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Definition: macOS

The name of Apple's Unix-based operating system for Mac desktop and laptop computers. macOS is a continuation of the Mac OS X operating system, which was rebranded as macOS starting with the Sierra version in 2016.

Since its introduction in 1984, the Mac operating system has had five brand names (see below) and was designed to work with four hardware lines: Motorola, PowerPC, Intel and ARM. See Motorola, PowerPC, Intel Mac, Apple M1, macOS server and Mac computer.

Name Evolution
The Mac originally used "System" designations for its operating system, which then became "Mac OS." Starting in 1999, Mac OS X was a major upgrade that was branded with animal names followed by places in California (see Mac OS X).

  Intro.  Name       Versions

  2020   "macOS"     11.0   Big Sur
  2019   "macOS"     10.15  Catalina
  2018   "macOS"     10.14  Mojave
  2017   "macOS"     10.13  High Sierra
  2016   "macOS"     10.12  Sierra

  2013   "OS X"      10.9 to 10.11

  1999   "Mac OS X"  10.0 to 10.8

  1995   "Mac OS"    7.6 to 9.2

  1984   "System"    1 to 7.5

Long Live the Mac Operating System
Introduced in 1999, Mac OS 8.6 was the first time the version number appeared on the Mac startup screen. Two years earlier, Mac OS 8.0 was the largest update to the Mac operating system since System 7.