Architecture of Mac OS X

Mac OS X is the culmination of Apple Inc.'s decade-long search for an operating system to replace the original 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 that started in 1994 and was cancelled two years later, Apple began development of their most recent operating system (Mac OS X) with the acquisition of NeXT's NEXTSTEP.

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 released, as OpenStep, as a development platform that would run on other operating systems.

Rhapsody

On February 4, 1997, Apple acquired NeXT and began development of the Rhapsody operating system. Rhapsody built on NEXTSTEP, porting the core system to the PowerPC architecture and adding a redesigned user interface based on the Platinum user interface from Mac OS 8. An emulation layer called Blue Box allowed Mac OS applications to run within an actual instance of the Mac OS and an integrated Java platform. [cite web | url=http://web.archive.org/web/19981202202310/http://product.info.apple.com/pr/press.releases/1998/q1/971119.pr.rel.macos.html | title=Apple Extends Rhapsody Developer Release with Mac OS Compatibility Environment, Code-Named "Blue Box" | date=1997-11-19 | author=Apple PR | publisher=apple.com | accessdate=2006-10-13] The Objective-C developer tools and Frameworks were referred to as the Yellow Box and also made available separately for Microsoft Windows. The Rhapsody project eventually bore the fruit of all Apple's efforts to develop a new generation Macintosh OS, which finally shipped in the form of Mac OS X Server.

Mac OS X

At the 1998 Worldwide 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 developer API to the existing ones in Rhapsody. Key APIs from the Macintosh 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, called Carbon, would eliminate approximately 2000 troublesome API calls (of about 8000 total) and replace them with calls compatible with a modern OS.cite web | url=http://www.stepwise.com/SpecialCoverage/WWDC98/Summary.html | title=WWDC 98 Summary | author=Scott Anguish | date=May 1998 | publisher=stepwise.com | accessdate=2006-10-13]

At the same conference, Apple announced that the Mach side of the kernel had been updated with sources from version 3 of the Mach kernel and the BSD side of the kernel had been updated with sources from the FreeBSD, NetBSD and OpenBSD projects. 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. [cite web | url=http://www.stepwise.com/SpecialCoverage/WWDC98/Thursday-IOKit.html | title=Rhapsody Core OS: Intro to the I/O Driver Architecture | author=Scott Anguish | date=1998-05-14 | publisher=stepwise.com | accessdate=2006-10-13 ]

At the 1999 WWDC, Apple revealed Quartz, a new Portable Document Format (PDF) based windowing system for the operating system that wasn't encumbered with licensing fees to Adobe like the Display PostScript windowing system of NEXTSTEP. Apple also announced that the Yellow Box layer had been renamed Cocoa 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 a HFS Plus formatted drive for the first time.

The first public release of Mac OS X released to consumers was a Public Beta released on September 13 2000.

References

External links

* [http://www.apple.com/macosx/ Apple: Mac OS X] — The official page for Mac OS X.
* [http://www.kernelthread.com/mac/osx/ What is Mac OS X? (kernelthread.com)] — An overview of the Mac OS X operating system architecture
* [http://arstechnica.com/reviews/os/macosx-10.4.ars/2 Mac OS X (arstechnica.com)] — Comprehensive reviews of Mac OS X (all versions)
* [http://www.osxbook.com/ Mac OS X Internals] The web page associated with the book.