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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 problem for both digital (computer-related) and non-digital documentation and data storage situations that resulted from the practice of truncating a four-digit year to two digits. This made year 2000 indistinguishable from 1900. The former assumption that a twentieth-century date was always understood caused various errors concerning, in particular, the display of dates and the automated ordering of dated records or real-time events. In 1997, the British Standards Institute (BSI) developed a standard, DISC PD2000-1,〔(BSI Standard ), on year 2000〕 which defines "Year 2000 Conformity requirements" as four rules: # No valid date will cause any interruption in operations. # Calculation of durations between, or the sequence of, pairs of dates will be correct whether any dates are in different centuries. # In all interfaces and in all storage, the century must be unambiguous, either specified, or calculable by algorithm. # 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 Gregorian rule that determines whether years that are exactly divisible by 100 are not leap years, and assumed the year 2000 would not be a leap year. Although 3 out of 4 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; among other reasons is the reluctance 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,〔(American RadioWorks ) (Y2K Notebook Problems ) – ''(The Surprising Legacy of Y2K )''. Retrieved on 22 April 2007.〕 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 was stored as 80. Some such programs could not distinguish between the year 2000 and the year 1900. Other programs tried 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''〔(Looking at the Y2K bug ), portal on CNN.com〕 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.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Year 2000 problem」の詳細全文を読む スポンサード リンク
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