Y2K problem

The Year 2000 problem (also known as the Y2K problem, the Millennium bug, the Y2K bug, or simply Y2K) was a 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 1997, The British Standards Institute (BSI) developed a standard, DISC PD2000-1, which defines "Year 2000 Conformity requirements" as four rules:
 * 1) No valid date will cause any interruption in operations.
 * 2) Calculation of durations between, or the sequence of, pairs of dates will be correct whether any dates are in different centuries.
 * 3) In all interfaces and in all storage, the century must be unambiguous, either specified, or calculable by algorithm
 * 4) Year 2000 must be recognized as a leap year

It identifies two problems that may exist in many computer programs.

Firstly, 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 1 January 2000, and on other critical dates which were billed "event horizons". Without corrective action, long-working systems would break down when the "... 97, 98, 99, 00 ..." ascending numbering assumption suddenly became invalid.

Secondly, some programmers had misunderstood the rule that determines whether years that are exactly divisible by 100 are leap years, and assumed the year 2000 would not be a leap year. Although most years divisible by 100 are not leap years, if they are divisible by 400 then they are. Thus the year 2000 was a leap year.

Companies and organizations worldwide checked, fixed, and upgraded their computer systems.

The number of computer failures that occurred when the clocks rolled over into 2000 in spite of remedial work is not known; amongst other reasons is the reticence of organisations to report problems.

Background
Y2K is a numeronym and was the common abbreviation for the year 2000 software problem. The abbreviation combines the letter Y for "year", and k for the SI unit 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, even though the problem 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 Friday, 18 January 1985, by Usenet poster Spencer Bolles.

The acronym Y2K has been attributed to David Eddy, a Massachusetts programmer, in an e-mail sent on 12 June 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 decimal 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 was done were particularly dire:

"The Y2K problem is the electronic equivalent of the El Niño and there will be nasty surprises around the globe. — John Hamre, United States Deputy Secretary of Defense"

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 problem largely amounted to scaremongering, it was only the safe passing of the main "event horizon" itself, 1 January 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 Laboratory, have since claimed that despite sending out hundreds of press releases about research results suggesting that the problem 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, but was never a problem until stored dates were used in calculations.

The need for bit conservation
In the first half of the 20th century, well before the computer era, business data processing was done using unit record equipment and punched cards, most commonly the 80-column variety employed by IBM, which dominated the industry. Many tricks were used to squeeze needed data into fixed-field 80-character records. Saving two digits for every date field was significant in this effort.

In the 1960s, computer memory and mass storage were scarce and expensive. Early core memory cost one dollar per bit. Popular commercial computers, such as the IBM 1401, shipped with as little as 2 Kbytes of memory. Programs often mimicked card processing techniques. Commercial programming languages of the time, such as COBOL and RPG, processed numbers in their character representations. Over time the punched cards were converted to magnetic tape and then disk files, but the structure of the data usually changed very little. Data was still input using punched cards until the mid-1970s. Machine architectures, programming languages and application designs were evolving rapidly. 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.

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 U.S. 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. Despite magazine articles on the subject from 1970 onward, the majority of programmers and managers 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.

Saving space on stored dates persisted into the Unix era, with most systems representing dates to a single 32-bit word, typically representing dates as elapsed seconds from some fixed date.

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 some known 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 and Mac versions, 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 0 January 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 extract the year from a timestamp returns the year minus 1900. Many programs using functions from C, such as Perl and Java, two programming languages widely used in web development, incorrectly treated this value as the last two digits of the year. On the web this was usually a harmless presentation bug, but it did cause many dynamically generated web pages to display 1 January 2000 as "1/1/19100", "1/1/100", or other variants, depending on the display 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 web pages 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 and react accordingly.
 * Older applications written for the commonly used UNIX Source Code Control System failed to handle years that began with the digit "2".
 * In the Windows 3.x file manager, dates displayed as 1/1/19:0 for 1/1/2000 (because the colon is the character after "9" in the ASCII character set). An update was available.
 * Some software, such as Math Blaster Episode I: In Search of Spot which only treats years as two-digit values instead of four, will give a given year as "1900", "1901", as so on, depending on the last two digits of the present year.

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, 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. Data-entry operators commonly entered 9999, into required-fields for an unknown future-date, (e.g. a termination date for cable-television or telephone service), in order to process computer forms using CICS software. Somewhat similar to this is the end-of-file code, 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
Mostly, a year is a leap year if it is evenly divisible by four. A year divisible by 100, however, is not a leap year on the Gregorian calendar unless it is also divisible by 400. For example, 1600 was a leap year, but 1700, 1800 and 1900 were not. Some programs may have relied on the oversimplified rule that a year divisible by four is a leap year. This method works fine for the year 2000 (because it is a leap year), and will not become a problem until 2100, when older legacy programs will likely have long since been replaced. Other programs contained incorrect leap year logic, assuming for instance that no year divisible by 100 could be a leap year. An assessment of this leap year problem including a number of real life code fragments appeared in 1998. For information on why century years are treated differently, see Gregorian calendar.

Year 2010 problem
Some systems had problems once the year rolled over to 2010. This was dubbed by some in the media as the "Y2K+10" or "Y2.01k" problem.

The main source of problems was confusion between hexadecimal number encoding and Binary-coded decimal encodings of numbers. Both hexadecimal and BCD encode the numbers 0–9 as 0x0–0x9. But BCD encodes the number 10 as 0x10, whereas hexadecimal encodes the number 10 as 0x0A; 0x10 interpreted as a hexadecimal encoding represents the number 16.

