Flag day (software)

From Wikipedia, the free encyclopedia
Jump to: navigation, search

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 it doesn't work—reversing the change is similarly difficult and expensive.[1]

This usage originates from a change in the Multics operating system's definition of ASCII, which was scheduled for the U.S. holiday, Flag Day, on June 14, 1966.[1][2]

Another flag day was January 1, 1983, when the ARPANET changed from NCP to the TCP/IP protocol suite.[3]


  1. ^ a b "flag day". Retrieved 2008-09-22. 
  2. ^ Eric S. Raymond (1996). The New Hacker's Dictionary. MIT Press. pp. 192–. ISBN 978-0-262-68092-9. 
  3. ^ Jon Postel, NCP/TCP Transition Plan, RFC 801