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Thearchitecture ofmacOS describes the layers of theoperating system that is the culmination ofApple Inc.'s decades-long research and development process to replace theclassic Mac OS.
After the failures of their previous attempts—Pink, which started as an Apple project but evolved into a joint venture withIBM calledTaligent, andCopland, 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 ofNeXT'sNeXTSTEP in 1997.
NeXTSTEP used a hybrid kernel that combined theMach 2.5 kernel developed atCarnegie Mellon University with subsystems from4.3BSD. NeXTSTEP also introduced a new windowing system based onDisplay PostScript that intended to achieve betterWYSIWYG systems by using the same language to draw content on monitors that drew content on printers. NeXT also includedobject-oriented programming tools based on theObjective-C language that they had acquired fromStepstone and a collection of Frameworks (or Kits) that were intended to speed software development. NeXTSTEP originally ran onMotorola's68k processors, but was later ported toIntel'sx86,Hewlett-Packard'sPA-RISC andSun Microsystems'SPARC processors. Later on, the developer tools and frameworks were released, asOpenStep, as a development platform that would run on other operating systems.
On February 4, 1997, Apple acquired NeXT and began development of theRhapsody operating system. Rhapsody built on NeXTSTEP,porting the core system to thePowerPC architecture and adding a redesigned user interface based on thePlatinum user interface fromMac OS 8. An emulation layer calledBlue Box allowed Mac OS applications to run within an actual instance of the Mac OS and an integratedJava platform.[1] The Objective-C developer tools and Frameworks were referred to as theYellow Box and also made available separately forMicrosoft Windows. The Rhapsody project eventually bore the fruit of all Apple's efforts to develop a new generation Mac OS, which finally shipped in the form ofMac OS X Server.
At the 1998Worldwide Developers Conference (WWDC), Apple announced a move that was intended as a response to complaints from Macintosh software developers who were not happy with the two options (Yellow Box and Blue Box) available in Rhapsody. Mac OS X would add another developerAPI to the existing ones in Rhapsody. Key APIs from theMacintosh Toolbox would be implemented in Mac OS X to run directly on the BSD layers of the operating system instead of in the emulated Macintosh layer. This modified interface, calledCarbon, would eliminate approximately 2000 troublesome API calls (of about 8000 total) and replace them with calls compatible with a modern OS.[2]
At the same conference, Apple announced that the Mach side of the kernel had been updated with sources from theOSF MK 7.3 (Open Source Foundation's MK operating system)[3] and the BSD side of the kernel had been updated with sources from theFreeBSD,NetBSD andOpenBSD projects.[2] They also announced a new driver model called I/O Kit, intended to replace the Driver Kit used in NeXTSTEP citing Driver Kit's lack of power management and hot-swap capabilities and its lack of automatic configuration capability.[4]
At the 1999 WWDC, Apple revealedQuartz, a newPortable Document Format (PDF) based windowing system for the operating system that was not encumbered with licensing fees toAdobe like the Display PostScript windowing system of NeXTSTEP. Apple also announced that the Yellow Box layer had been renamedCocoa and began to move away from their commitment to providing the Yellow Box on Windows. At this WWDC, Apple also showed Mac OS X booting off of aHFS Plus formatted drive for the first time.
The first public release of Mac OS X released to consumers was aPublic Beta released on September 13, 2000.
