Master/slave (technology)

Master/slave is the historical terminology for a model of asymmetric communication or control where one device or process (the "master") controls one or more other devices or processes (the "slaves") and serves as their communication hub. In some systems, a master is selected from a group of eligible devices, with the other devices acting in the role of slaves. The master/slave terminology was first used in 1904. Since the early 21st century, the terms have become a subject of controversy from their association with slavery and some organizations have opted to replace them with alternative terms. In electronics, master/slave relationships are used to describe some of the following scenarios: In parallel ATA hard drive arrangements, the terms master and slave are used to describe drives on the same cable, but neither drive has control or priority over the other. A master clock that provides time signals used to synchronize one or more slave clocks as part of a clock network. In AXI, master and slave have differing roles, with master initiating transactions and the slave responding to those transactions. A Serial Peripheral Interface bus typically has a single master controlling multiple slaves. Many people recommend using more modern terms (main/sub, controller/peripheral, etc.) and discontinuing the use of master/slave terms. Edge-triggered flip-flops can be created by arranging two latches (master latch and slave latch) in a master/slave configuration. It is named because the master latch controls the slave latch's value and forces the slave latch to hold its value, as the slave latch always copies its new value from the master latch. In database replication, the master database is regarded as the authoritative source, and the slave (also called replica) databases are synchronized to it. In photography, secondary or slave flash units may be synchronized to the master unit to provide light from additional directions. Duplication is often done with several cassette tapes or compact disc recorders linked together.