmers at any time from the initial release of the first COBOL compiler in 1961 onwards. However, lack of foresight, the desire to save storage space, and overall complacency prevented this advice from being followed. Despite magazine articles on the subject from 1970 onwards, the majority of programmers only started recognizing Y2K as a looming problem in the mid-1990s, but even then, inertia and complacency caused it to be mostly unresolved until the last few years of the decade. In 1989 Erik Naggum was instrumental in ensuring that internet mail used four digit representations of years by including a strong recommendation to this effect in the Internet host requirements document (RFC-1123).

Resulting bugs from date programming

Storage of a combined date and time within a fixed binary field is often considered a solution, but the possibility for software to misinterpret dates remains, because such date and time representations must be relative to a predefined origin. Rollover of such systems is still a problem but can happen at varying dates and can fail in various ways. For example:

  • The Microsoft Excel spreadsheet program had a very elementary Y2K problem: Excel (in both Windows versions and Mac version, when they are set to start at 1900) incorrectly set the year 1900 as a leap year, for compatibility with Lotus 1-2-3. In addition, the years 2100, 2200 and so on were regarded as leap years. This bug was fixed in later versions, but since the epoch of the Excel timestamp was set to the meaningless date of January 0 1900 in previous versions, the year 1900 is still regarded as a leap year to maintain backward compatibility.
  • In the C programming language, the standard library function to get the current year represents the year as year minus 1900. There were programmers who used C or a language using functions from C, such as Perl and Java, two programming languages widely used in web development, who incorrectly treated this value as the last two digits of the year since they hadn't read the specifications. On the web this usually was a harmless presentation bug, but it did cause many dynamically generated webpages to display January 1, 2000 as "1/1/19100", "1/1/100", or other variants, depending on the format.
  • JavaScript was changed due to the concerns of the Y2K bug, and the return value for years changed and thus differed between versions from sometimes being a four digit representation and sometimes a two-digit representation forcing programmers to rewrite already working code to make sure their webpages worked for all versions. This forced programmers to change already working code and add checks to see if the returned date was less than 1900 or not and act accordingly.
  • Older applications written for the commonly used UNIX source code control system SCCS failed to handle years that began with the digit "2".
  • In the Windows 3.x file manager, dates were shown as 1/1/19:0 for 1/1/2000 (because the colon is the character after 9 in the character set). An update was available.

Date bugs similar to Y2K

9 September 1999

Even before 1 January 2000 arrived, there were also some worries about 9 September 1999 (albeit lesser compared to those generated by Y2K). Because this date could also be written in the numeric format 9/9/99, it could have conflicted with the date value 9999, frequently used to specify an unknown date. It was thus possible that database programs might act on the records containing unknown dates on that day. Somewhat similar to this is the end-of-file code 9999, used in older programming languages. While fears arose that some programs might unexpectedly terminate on that date, the bug was more likely to confuse computer operators than machines.

Leap years

A year is a leap year if it is divisible by 4 but not divisible by 100 unless it is also divisible by 400. For example, 1600 was a leap year, but 1700, 1800 and 1900 were not. Most programs relied on the oversimplified rule that a year divisible by 4 is a leap year. Fortunately, this method works fine for the year 2000 (because it was a leap year), and will not become a problem until 2100, when hopefully older legacy programs will have long since been replaced.

Year 2038 problem

The typical Unix timestamp (time_t) stores a date and time as a 32-bit signed integer number representing, roughly speaking, the number of seconds since January 1, 1970; in 2038, this number will roll over (exceed 32 bits), causing the Year 2038 problem (also known as Unix Millennium bug, or Y2K38). To solve this problem, many systems and languages have switched to a 64-bit version, or supplied alternatives which are 64-bit.

Confusion between month and year

Ambiguity and errors can rise when different methods of ordering a Day/Month/Year sequence are used by different entities. For example, 30/11/05 could result in the interpretations of November 5, 2030; November 30, 2005, May 30, 2011, or even May 11, 2030. Any year abbreviated prior to 2031 can lead to the error. Attempting to standardize the date-ordering sequence (i.e. S.I., ISO) is not a feasible solution to the problem due to the open nature of writing, international differences, and human behaviour.

