Master-slave (technology)

Master/slave is a model of communication where one device or process has unidirectional control over one or more other devices. In some systems a master is selected from a group of eligible devices, with the other devices acting in the role of slaves.

In other words, "The master/slave configuration is basically used for load sharing purposes when two identical motors connected to two different drives are coupled to a common load". One drive is defined as the master and is configured for running in the speed-control mode whereas the other defined as slave is configured for running in torque-control mode.

In 2003, the County of Los Angeles in California asked that manufacturers, suppliers and contractors to stop using "master" and "slave" terminology on its products; the county made this request "based on the cultural diversity and sensitivity of Los Angeles County". Following outcries about the request, the County of Los Angeles issued a statement saying that the decision was "nothing more than a request". Due to the controversy, the term was selected as the most politically incorrect word in 2004 by Global Language Monitor.

In May 2014, GitHub user fcurella submitted a pull request to the GitHub repository for the Python framework Django, initially changing it to "leader/follower" and finally to "primary/replica". This triggered an active discussion of the appropriateness of the master/slave terminology as well as the appropriateness of the change.

In June 2014, Drupal 8 did the same as Django did, citing that the word "replica" is already in use by IBM, Microsoft, Engine Yard, Amazon Web Services, and ACM.

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