MacOS version history

The history of macOS, Apple's current Mac operating system formerly named Mac OS X until 2011 and then OS X until 2016, began with the company's project to replace its "classic" Mac OS. That system, up to and including its final release Mac OS 9, was a direct descendant of the operating system Apple had used in its Mac computers since their introduction in 1984. However, the current macOS is a UNIX operating system built on technology that had been developed at NeXT from the 1980s until Apple purchased the company in early 1997.^[1]

macOS components derived from BSD include multiuser access, TCP/IP networking, and memory protection.^[2]

Although it was originally marketed as simply "version 10" of Mac OS (indicated by the Roman numeral "X"), it has a completely different codebase from Mac OS 9, as well as substantial changes to its user interface. The transition was a technologically and strategically significant one. To ease the transition for users and developers, versions 10.0 through 10.4 were able to run Mac OS 9 and its applications in the Classic Environment, a compatibility layer.

macOS was first released in 1999 as Mac OS X Server 1.0. It was built using the technologies Apple acquired from NeXT, but did not include the signature Aqua user interface (UI). The desktop version aimed at regular users—Mac OS X 10.0—shipped in March 2001. Since then, several more distinct desktop and server editions of macOS have been released. Starting with Mac OS X 10.7 Lion, macOS Server is no longer offered as a standalone operating system; instead, server management tools are available for purchase as an add-on. The macOS Server app was discontinued on April 21, 2022 and will stop working on macOS 13 Ventura or later. Starting with the Intel build of Mac OS X 10.5 Leopard, most releases have been certified as Unix systems conforming to the Single UNIX Specification.^{[3][4][5][6][7]}

Lion was referred to by Apple as "Mac OS X Lion" and sometimes as "OS X Lion"; Mountain Lion was officially referred to as just "OS X Mountain Lion", with the "Mac" being completely dropped. The operating system was further renamed to "macOS" starting with macOS Sierra.

From the introduction of machines not supporting the classic Mac OS in 2003 until the introduction of iPhone OS in early 2007, Mac OS X was Apple's only software platform.

macOS retained the major version number 10 throughout its development history until the release of macOS 11 Big Sur in 2020.

Mac OS X 10.0 and 10.1 were given names of big cats as internal code names ("Cheetah" and "Puma"). Starting with Mac OS X 10.2 Jaguar, big-cat names were used as marketing names; starting with OS X 10.9 Mavericks, names of locations in California were used as marketing names instead.

The current major version, macOS 15 Sequoia, was announced on June 10, 2024 at WWDC 2024 and released on September 16 of that year.