flag = F = flaky

flag day n.

A software change that is neither forward- nor backward-compatible, and which is costly to make and costly to reverse. "Can we install that without causing a flag day for all users?" This term has nothing to do with the use of the word flag to mean a variable that has two values. It came into use when a massive change was made to the CTSS timesharing system to convert from the short-lived 1965 version of the ASCII code to the 1967 version (in draft at the time); this was scheduled for Flag Day (a U.S. holiday), June 14, 1966. The actual change moved the code point for the ASCII newline character; this required that all of the CTSS source code, documentation, and device drivers be changed simultaneously. See also backward combatability. [Previous versions of this entry described this as a change in Multics, which was wrong. Evidently this confusion arose from the fact that the changes were made partly to facilitate Multics development --ESR] [As it happens, the first commercial installation of a computer, a Univac I, took place on Flag Day of 1951 --ESR]

--The Jargon File version 4.3.1, ed. ESR, this entry manually entered by rootbeer277.

Flag day is a very minor American holiday held on June 14. On this day residents may sometimes be urged to fly the American flag, and some very few communities may hold parades.

While previously various states had celebrated flag day, it wasn't until 1916 that President Woodrow Wilson declared that flag day would be celebrated nation-wide. This was later made even more official by congress, but not made a federal holiday.

Flag day officially commemorates the adoption of the first stars and stripes flag of the United States by the Second Continental Congress on June 14, 1777. Prior to this they had continued to use a modified Union Flag, called the Grand Union Flag.

Most Americans do not really register that flag day exists, as it is fully overshadowed in the popular mind by the official day of unbounded patriotism, Independence Day (commonly referred to as the Fourth of July).

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