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Definition: Mac OS X


(Mac OS 10) The operating system from Apple for the Mac family from 2001 until the fall of 2016, at which time the Sierra OS Version 10.12 began using the rebranded "macOS" moniker. As a result, all the names of Apple operating systems have the same OS suffix (macOS, iOS, iPadOS, tvOS). See macOS and Sierra.

OS X Server was introduced in 1999, and the client version came out in 2001. Based on Unix and featuring an entirely redesigned user interface, OS X was a major departure from the previous OS 9 system. For the first time, the rich set of Unix commands became available to all Mac developers (A/UX was an earlier Unix OS for the Mac but was not widely used).

OS X added protected memory, pre-emptive multitasking, multithreading and symmetric multiprocessing (SMP) to the Mac world. The heart of OS X is the open source, POSIX-compliant Darwin kernel, which includes an enhanced BSD 4.4 operating system and Mach 2.5 microkernel. See HFS.

Legacy Software
Prior to Mac OS X 10.5 (Leopard), OS X ran legacy OS 9 and earlier applications via its Classic software, which was a full copy of OS 9 that ran as an OS X process. Classic was not preloaded on new Macs, but was available for installation from the system disks.

In 2006, Apple switched from the PowerPC to the Intel platform, and Classic support was dropped in the Intel version of OS X. However, PowerPC applications could run on Intel Macs via an emulator (see Rosetta).

Programming Environments
There have been five programming interfaces (APIs) for writing Mac OS X applications. Cocoa is the native OS X interface, derived from OpenStep. Carbon is used for applications that can run on both OS X and earlier Mac OS machines, and Classic is the API prior to Mac OS X. Programs can also be developed in Java and BSD. See OpenStep and Cocoa.

Faster Cats!
Mac OS X versions were internally code-named after jungle cats. Starting with Version 10.2 (Jaguar), the animals became part of the official product name until Version 10.9 when places in California were used instead (see below). See Rhapsody and Bonjour.

  macOS Version  Place
  13.0   2021    Ventura
  12.0   2021    Monterey
  11.0   2020    Big Sur
  10.15  2019    Catalina
  10.14  2018    Mojave
  10.13  2017    High Sierra
  10.12  2016    Sierra

  OS X Version   Place
  10.11  2015    El Capitan
  10.10  2014    Yosemite
  10.9   2013    Mavericks

  OS X Version   Jungle Cat
  10.8   2012    Mountain Lion
  10.7   2011    Lion
  10.6   2009    Snow Leopard
  10.5   2007    Leopard
  10.4   2005    Tiger
  10.3   2003    Panther
  10.2   2002    Jaguar
  10.1   2001    Puma (code name)
  10.0   2001    Cheetah (code name)