Year 2000 problem

The Year 2000 problem (also known as the Y2K problem, the millennium bug, the Y2K bug, or simply Y2K) was a notable computer bug resulting from the practice in early computer program design of representing the year with two digits. This 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". This fear was fueled by the attendant press coverage and other media speculation, as well as corporate and government reports. People recognized that long-working systems could break down when the "...97, 98, 99..." ascending numbering assumption suddenly became invalid. Companies and organizations world-wide checked and upgraded their computer systems.

While no significant computer failures occurred with global significance when the clocks rolled over into 2000, preparation for the Y2K bug had a significant effect on the computer industry. The fact that countries where very little was spent on tackling the Y2K bug (such as Italy and South Korea) fared just as well as those who spent much more (such as the United Kingdom and the United States) has generated debate on whether the absence of computer failures was the result of the preparation undertaken or whether the significance of the problem had been overstated

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.

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.^[2]

The acronym Y2K has been attributed to David Eddy, a Massachusetts programmer,^[3] in an e-mail sent on June 12, 1995. He later said, "People were calling it CDC (Century Date Change) and FADL (Faulty Date Logic). There were other contenders. It just came off my COBOL calloused fingertips."^{[citation needed]}

It was speculated that 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 be interpreted by software as the year 1900. This would cause date comparisons to produce incorrect results. It was also thought that embedded systems, making use of similar date logic, might fail and cause utilities and other crucial infrastructure to fail.

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The Y2K problem is the electronic equivalent of the El Niño and there will be nasty surprises around the globe. – John Hamre, Deputy Secretary of Defense [4]

”

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. It was only the safe passing of the main "event horizon" itself, January 1, 2000, that fully quelled public fears.

In North America the actions taken to remedy the possible problems had unexpected benefits. Many businesses installed computer backup systems for critical files. The Y2K preparations had an impact on August 14, 2003 during the Northeast Blackout of 2003. The previous activities had included the installation of new electrical generation equipment and systems, which allowed for a relatively rapid restoration of power in some areas.

The practice of using two-digit dates for convenience long predates computers, notably in artwork. Abbreviated dates do not pose a problem for humans, as works and events pertaining to one century are sufficiently different from those of other centuries. Computers, however, are unable to make such distinctions.

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I’m one of the culprits who created this problem. I used to write those programs back in the 1960s and 1970s, and was proud of the fact that I was able to squeeze a few elements of space out of my program by not having to put a 19 before the year. Back then, it was very important. We used to spend a lot of time running through various mathematical exercises before we started to write our programs so that they could be very clearly delimited with respect to space and the use of capacity. It never entered our minds that those programs would have lasted for more than a few years. As a consequence, they are very poorly documented. If I were to go back and look at some of the programs I wrote 30 years ago, I would have one terribly difficult time working my way through step-by-step. – Alan Greenspan[5]

”

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 two characters 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 the problem 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 ignored until the last few years of the decade.

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 defined origin. Rollover 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 (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, and will roll over (exceed 32 bits) in 2038 and cause the Year 2038 problem. To solve this problem, many systems and languages have switched to a 64-bit version, or supplied alternatives which are 64-bit.
• 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^[6]. 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 originally did have the problem that it returned only the year number within the 20th century, and for compatibility's sake still represents the year as year minus 1900. Many programmers in C, and in Perl and Java, two programming languages widely used in web development that use the C functions, incorrectly treated this value as the last two digits of the year. On the web this usually was a harmless bug, but it did cause many dynamically generated webpages to display January 1, 2000, as "1/1/19100", "1/1/100", or variations of that depending on the format.
• 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 3.1 file manager, dates were shown as 1/1/19:0 for 1/1/2000. An update was available.

Even before January 1, 2000 arrived, there were also some worries about September 9, 1999 (albeit lesser compared to those generated by Y2K). This date could also be written in the numeric format, 9/9/99. This date value was frequently used to specify an unknown date; it was thus possible that programs might act on the records containing unknown dates on that day.^[7] It is also somewhat similar to the end-of-file code, 9999, in old programming languages. It was feared that some programs might unexpectedly terminate on that date. The bug, however, was more likely to confuse computer operators than machines.

