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. Development NeXTSTEP NeXTSTEP used a hybrid kernel that combined the Mach 2.5 kernel developed at Carnegie Mellon University with subsystems from 4.3BSD. NeXTSTEP also introduced a new windowing system based on Display PostScript that intended to achieve better WYSIWYG systems by using the same language to draw content on monitors that drew content on printers. 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. NeXTSTEP originally ran on Motorola's 68k processors, but was later ported to Intel's x86, Hewlett-Packard's PA-RISC and Sun Microsystems' SPARC processors. Later on, the developer tools and frameworks were