Programming solutions

Two very different approaches were used to solve the Year 2000 problem in legacy systems:

  • Date expansion: 2-digit years were expanded to include the century (becoming 4-digit years) in programs, files and databases. This was considered the "purest" solution, resulting in unambiguous dates that are permanent and easy to maintain. However, this method was costly, requiring massive testing and conversion efforts, and usually affecting entire systems.

  • Windowing: 2-digit years were retained, and programs determined the century value only when needed for particular functions, such as date comparisons and calculations. (The century "window" refers to the 100-year period to which a date belongs.) This technique, which required installing small patches of code into programs, was simpler to test and implement than date expansion, thus much less costly. While not a permanent solution, windowing fixes were usually designed to work for several decades. This was thought acceptable, as older legacy systems eventually get replaced by newer technology.

Documented errors

Before 2000

  • On 28 December 1999, 10,000 card swipe machines issued by HSBC and manufactured by Racal stopped processing credit and debit card transactions. The stores relied on paper transactions until the machines started working again on 1 January.

On 1 January 2000

When 1 January 2000 arrived, there were problems generally regarded as minor. Problems did not always have to occur precisely at midnight. Some programs were not active at that moment and would only show up when they were invoked. Not all problems recorded were directly linked to Y2K programming in a causality; minor technological glitches occur on a regular basis.

Reported problems include:

  • In Ishikawa, Japan, radiation-monitoring equipment failed at midnight, but officials said there was no risk to the public.
  • In Onagawa, Japan, an alarm sounded at a nuclear power plant at two minutes after midnight.
  • In Japan, at two minutes past midnight, Osaka Media Port, a telecommunications carrier, found errors in the date management part of the company's network. The problem was fixed by 02:43 and no services were disrupted.
  • In Japan, NTT Mobile Communications Network (NTT DoCoMo), Japan's largest cellular operator, reported on 1 January 2000, that some models of mobile telephones were deleting new messages received, rather than the older messages, as the memory filled up.
  • In Australia, bus-ticket-validation machines in two states failed to operate.
  • In the United Statesmarker, 150 slot machines at race tracks in Delawaremarker stopped working.
  • In the United Statesmarker, the U.S.marker Naval Observatorymarker, which runs the master clock that keeps the country's official time, had a Y2K glitch on its Web site. Due to a programming problem, the site reported that the date was Jan. 1, 19100.
  • In Francemarker, the national weather forecasting service, Meteo France, said a Y2K bug made the date on a webpage show a map with Saturday's weather forecast as "01/01/19100". This also occurred on other Web sites, including, at the time a general-purpose portal site primarily for AT&T Worldnet customers in the United States.

Government responses

United States

The United States Government responded to the Y2K threat by passing the Year 2000 Information and Readiness Disclosure Act, by working with private sector counterparts in order to ensure readiness, and by creating internal continuity of operations plans in the event of problems. The effort was coordinated out of the White House by the President's Council On Year 2000 Conversion, headed by John Koskinen. The White Housemarker effort was conducted in coordination with the then-independent Federal Emergency Management Agency (FEMA), and an interim Critical Infrastructure Protection Group, then in the Department of Justice, now in Homeland Security. The Dutch Government promoted Y2K Information Sharing and Analysis Centers (ISACs) to share readiness between industries, without threat of antitrust violations or liability based on information shared.

The US Government followed a three part approach to the problem: (1) Outreach and Advocacy (2) Monitoring and Assessment and (3) Contingency Planning and Regulation.

The logo created by The President's Council on the Year 2000 Conversion, for use on
A feature of US Government outreach was Y2K websites including Y2K.GOV. Presently, many US Government agencies have taken down their Y2K websites. Some of these documents may be available through National Archives and Records Administrationmarker or The Wayback Machine.

Each federal agency had its own Y2K task force which worked with its private sector counter parts. The FCC had the FCC Year 2000 Task Force.

Most industries had contingency plans that relied upon the Internet for backup communications. However, as no federal agency had clear authority with regard to the Internet at this time (it had passed from the US Department of Defense to the US National Science Foundation and then to the US Department of Commerce), no agency was assessing the readiness of the Internet itself. Therefore on July 30, 1999 the White House held the White House Internet Y2K Roundtable.