Another potential problem for calculations involving 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 but not divisible by 100 unless also divisible by 400. For example, 1600 was a leap year, but 1700, 1800 and 1900 were not. Fortunately, most programs were able to rely on the oversimplified rule that a year divisible by 4 is a leap year. This method works fine for the year 2000, and will not become a problem until 2100, when hopefully these older legacy programs will have long since been replaced.

The problem was compounded by the need of many systems, especially in the financial services sector, to calculate expiration and renewal dates in the future. For example, a company tracking five-year bonds would experience Y2K problems in 1995, when its systems needed to calculate an expiration date of 2000, which with two-digit years, its "00" expiration year would seem to be earlier than the "95" of the issue date.

Millennium

A millennium (pl. millennia) is a period of time equal to one thousand years (from Latin mille, thousand, and annum, year). The term may implicitly refer to calendar millennia; periods tied numerically to a particular dating system, specifically ones that begin at the starting (initial reference) point of the calendar in question (typically the year 1) or in later years which are whole number multiples of a thousand years after it.

The term can also refer to an interval of time beginning on any date. Frequently in the latter case (and sometimes also in the former) it may have religious or theological implications (see Millenarianism). Especially in religious usage such an interval may be interpreted less precisely, not being, exactly, 1,000 years long.

Ordinal

The original method of counting years was ordinal, whether 1st year A.D. or regnal 10th year of King Henry VIII. This ordinal numbering is still present in the names of the millennia and centuries, for example 1st Millennium or the 20th century, and sometimes in the names of decades, e.g. 1st decade of the 21st century.

[edit] Cardinal

In recent years, most people have moved to expressing individual years as cardinal numbers, for example 1945 or 1998. The usage 1999th year A.D. is no longer found. This follows scientific usage, for example astronomical year numbering. As a result, some other calendar names have also moved to cardinals, e.g. 1980s is an acceptable name for a particular decade. However, 1600s could be understood as either a decade or a century.

[edit] Ranges

A change from ordinals to cardinals is incomplete and might not ever be completed; the main issues arise from the content of the various year ranges. Similar issues affect the contents of decades and centuries.

Those following ordinal year names naturally choose

• 2001–2010 as the current decade
• 2001–2100 as the current century
• 2001–3000 as the current millennium

Those following cardinal year names equally naturally choose

• 2000–2009 as the current decade
• 2000–2099 as the current century
• 2000–2999 as the current millennium

[edit] Debate over millennium celebrations

The common Western calendar, i.e. the Gregorian calendar, has been defined with counting origin 1. Thus each period of 1,000 years concludes with a year number with three zeroes, e.g. the first thousand years in the Western calendar included the year 1000. However, there are two viewpoints about how millennia should be thought of in practice, one which relies on the formal operation of the calendar and one which appeals to other notions that attract popular sentiment.

There was a popular debate leading up to the celebrations of the year 2000 as to whether the beginning of that year should be understood (and celebrated) as the beginning of a new millennium. Historically, there has been debate around the turn of previous decades, centuries, and millennia.

[edit] Arbitrarity

As a side-note to the debate on timing of the turn of the millennium, the arbitrariness of the era itself can be raised. The Gregorian calendar is a secularized, de facto standard, based on a significant Christian event, the purported date of Jesus' birth; thus the foundation of the calendar may not be as relevant to non-Christians. The calendar is one among many still in use and those used historically. Adjustments and errors in the calendar (such as Dionysius Exiguus's incorrect calculation of A.D. 1) make the particular dates we use today arbitrary.

However, given that the Gregorian calendar is a widely used standard, it is valid to discuss the significant dates within it, be it the timing of religious festivals (such as the moving date of Easter which Dionysius Exiguus was involved in calculating) or the delineation of significant periods of time, such as the end of a millennium.

