MacOS
macOS is a proprietary Unix-based operating system, derived from OPENSTEP for Mach and FreeBSD, which has been marketed and developed by Apple since 2001. It is the current operating system for Apple's Mac computers. Within the market of desktop and laptop computers, it is currently the second most widely used desktop OS, after Microsoft Windows and ahead of all Linux distributions, including ChromeOS and SteamOS., the most recent release of macOS is macOS 26 Tahoe, the 22nd major version of macOS.
Mac OS X succeeded the 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. Mac OS X Leopard and all later versions of macOS, other than OS X Lion, are UNIX 03 certified. Each of Apple's other contemporary operating systems, including iOS, iPadOS, watchOS, tvOS, audioOS and visionOS, are derivatives of macOS. Throughout its history, macOS has supported three major processor architectures: the initial version supported PowerPC-based Macs only, with support for Intel-based Macs beginning with OS X Tiger 10.4.4 and support for ARM-based Apple silicon Macs beginning with macOS Big Sur. Support for PowerPC-based Macs was dropped with OS X Snow Leopard, and it was announced at the 2025 Worldwide Developers Conference that macOS Tahoe will be the last to support Intel-based Macs.
A prominent part of macOS's original brand identity was the use of the 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. In 2020, macOS Big Sur was presented as version 11—a marked departure after 16 releases of macOS 10—but the naming convention continued to reference places within California. In 2025, Apple unified the version number across all of its products to align with the year after their WWDC announcement, so the release announced at the 2025 WWDC, macOS Tahoe, is macOS 26.
History
Development
The heritage of what would become macOS originated at NeXT, a company founded by Steve Jobs following his departure from Apple in 1985. There, the Unix-like NeXTSTEP operating system was developed, before being launched in 1989. 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 FreeBSD and other BSD operating systems. Its graphical user interface was built on top of an object-oriented GUI toolkit using the programming language.Throughout the 1990s, Apple had tried to create a "next-generation" OS to succeed its classic Mac OS through the Taligent, Copland and Gershwin projects; however, all were eventually abandoned. This led Apple to acquire NeXT in 1997, allowing NeXTSTEP, later called OPENSTEP, to serve as the basis for Apple's next-generation operating system.
The acquisition also led to Steve Jobs returning to Apple as interim and later permanent CEO, shepherding the transformation of the programmer-friendly OPENSTEP into a system that would be adopted by Apple's primary market of home users and creative professionals. The project was codenamed "Rhapsody" before being officially named Mac OS X.
Mac OS X
The "X" in Mac OS X's name represents the Roman numeral for the number ten, and Apple has stated that it should be pronounced "ten" in this context; it is also commonly pronounced like the letter "X". The iPhone X, iPhone XR and iPhone XS all later followed this convention.Previous Macintosh operating systems were named using Arabic numerals, as with Mac OS 8 and Mac OS 9. Until version 11, macOS Big Sur, all versions of the operating system were given version numbers of the form 10.x, with this format persisting from Mac OS X 10.0 through 10.15; starting with macOS Big Sur, Apple switched to integer version numbers that increased by 1 with every major release.
The first version of Mac OS X, Mac OS X Server 1.0, was a transitional product, featuring an interface resembling the classic Mac OS, though it was not compatible with software designed for the older system; consumer releases of Mac OS X included more backward compatibility. Mac OS applications could be rewritten to run natively via the Carbon API, with many alternatively able to be run directly through the Classic Environment albeit with a reduction in performance.
The consumer version of Mac OS X was launched in March 2001 with Mac OS X 10.0. Reviews were variable, with many praising its sophisticated, glossy Aqua interface, but criticizing it for sluggish performance. With Apple's popularity at a low, the developer of FrameMaker, Adobe Inc., declined to develop new versions of it for Mac OS X. Ars Technica columnist John Siracusa, who reviewed every major OS X release up to 10.10, described the early releases in retrospect as "dog-slow, feature poor" and Aqua as "unbearably slow and a huge resource hog".
Apple rapidly developed several new releases of Mac OS X. Apple released Mac OS X 10.1 in October 2001, delivering quality of life enhancements. Beginning in January 2002, Apple preinstalled Mac OS X as the default operating system on all Macs. Later that year Apple released Mac OS X Jaguar, the first version to publicly use its code name in marketing and advertisements. When Mac OS X Panther released in 2003, Siracusa noted that "It's strange to have gone from years of uncertainty and vaporware to a steady annual supply of major new operating system releases." Mac OS X Tiger, which released in 2005, reportedly shocked executives at Microsoft by offering a number of features, such as fast file searching and improved graphics processing, that Microsoft had spent several years struggling to add to Windows Vista with acceptable performance.