International cooperation

The International Y2K Cooperation Center (IY2KCC) was established at the behest of national Y2K coordinators from over 120 countries when they met at the First Global Meeting of National Y2K Coordinators at the United Nations in December 1988. IY2KCC established an office in Washington, D.C. in March 1999. Funding was provided by the World Bank, and Bruce W. McConnell was appointed as director.

IY2KCC's mission was to "promote increased strategic cooperation and action among governments, peoples, and the private sector to minimize adverse Y2K effects on the global society and economy." Activities of IY2KCC were conducted in six areas:

  • National Readiness: Promoting Y2K programs worldwide
  • Regional Cooperation: Promoting and supporting coordination within defined geographic areas
  • Sector Cooperation: Promoting and supporting coordination within and across defined economic sectors
  • Continuity and Response Cooperation: Promoting and supporting coordination to ensure essential services and provisions for emergency response
  • Information Cooperation: Promoting and supporting international information sharing and publicity
  • Facilitation and Assistance: Organizing global meetings of Y2K coordinators and to identify resources

IY2KCC closed down in March 2000.

Norway and Finland

Norway and Finland changed their National identification number, to indicate the century in which a person was born. Previously the birth year in both countries was indicated with two digits only. People born in the 20th century did not have to change their number. However, a similar problem already existed, the "Year 1900 problem", about distinguishing between people born in the 19th or 20th century, so the timing was more because of the Y2K attention than a solution to a new problem.

Private sector response

  • The United States established the Year 2000 Information and Readiness Disclosure Act, which limited the liability of businesses who had properly disclosed their Y2K readiness.
  • 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).
  • Survivalist-related businesses (gun dealers, surplus and sporting goods, LDS bookstores selling freeze-dried food) anticipated increased business in the final months of 1999. Some of these businesses experienced increased sales; some did not.
  • The Long Now Foundation, which (in their words) "seeks to promote 'slower/better' thinking and to foster creativity in the framework of the next 10,000 years", has a policy of anticipating the Year 10,000 problem by writing all years with five digits. For example, they list "01996" as their year of founding.
  • While there was no one comprehensive Internet Y2K effort, multiple Internet trade associations and organizations banded together to form the Internet Year 2000 Campaign. This effort partnered with the White House's Internet Y2K Roundtable.

The Y2K issue was a major topic of discussion in the late 1990s and, predictably, showed up in most popular media. A number of "Y2K disaster" books were published such as Deadline Y2K by Mark Joseph. Movies such as Y2K: Year to Kill capitalized on the currency of Y2K, as did numerous TV shows, comic strips, and computer games.


The total cost of the work done in preparation for Y2K is estimated at over 300 billion US dollars. There are two ways to view the events of 2000 from the perspective of its aftermath:

Supporting view

This view holds that the vast majority of problems had been fixed correctly, and the money was well spent. The situation was essentially one of preemptive alarm. Those who hold this view claim that the lack of problems at the date change reflect the completeness of the project, and that many computer applications would not have continued to function into the 21st century without correction or remediation.

  • This view was adopted by most of the (fairly limited) official examinations of Y2K projects undertaken after their completion.
  • It has also been suggested that on September 11, 2001, the New York infrastructure (including subways, phone service, and financial transactions) were able to continue operation because of the redundant networks established in the event of Y2K bug impact and the contingency plans devised by companies. The terrorist attacks and the following prolonged blackout to lower Manhattan had minimal effect on global banking systems. Backup systems were activated at various locations around the region, many of which had been established to deal with a possible complete failure of networks in the financial district on December 31, 1999. Had the emphasis on creating backup systems to deal with Y2K not occurred, much greater disruption to the economy could have occurred. Decentralization of infrastructure — in particular, the creation of multiple sites for backup data — helped keep banks up and running.
  • It was suggested that Y2K plans were used to ground aircraft on 9/11, but the grounding was a variant of the SCATANA procedures developed in 1958..

Opposing view

Others have claimed that there were no, or very few, critical problems to begin with, and that correcting the few minor mistakes as they occurred (the 'fix on failure' approach) would have been the most efficient and cost effective way to solve the problem. Editorial writing in the Wall Street Journal called Y2K an end-of-the-world cult and the hoax of the century. The opposing view was bolstered by a number of observations.