[edit] Viewpoint 1: x001–y000

Those holding that the arrival of new millennium should be celebrated in the transition from 2000 to 2001 (i.e. December 31, 2000), argued that since the Gregorian Calendar has no year zero, the millennia should be counted from A.D. 1. Thus the first period of one thousand complete years runs from the beginning of A.D. 1 to the end of A.D. 1000, and the beginning of the second millennium took place at the beginning of 1001. The second millennium thus ends at the end of the year 2000. Then again, those who defend the opposite idea state that the new millennium started with the year 2000 (because of the changes made to the Gregorian calendar in 1582, or because the first millennium started in 1 A.D. and ended in 999 A.D., being the only millennium (along with the last millennium b.c.) not with 1000 years, but with 999 years).

Illustration of years with a 00-01 demarcation

2 BC	1 BC	AD 1	AD 2	3	4	5	...	998	999	1000	1001	1002	...	1998	1999	2000	2001	2002	...	2998	2999	3000	3001	3002
		First one thousand years (millennium)									Second millennium						Third millennium

Arthur C. Clarke gave this analogy (from a statement received by Reuters): "If the scale on your grocer's weighing machine began at 1 instead of 0, would you be happy when he claimed he'd sold you 10 kg of tea?" This statement illustrates the common confusion about the calendar.

If one counts from the beginning of A.D. 1 to the ending of A.D. 1000, one would have counted 1000 years. The next 1000 years (millennium) would begin on the first day of 1001. So the calendar has not 'cheated' anyone out of a year.

In other words, the argument is based on the fact that the last year of the first two thousand years in the Gregorian Calendar was 2000, not 1999.

[edit] Popular culture: x000–x999

The "year 2000" has also been a popular phrase referring to an often utopian future, or a year when stories in such a future were set, adding to its cultural significance. There was also media and public interest in the Y2K bug. Thus, the populist argument was that the new millennium should begin when the zeroes of 2000 "rolled over," i.e. December 31, 1999. People felt that the change of hundred digit in the year number, and the zeros rolling over, created a sense that a new century had begun. This is similar to the common demarcation of decades by their most significant digits, e.g. naming the period 1980 to 1989 as the 1980s or "the eighties." Similarly, it would be valid to celebrate the year 2000 as a cultural event in its own right, and name the period 2000 to 2999 as "the 2000s."

Most historians agree that Dionysius nominated Christ's birth as 25th December of the year before AD 1 (ref History Today June 1999 p60 Letters, Darian Hiles: "Of Dates and Decimals"). This corresponded with the belief that the birth year itself was considered too holy to mention^{[citation needed]}. It also corresponds to the notion that AD 1 was "the first year of his life," as distinguished from being the year after his first birthday.

Similarly in AD 1000 the church actively discouraged any mention of that year and in modern times it labelled AD 2000 as the "Jubilee Year 2000" marking the 2000th anniversary of the birth of Christ. The AD system counts years with origin 1. Some assume a preceding Year 0 for the start of the first Christian millennium in order to start the millennia in year numbers multiple of 1000. This results in such first millennium containing only 999 Gregorian years.

Illustration of years with a 99-00 demarcation using Year zero (ISO 8601 and astronomical numbering system)

−1 AD	0	1	2	3	4	5	...	998	999	1000	1001	1002	...	1998	1999	2000	2001	2002	...	2998	2999	3000	3001	3002
	First millennium (1000 years)									Second millennium						Third millennium

Illustration of years with a 99-00 demarcation (starting AD 1)

1 BC	1 AD	2	3	4	5	...	998	999	1000	1001	1002	...	1998	1999	2000	2001	2002	...	2998	2999	3000	3001	3002
	First millennium (999 years only)								Second millennium						Third millennium

[edit] Popular approach

The majority popular approach was to treat the end of 1999 as the end of a millennium, and to hold millennium celebrations at midnight between December 31, 1999 and January 1, 2000, as per viewpoint 2. The cultural and psychological significance of the events listed above combined to cause celebrations to be observed one year earlier than the formal Gregorian date. This does not, of course, establish that insistence on the formal Gregorian date is "incorrect", though some view it as pedantic (as in the comment of Douglas Adams mentioned below).

Some event organisers hedged their bets by calling their 1999 celebrations things like "Click" referring to the odometer-like rolling over of the nines to zeros.