As the operating system evolved, it moved away from the classic Mac OS, with applications being added and removed. Considering music to be a key market, Apple developed the iPod music player and music software for the Mac, including iTunes and GarageBand. Targeting the consumer and media markets, Apple emphasized its new "digital lifestyle" applications such as the iLife suite, integrated home entertainment through the Front Row media center and the Safari web browser. With the increasing popularity of the internet, Apple offered additional online services, including the.Mac, MobileMe and most recently iCloud products. It later began selling third-party applications through the Mac App Store.
Newer versions of Mac OS X also included modifications to the general interface, moving away from the striped gloss and transparency of the initial versions. Some applications began to use a brushed metal appearance, or non-pinstriped title bar appearance in Mac OS X Tiger. In Mac OS X Leopard, Apple announced a unification of the interface, with a standardized gray-gradient window style.
In 2006, the first Intel Macs were released with a specialized version of Mac OS X Tiger.
A key development for the system was the announcement and release of the iPhone from 2007 onwards. While Apple's previous iPod media players used a minimal operating system, the iPhone used an operating system based on Mac OS X, which would later be called iPhone OS and then iOS. The simultaneous release of two operating systems based on the same frameworks placed tension on Apple, which cited the iPhone as forcing it to delay Mac OS X Leopard. However, after Apple opened the iPhone to third-party developers, its commercial success drew attention to Mac OS X, with many iPhone software developers showing interest in Mac development.
In 2007, Mac OS X Leopard released with universal binary components, allowing installation on both Intel Macs and select PowerPC Macs. It is also the final release with PowerPC Mac support. In 2009, Mac OS X Snow Leopard was the first version of Mac OS X to be built exclusively for Intel Macs and the final release with 32-bit Intel Mac support. The name was intended to signal its status as an iteration of Leopard, focusing on technical and performance improvements rather than user-facing features; indeed it was explicitly branded to developers as being a 'no new features' release. Since its release, several OS X or macOS releases follow this pattern, with a name derived from its predecessor, similar to the 'tick–tock model' used by Intel.
Starting in 2011 with Mac OS X Lion and OS X Mountain Lion, Apple moved some applications to a highly skeuomorphic style of design inspired by contemporary versions of iOS while simplifying some elements by making controls such as scroll bars fade out when not in use. This direction was, like brushed metal interfaces, unpopular with some users, although it continued a trend of greater animation and variety in the interface previously seen in design aspects such as the Time Machine backup utility, which presented past file versions against a swirling nebula, and the glossy translucent dock of Leopard and Snow Leopard. In addition, with Lion, Apple ceased to release separate server versions of Mac OS X, selling server tools as a separate downloadable application through the Mac App Store. A review described the trend in the server products as becoming "cheaper and simpler... shifting its focus from large businesses to small ones."
OS X
In 2012, with the release of OS X Mountain Lion, the name of the system was officially shortened from Mac OS X to OS X, after the previous version shortened the system name in a similar fashion a year prior. That year, Apple removed the head of OS X development, Scott Forstall, and design was changed towards a more minimal direction. Apple's new user interface design, using deep color saturation, text-only buttons and a minimal, 'flat' interface, was debuted with iOS 7 in 2013. With OS X engineers reportedly working on iOS 7, the version released in 2013, OS X Mavericks, was something of a transitional release, with some of the skeuomorphic design removed, while most of the general interface of Mavericks remained unchanged. The next version, OS X Yosemite, adopted a design similar to iOS 7 but with greater complexity suitable for an interface controlled with a mouse.From 2012 onwards, the system has shifted to an annual release schedule similar to that of Mac OS X releases prior to 10.4 Tiger. It also steadily cut the cost of updates from Snow Leopard onwards, before removing upgrade fees altogether in OS X Mavericks. Some journalists and third-party software developers have suggested that this decision, while allowing more rapid feature release, meant less opportunity to focus on stability, with no version of OS X recommendable for users requiring stability and performance above new features. Apple's 2015 update, OS X El Capitan, was announced to focus specifically on stability and performance improvements.