  • The lack of Y2K-related problems in schools, many of which undertook little or no remediation effort. By September 1, 1999 only 28 percent of US schools had achieved compliance for mission critical systems, and a government report predicted that "Y2K failures could very well plague the computers used by schools to manage payrolls, student records, online curricula, and building safety systems".
  • The lack of Y2K-related problems in an estimated 1.5 million small businesses that undertook no remediation effort. On 3 January 2000 (the first weekday of the year) the Small Business Administration received an estimated 40 calls from businesses with computer problems, similar to the average. None of the problems were critical.
  • The lack of Y2K-related problems in countries such as Italymarker, which undertook a far more limited remediation effort than the United States. In an October 22, 1999, report, a US Senate Committee expressed concern about safe travel outside of the United States. The report stated that overseas public transit systems were considered vulnerable because many did not have an aggressive response plan in place for any problems. Internationally, the report singled out Italy, Chinamarker and Russiamarker as poorly prepared. The Australian government evacuated all but three embassy staff from Russia. None of these countries experienced any Y2K problems regarded as worth reporting.
  • The absence of Y2K-related problems occurring before January 1, 2000, even though the 2000 financial year commenced in 1999 in many jurisdictions, and a wide range of forward-looking calculations involved dates in 2000 and later years. Estimates undertaken in the leadup to 2000 suggested that around 25% of all problems should have occurred before 2000. Critics of large-scale remediation argued, during 1999, that the absence of significant problems, even in systems that had not been rendered compliant, suggested that the scale of the problem had been severely overestimated.

See also


  1. American RadioWorks Y2K Notebook Problems - The Surprising Legacy of Y2K. Retrieved on 22 April 2007.
  2. "Requirements for Internet Hosts -- Application and Support"
  3. Microsoft Knowledge Base article 214326
  4. Stockton, J.R., " Critical and Significant Dates" Merlyn
  5. "The Case for Windowing: Techniques That Buy 60 Years", article by Raymond B. Howard, Year/2000 Journal, Mar/Apr 1998.
  6. Millennium bug hits retailers, from BBC News, 29 December 1999
  7. Y2K bug fails to bite, from BBC News, 1 January 2000
  8. Computer problems hit three nuclear plants in Japan, report by Martyn Williams of CNN, 3 January 2000
  9. Minor bug problems arise, report from BBC News, 1 January 2000
  10. BBC NEWS | Science/Nature | Minor bug problems arise
  11. Preparation pays off; world reports only tiny Y2K glitches, report by Marsha Walton and Miles O'Brien of CNN, 1 January 2000
  12. White House shifts Y2K focus to states, CNN (Feb. 23, 1999)
  13. See President Clinton: Addressing the Y2K Problem, White House, Oct. 19, 1998
  14. Federal Communications Commission Spearheads Oversight of the U.S. Communications Industries' Y2K Preparedness, Wiley, Rein & Fielding Fall 1999
  15. International Y2K Cooperation Center Records, Charles Babbage Institute
  16. Internet Year 2000 Campaigned archived at Cybertelecom
  17. Y2K: Overhyped and oversold?, report from BBC News, 6 January 2000
  18. Department of State Washington File: Transcript: What Happened to Y2K? Koskinen Speaks Out
  19. Y2K readiness helped New York after 9/11, article by Lois Slavin of MIT News, 20 November 2000
  20. September 11 and the U.S. Payment System, article by Christine M. Cumming of the International Monetary Fund
  21. Y2K readiness helped NYC on 9/11, article by Rae Zimmerman of MIT News, 19 November 2000
  22. Plan for the Security Control of Air Traffic and Air Navigation Aids (Short Title: SCATANA), April 1980
  23. .
  24. White House: Schools lag in Y2K readiness: President's Council sounds alarm over K-12 districts' preparations so far, article by Jonathan Levine of eSchool News, 01 September 1999
  25. Most small businesses win their Y2K gamble, article by Kent Hoover, 10 January 2000
  26. Y2K travel warning issued, report by Fiona Reynolds of ABC Radio, 1 December 1999
  27. Fight or Flight?: Assessing Your Y2K Travel Risks, article by Tracy Davis of Boston College, 1999
  28. Lights out? Y2K appears safe, article by Elizabeth Weise of USA Today, 14 February 1999
  29. Y2K bug may never bite, article by John Quiggin of the Australian Financial Review, 02 September 1999

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