Architecture of macOS

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.

NeXT also included object-oriented programming tools based on the Objective-C language that they had acquired from Stepstone and a collection of Frameworks (or Kits) that were intended to speed software development.

[1] The Objective-C developer tools and Frameworks were referred to as the Yellow Box and also made available separately for Microsoft Windows.

At this WWDC, Apple also showed Mac OS X booting off of a HFS Plus formatted drive for the first time.