<P> From 2012 onwards, the system has shifted to an annual release schedule similar to that of iOS . It also steadily cut the cost of updates from Snow Leopard onwards, before removing upgrade fees altogether from 2013 onwards . 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 10.11 El Capitan, was announced to focus specifically on stability and performance improvements . </P> <P> In 2016, with the release of macOS 10.12 Sierra, the name was changed from OS X to macOS to streamline it with the branding of Apple's other primary operating systems: iOS, watchOS, and tvOS . macOS 10.12 Sierra's main features are the introduction of Siri to macOS, Optimized Storage, improvements to included applications, and greater integration with Apple's iPhone and Apple Watch . The Apple File System (APFS) was announced at the Apple Worldwide Developers Conference in 2016 as a replacement for HFS+, a highly criticized file system . At the 2017 Worldwide Developers Conference Apple previewed macOS 10.13 High Sierra . It uses APFS, rather than HFS+, on solid state drives . </P> <P> At macOS's core is a POSIX compliant operating system built on top of the XNU kernel, with standard Unix facilities available from the command line interface . Apple has released this family of software as a free and open source operating system named Darwin . On top of Darwin, Apple layered a number of components, including the Aqua interface and the Finder, to complete the GUI - based operating system which is macOS . </P> <P> With its original introduction as Mac OS X, the system brought a number of new capabilities to provide a more stable and reliable platform than its predecessor, the classic Mac OS . For example, pre-emptive multitasking and memory protection improved the system's ability to run multiple applications simultaneously without them interrupting or corrupting each other . Many aspects of macOS's architecture are derived from OPENSTEP, which was designed to be portable, to ease the transition from one platform to another . For example, NeXTSTEP was ported from the original 68k - based NeXT workstations to x86 and other architectures before NeXT was purchased by Apple, and OPENSTEP was later ported to the PowerPC architecture as part of the Rhapsody project . </P>

The most recent version of mac os is based on the ... operating system