Additional diagram of macOS architecture (2017 update)
The architecture of macOS describes the layers of the operating system that is the culmination of Apple Inc.'s decade-long research and development process to replace the classic Mac OS.
After the failures of their previous attempts—Pink, which started as an Apple project but evolved into a joint venture with IBM called Taligent, and Copland, which started in 1994 and was cancelled two years later—Apple began development of Mac OS X, later renamed OS X and then macOS, with the acquisition of NeXT's NeXTSTEP in 1997.