For example, because the SMS protocol uses BCD for dates, some mobile phone software incorrectly reported dates of SMSes as 2016 instead of 2010. Windows Mobile is the first software reported to have been affected by this glitch; in some cases WM6 changes the date of any incoming SMS message sent after 1 January 2010 from the year "2010" to "2016".

Other systems affected include EFTPOS terminals, and the PlayStation 3 (except the Slim model).

The most important occurrence of such a glitch was in Germany, where upwards of 20 million bank cards became unusable, and with Citibank Belgium, whose digipass customer identification chips failed.

Year 2038 problem
The original Unix timestamp datatype stores a date and time as a signed 32-bit integer representing the number of seconds since 1 January 1970. During and after 2038, this number will exceed 2$31$ − 1, the largest number representable by a signed 32-bit integer, causing the Year 2038 problem (also known as the Unix Millennium bug or Y2K38). To solve this problem, many systems and languages have switched to a 64-bit timestamp or supplied 64-bit alternatives.

Programming solutions
Several very different approaches were used to solve the Year 2000 problem in legacy systems. Three of them follow:
 * Date expansion: Two-digit years were expanded to include the century (becoming four-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.
 * Date re-partitioning: In legacy databases whose size could not be economically changed, six-digit year/month/day codes were converted to three-digit years (with 1999 represented as 099 and 2001 represented as 101, etc.) and three-digit days (ordinal date in year). Only input and output instructions for the date fields had to be modified, but most other date operations, and whole record operations required no change. This delays the eventual roll-over problem to the end of the year 2899.
 * Windowing: Two-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 tend to eventually get replaced by newer technology.

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. Consequences did not always result 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. Some caused erroneous results, some caused machines to stop working, some caused date errors, and two caused malfunctions.

Reported problems include:


 * In Sheffield, United Kingdom, incorrect Down syndrome test results were sent to 154 pregnant women and two abortions were carried out as a direct result of a Y2K bug. Four Down's syndrome babies were also born to mothers who had been told they were in the low-risk group.
 * In Ishikawa, Japan, radiation-monitoring equipment failed at midnight; however, officials stated 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 States, 150 slot machines at race tracks in Delaware stopped working.
 * In the United States, the U.S. Naval Observatory, which runs the master clock that keeps the country's official time, gave the date on its website as 1 Jan., 19100.
 * In France, 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 websites, including att.net, at the time a general-purpose portal site primarily for AT&T Worldnet customers in the United States.

Bulgaria
Although only two digits are allocated for the birth year in the Bulgarian national identification number, the year 1900 problem and subsequently the Y2K problem were addressed by the use of unused values above 12 in the month range. For all persons born before 1900, the month is stored as calendar month + 20, and for all persons born after 1999, the month is stored as calendar month + 40.

Uganda
The Uganda Government responded to the Y2K threat by setting up a Y2K Task Force. In August 1999 an independent international assessment by the World Bank International Y2k Cooperation Centre found that Uganda's website was in the top category as "highly informative". This put Uganda in the "top 20" out of 107 national governments, and on a par with the United States, United Kingdom, Canada, Australia and Japan, and ahead of Germany, Italy, Austria, Switzerland which were rated as only "somewhat informative". The report said that "Countries which disclose more Y2k information will be more likely to maintain public confidence in their own countries and in the international markets."

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

A feature of U.S. Government outreach was Y2K websites including Y2K.GOV. Presently, many U.S. Government agencies have taken down their Y2K websites. Some of these documents may be available through National Archives and Records Administration or the Wayback Machine.

Each federal agency had its own Y2K task force which worked with its private sector counterparts. 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 U.S. Department of Defense to the U.S. National Science Foundation and then to the U.S. Department of Commerce), no agency was assessing the readiness of the Internet itself. Therefore on 30 July 1999, the White House held the White House Internet Y2K Roundtable.

Norway and Finland
Norway and Finland changed their National identification number, to indicate the century in which a person was born. In both countries the birth year was indicated with two digits only. However, a similar problem already existed, the "Year 1900 problem", about distinguishing between people born in the 20th or 19th century, so the timing was more because of the Y2K attention than a solution to a new problem. In Finland the problem was solved by replacing the hyphen (" - ") in the number with the letter "A" for people born in the 21st century. In Norway, the range or the individual numbers following the birth date was altered from 0–499 to 500–999.

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.

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, Latter Day Saints bookstores selling freeze-dried food) anticipated increased business in the final months of 1999 in an event known as the Y2K scare.
 * 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 as such 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.

Cost
The total cost of the work done in preparation for Y2K is estimated at over US$300 billion ($ billion today, once inflation is taken into account ). IDC calculated that the U.S. spent an estimated $134 billion ($ billion) preparing for Y2K, and another $13 billion ($ billion) fixing problems in 2000 and 2001. Worldwide, $308 billion ($ billion) was estimated to have been spent on Y2K remediation. 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 reflects the completeness of the project, and that many computer applications would not have continued to function into the 21st century without correction or remediation.
 * Expected problems that were not seen by small businesses and small organizations were in fact prevented by Y2K fixes embedded in routine updates to operating system and utility software that were applied several years before 31 December 1999.
 * The extent to which larger industry and government fixes averted issues that would have more significant impacts had they not been fixed, were typically not disclosed or widely reported.
 * It has also been suggested that on 11 September 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 31 December 1999.

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". This 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 1 September 1999, only 28% of U.S. 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 Italy, which undertook a far more limited remediation effort than the United States. In a 22 October 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, China and Russia 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 1 January 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.