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Flag day (computing)
View on WikipediaA flag day, as used in system administration, is a change which requires a complete restart or conversion of a sizable body of software or data. The change is large and expensive, and—in the event of failure—similarly difficult and expensive to reverse.[1]
The situation may arise if there are limitations on backward compatibility and forward compatibility among system components, which then requires that updates be performed almost simultaneously (during a "flag day cutover") for the system to function after the upgrade. This contrasts with the method of gradually phased-in upgrades, which avoids the disruption of service caused by en masse upgrades.
This systems terminology originates from a major change in the Multics operating system's definition of ASCII, which was scheduled for the United States holiday, Flag Day, on June 14, 1966.[1][2][3]
Another historical flag day was January 1, 1983, when the ARPANET changed from NCP to the TCP/IP protocol suite. This major change required all ARPANET nodes and interfaces to be shut down and restarted across the entire network.[4]
See also
[edit]References
[edit]- ^ a b "flag day". Retrieved 2008-09-22.
- ^ Eric S. Raymond (1996). The New Hacker's Dictionary. MIT Press. pp. 192–. ISBN 978-0-262-68092-9.
- ^ "Multicians Glossary: F". Retrieved 2025-07-18.
- ^ Jon Postel (November 1981). NCP/TCP Transition Plan. doi:10.17487/RFC0801. RFC 801.
