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macOSThe name of Apple's Mac operating system, starting with the Sierra Version 10.12 in 2016. Sierra is officially "macOS Sierra" rather than Mac OS X Sierra. Since its introduction in 1984, Mac operating systems have been written for three hardware lines: Motorola, PowerPC and Intel. See Macintosh and operating system.
The Mac originally used System 1 through System 7 designations for its operating systems until 1997, when Version 8 became Mac OS 8. OS 8 was superseded by Mac OS 9 in 1999, which was followed by Mac OS 10 (Mac OS X) in 1999 and 2001 for server and desktop versions respectively. The Mac OS X moniker was maintained throughout subsequent versions with each new release given an animal name, such as Tiger and Leopard, and starting with Mac OS X 10.9, a location in California, such as Mavericks and Yosemite. Starting with Sierra, the base name of the product changed from Mac OS X to macOS. See Mac OS X and Sierra.