Its graphical user interface was built on top of an object-oriented GUI toolkit using the Objective-C programming language. The kernel of NeXTSTEP is based upon the Mach kernel, which was originally developed at Carnegie Mellon University, with additional kernel layers and low-level user space code derived from parts of BSD. There, the Unix-like NeXTSTEP operating system was developed, before being launched in 1989. The heritage of what would become macOS had originated at NeXT, a company founded by Steve Jobs following his departure from Apple in 1985. As of 2023, the most recent release of macOS is macOS 14 Sonoma. In 2020, Apple began the Apple silicon transition, using self-designed, 64-bit ARM-based Apple M series processors on the latest Macintosh computers. In 2006, Apple transitioned to the Intel architecture with a line of Macs using Intel Core processors.

MacOS has supported three major processor architectures, beginning with PowerPC-based Macs in 1999. After sixteen distinct versions of macOS 10, macOS Big Sur was presented as version 11 in 2020, and every subsequent version has also incremented the major version number, similarly to classic Mac OS and iOS. Apple shortened the name to 'OS X' in 2011 and then changed it to 'macOS' in 2016 to align with the branding of Apple's other operating systems, iOS, watchOS, and tvOS.

The derivatives of macOS are Apple's other operating systems: iOS, iPadOS, watchOS, tvOS, and audioOS.Ī prominent part of macOS's original brand identity was the use of Roman numeral X, pronounced 'ten', as well as code naming each release after species of big cats, or places within California. All releases from Mac OS X Leopard onward (except for OS X Lion) are UNIX 03 certified. The first desktop version, Mac OS X 10.0, was released on March 24, 2001. Its underlying architecture came from NeXT's NeXTSTEP, as a result of Apple's acquisition of NeXT, which also brought Steve Jobs back to Apple. Mac OS X succeeded classic Mac OS, a Macintosh operating system from 1984 to 2001. Within the market of desktop and laptop computers, it is the second most widely used desktop OS, after Microsoft Windows and ahead of all Linux distributions, including ChromeOS. It is the primary operating system for Apple's Mac computers. MacOS ( / ˌ m æ k oʊ ˈ ɛ s/ ), originally Mac OS X, previously shortened as OS X, is an operating system developed and marketed by Apple Inc.

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