Y2K was the abbreviated name of the Millennium Bug. Short for "Year 2000", Y2K refers to a bit-saving technique used in antiquated computer systems in which two digits were used to represent years, instead of the usual four digits. Thus, for example, the year "1984" would be represented as simply "84". Many such systems only supported dates from 1900 to 1999, with the year 1999 rolling back to 1900 after December 31, 1999. Although most computer systems in use at the turn of the century had been designed to support dates later than December 31, 1999, certain legacy systems that had not been expected to last into the new millennium at the time of their creation were at risk of serious fault should they have encountered the new dates. Of particular interest were banking, government, and other financial systems, many of which perform calculations based upon date. Having the systems perform date arithmetic with a 100 year discrepancy in the actual data would have created unusual, and in some cases even catastrophic, incidents.
In the 1960s and 1970s the computer industry saw very rapid development, and many hardware and software innovations were outdated and replaced within 5 years of their introduction. At the time processor power, RAM memory, and disk space were very expensive, thus shortcuts to reduce their use were taken wherever possible. As counting above the number 1024 would require at least 11 bits, but counting up to the number 128 requires only a 7 bits, most computer systems only stored the last two digits of dates in data that was certain to be from the then-current century. The correct date was rendered by simply adding 1900 to the stored date. As these systems were expected to be replaced long before the year 2000, the system was logical at the time of it's inception. However, many governments and financial institutions adopted these computer systems. As these institutions are typically slow to change, especially compared to the computer and other high-tech industries, they kept these Y2K-liable machines operating long after their designers had expected. Only in the last few years, and in some cases even weeks, before the turn of the millennium did these bodies take action to correct possible Y2K faults.
Worldwide, between 250 billion and 325 billion US Dollars were spent in preparation for Y2K. Very few date-related problems were publicly reported in January 2000, however, expert opinion is divided as to whether this was due to proper preparation, non-disclosure, or simple over-exaggeration of the consequences. Nevertheless, due to the heavy press coverage and mainstream acceptance of the term, the designation "Y2K" is now used to refer to any date that will be problematic for computers for any technical reason. For instance, the term Y2K is often used retroactively in reference to the date September 9, 1999. The date 9-9-99 was often used in the 1960s and 1970s as an expiration date for archived data, with the expectation that the systems in question would be replaced long before the actual date arrived. Other years with technically problematic renderings include 2038, 2070, and 10,000.
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