(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
2025 26.0 Tahoe
2024 15.0 Sequoia
2023 14.0 Sonoma
2021 13.0 Ventura
2021 12.0 Monterey
2020 11.0 Big Sur
2019 10.15 Catalina
2018 10.14 Mojave
2017 10.13 High Sierra
2016 10.12 Sierra
OS X Version Place
2015 10.11 El Capitan
2014 10.10 Yosemite
2013 10.9 Mavericks
OS X Version Jungle Cat
2012 10.8 Mountain Lion
2011 10.7 Lion
2009 10.6 Snow Leopard
2007 10.5 Leopard
2005 10.4 Tiger
2003 10.3 Panther
2002 10.2 Jaguar
2001 10.1 Puma (code name)
2001 10.0 Cheetah (code name)