MacOS retained the major version number 10 throughout its development history until the release of macOS 11 Big Sur in 2020 releases of macOS have also been named after big cats (versions 10.0–10.8) or locations in California (10.9–present). The operating system was further renamed to 'macOS' starting with macOS Sierra. 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.

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. The macOS Server app has been discontinued since April 2022 and will no longer work on macOS versions past macOS 12 Monterey.

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. Since then, several more distinct desktop and server editions of macOS have been released. The desktop version aimed at regular users- Mac OS X 10.0-shipped in March 2001. It was built using the technologies Apple acquired from NeXT, but didn’t include the signature Aqua user interface (UI). MacOS was first released in 1999 as Mac OS X Server 1.0. To ease the transition for users and developers, versions through 10.4 were able to run Mac OS 9 and its applications in a compatibility layer. The transition was a technologically and strategically significant one. 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.Īlthough it was originally marketed as simply 'version 10' of the 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. 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. 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.

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