Year 2000 problem

The term year 2000 problem, or simply Y2K, refers to potential computer errors related to the formatting and storage of calendar data for dates in and after the year 2000. Many programs represented four-digit years with only the final two digits, e.g. 1985 as 85, making the year 2000 indistinguishable from 1900. Computer systems' inability to distinguish dates correctly had the potential to bring down worldwide infrastructures for computer-reliant industries.
In the years leading up to the turn of the millennium, the public gradually became aware of the "Y2K scare", and individual companies predicted the global damage caused by the bug would require anything between $400 billion and $600 billion to rectify. A lack of clarity regarding the potential dangers of the bug led some to stock up on food, water, and firearms, purchase backup generators, and withdraw large sums of money in anticipation of a computer-induced apocalypse.
Contrary to published expectations, few major errors occurred in 2000. Supporters of the Y2K remediation effort argued that this was primarily due to the pre-emptive action of many computer programmers and information technology experts. Companies and organizations in some countries, but not all, had checked, fixed, and upgraded their computer systems to address the problem. The U.S. president Bill Clinton, who organized efforts to minimize the damage in the United States, labelled Y2K as "the first challenge of the 21st century successfully met", and retrospectives on the event typically commend the programmers who worked to avert the anticipated disaster.
Critics argued that even in countries where very little had been done to ready software, problems were minimal. The same was true in sectors such as schools and small businesses, where compliance with Y2K policies was inconsistent at best.

Background

Y2K is a numeronym and was the common abbreviation for the year 2000 software problem. The abbreviation combines the letter Y for "year", the number 2 and a capitalized version of 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 rollover of the millennium, even though most of the problems could have occurred at the end of any century.
Computerworlds 1993 three-page "Doomsday 2000" article by Peter de Jager was called "the information-age equivalent of the midnight ride of Paul Revere" by The New York Times.
The problem was the subject of the early book Computers in Crisis by Jerome and Marilyn Murray. Its first recorded mention on a Usenet newsgroup is from 18 January 1985, by Spencer Bolles.
The acronym Y2K has been attributed to Massachusetts programmer David Eddy in an e-mail sent on 12 June 1995. He later said, "People were calling it CDC, FADL. There were other contenders. Y2K just came off my fingertips."
The problem started because on both mainframe computers and later personal computers, memory was expensive, from as low as $10 per kilobyte to more than US$100 per kilobyte in 1975. It was therefore very important for programmers to minimize usage. Since computers only gained wide usage in the 20th century, programs could simply prefix "19" to the year of a date, allowing them to only store the last two digits of the year instead of four. As space on disc and tape storage was also expensive, these strategies saved money by reducing the size of stored data files and databases in exchange for becoming unusable past the year 2000.
This meant that programs facing two-digit years could not distinguish between dates in 1900 and 2000. Dire warnings at times were in the mode of:

The Y2K problem is the electronic equivalent of the El Niño and there will be nasty surprises around the globe.
Options on the De Jager Year 2000 Index, "the first index enabling investors to manage risk associated with the ... computer problem linked to the year 2000" began trading mid-March 1997.
Special committees were set up by governments to monitor remedial work and contingency planning, particularly by crucial infrastructures such as telecommunications, 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 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 as some had suggested, they were largely ignored by the media. In a similar vein, the Microsoft Press book Running Office 2000 Professional, published in May 1999, accurately predicted that most personal computer hardware and software would be unaffected by the year 2000 problem. Authors Michael Halvorson and Michael Young characterized most of the worries as popular hysteria, an opinion echoed by Microsoft Corp.
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.
Bit conservation need
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 kilobytes 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 disc 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, and the possibility that these programs would both remain in use and cause problems when interacting with databases – a new type of program with different characteristics – went largely uncommented upon.
Early attention
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 fruitlessly trying to raise awareness of the problem with programmers, IBM, the government of the United States and the International Organization for Standardization. This included the recommendation that the COBOL picture clause should be used to specify four digit years for dates.
In the 1980s, the brokerage industry began to address this issue, mostly because of bonds with maturity dates beyond the year 2000. By 1987 the New York Stock Exchange had reportedly spent over $20 million on Y2K, including hiring 100 programmers.
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. On April Fools' Day 1998, some companies set their mainframe computer dates to 2001, so that "the wrong date will be perceived as good fun instead of bad computing" while having a full day of testing.
While using 3-digit years and 3-digit dates within that year was used by some, others chose to use the number of days since a fixed date, such as 1 January 1900. Inaction was not an option, and risked major failure. Embedded systems with similar date logic were expected to malfunction and cause utilities and other crucial infrastructure to fail.
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, which causes the similar Y2K38 problem.
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:
Credit card systems experienced issues with machines not correctly processing credit cards that expired in the new millennium and customers being charged incorrect compound interest. An upscale grocer's 1997 credit-card caused a crash of their 10 cash registers, repeatedly, due to year 2000 expiration dates, and was the source of the first Y2K-related lawsuit.
The Microsoft Excel spreadsheet program had a very elementary Y2K problem: Excel 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.
The C programming language's standard library's date and time handling header defines a struct type whose year member represents the year minus 1900. Perl's and functions, derived from their C equivalents, as well as Java's class's method treat the year the same way. This led to a "popular misconception" that these functions returned the year as a two-digit number. Many programs written in Perl or 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 concerns over 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.
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. 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", and so on, depending on the last two digits of the present year.