macOS (originally Mac OS X, previously shortened as OS X) is an operating system developed and marketed by Apple 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 all Linux distributions, including ChromeOS. Mac OS X succeeded classic Mac OS, the primary Macintosh operating system from 1984 to 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. The first desktop version, Mac OS X 10.0, was released on March 24, 2001. All releases from Mac OS X Leopard onward (except for OS X Lion) are UNIX 03 certified.[9][10] 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, and later, 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.[12] 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. 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.