A flag day, as used in

system administration A system administrator, or sysadmin, or admin is a person who is responsible for the upkeep, configuration, and reliable operation of computer systems, especially multi-user computers, such as servers. The system administrator seeks to ensu ...

, 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. 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. Another historical flag day was January 1, 1983, when the ARPANET changed from

NCP NCP may refer to: Science and medicine * Novel Coronavirus Pneumonia (a temporary name for COVID-19), an outbreak that was officially identified in late 2019. * HIV-1 nucleocapsid protein 7 (NCp7), a target of zinc finger inhibitors * Nucleosome ...

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.

Jon Postel Jonathan Bruce Postel (; August 6, 1943 – October 16, 1998) was an American computer scientist who made many significant contributions to the development of the Internet, particularly with respect to standards. He is known principally for be ...

NCP/TCP Transition Plan, RFC 801
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References

Computer jargon {{compsci-stub

See also

References