macOS (previously OS X and originally Mac OS X) is an operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and laptop computers, it is the second most widely used desktop OS, after Microsoft Windows and ahead of Linux (including ChromeOS).
macOS succeeded the classic Mac OS, a Macintosh operating system from 1984 to 2001. During this time, Apple co-founder Steve Jobs had left Apple and started another company, NeXT, developing the NeXTSTEP platform that would later be acquired by Apple to form the basis of macOS.
The first desktop version, Mac OS X 10.0, was released on March 24, 2001. Mac OS X 10.5 Leopard, Mac OS X 10.6 Snow Leopard and all releases from OS X 10.8 Mountain Lion to macOS 14 Sonoma are UNIX 03 certified. The derivatives of macOS are Apple's other operating systems: iOS, iPadOS, watchOS, tvOS, and audioOS.
A 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. 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. 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.
macOS has supported three major processor architectures, beginning with PowerPC-based Macs in 1999. In 2006, Apple transitioned to the Intel architecture with a line of Macs using Intel Core processors. In 2020, Apple began the Apple silicon transition, using self-designed, 64-bit ARM-based Apple M series processors on the latest Macintosh computers. As of 2023, the most recent release of macOS is macOS 14 Sonoma.
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