The year 1900 problem concerns the misinterpretation of years recorded by only their last two digits, and whether they occurred before or after the year 1900. Unlike the
year 2000 problem
The term year 2000 problem, or simply Y2K, refers to potential computer errors related to the Time formatting and storage bugs, formatting and storage of calendar data for dates in and after the year 2000. Many Computer program, programs repr ...
, it is not tied to
computer software
Software consists of computer programs that instruct the Execution (computing), execution of a computer. Software also includes design documents and specifications.
The history of software is closely tied to the development of digital comput ...
alone, since the problem existed before
electronic computers did and has also cropped up in manual systems.
The most common issue raised by the year 1900 problem regards people's ages. Often, a person's birth year was registered with only two digits, on the assumption that either it was not important exactly how old a person is, or that no one lives longer than one hundred years. In several countries, especially in Europe, a
national identification number
A national identification number or national identity number is used by the governments of many countries as a means of uniquely identifying their citizens or residents for the purposes of work, taxation, government benefits, health care, bank ...
was introduced (often in the 1950s), including two-digit information about the birth year.
The largest unwelcome side effect from this is people 100 or more years old being mistaken for young children or in some cases, young children being mistaken for adults.
When handling the year 2000 problem, measures were sometimes taken to avoid or rectify this: modifying the national identification number, for instance. For example, year is recorded only with two digits in Bulgarian
Uniform civil number; however, a solution was ready as early as the inception of the system in 1975: 20 was added to the month number for an individual born before 1900 and 40 for those born in or after 2000.
Microsoft Excel
Microsoft Excel
Microsoft Excel is a spreadsheet editor developed by Microsoft for Microsoft Windows, Windows, macOS, Android (operating system), Android, iOS and iPadOS. It features calculation or computation capabilities, graphing tools, pivot tables, and a ...
(using the default 1900 Date System) cannot display dates before the year 1900, although this is not due to a two-digit integer being used to represent the year: Excel uses a
floating-point
In computing, floating-point arithmetic (FP) is arithmetic on subsets of real numbers formed by a ''significand'' (a Sign (mathematics), signed sequence of a fixed number of digits in some Radix, base) multiplied by an integer power of that ba ...
number to store dates and times. The number 1.0 represents the first second of January 1, 1900, in the 1900 Date System (or January 2, 1904, in the 1904 Date System – the default for Macintosh prior to Excel 2016). Numbers smaller than this display as a
#VALUE! error.
[How to Work With Dates Before 1900 in Excel](_blank)
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For compatibility with Lotus 1-2-3
Lotus 1-2-3 is a discontinued spreadsheet program from Lotus Software (later part of IBM). It was the first killer application of the IBM PC, was hugely popular in the 1980s, and significantly contributed to the success of IBM PC-compatibles ...
, the 1900 Date System incorrectly accepts the date February 29, 1900, even though 1900 was not a leap year. This also has the side effect that the WEEKDAY function reports incorrect values for the period Jan 01 1900 to Feb 28 1900.
See also
* Time formatting and storage bugs
In computer science, data type limitations and software bugs can cause errors in system time, time and date calculation or display. These are most commonly manifestations of arithmetic overflow, but can also be the result of other issues. The bes ...
* System time
In computer science and computer programming, system time represents a computer system's notion of the passage of time. In this sense, ''time'' also includes the passing of calendar date, days on the calendar.
System time is measured by a ''sys ...
* Perpetual calendar
References
{{Year-related problems
Problem
Problem solving is the process of achieving a goal by overcoming obstacles, a frequent part of most activities. Problems in need of solutions range from simple personal tasks (e.g. how to turn on an appliance) to complex issues in business an ...
Year 01900 Problem