Mac OS

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For the American humanities teaching program usually called "MACOS", see Man: A Course of Study.
Mac OS
OS X El Capitan logo.svg
Screenshot of OS X v10.11 El Capitan
Developer Apple, NeXT
Written in {{#property:p277}}
OS family Classic Mac OS (System 1–7, Mac OS 8–9)
Unix, Mach and FreeBSD (OS X)[1][2][3]
Working state Publicly released
Source model Classic Mac OS: Closed source
OS X: Closed source (with open-source components)
Initial release Classic Mac OS: January 24, 1984; 33 years ago (1984-01-24)
OS X: September 13, 2000; 17 years ago (September 13, 2000) (as Mac OS X)
Latest release 10.11.4 (Build 15E65) / March 21, 2016; 17 months ago (2016-03-21)
Latest preview 10.11.6 Beta 1 (15G7a) (May 23, 2016; 15 months ago (2016-05-23)) [±]
Kernel type Classic Mac OS: Monolithic
OS X: Hybrid (XNU)
License Proprietary
Official website

Mac OS is a series of graphical user interface–based operating systems developed by Apple Inc. for their Macintosh line of computer systems.

The original operating system was first introduced in 1984 as being integral to the original Macintosh, and referred to as the "System". Referred to by its major revision starting with "System 6" and "System 7", Apple rebranded version 7.6 as "Mac OS" as part of their Macintosh clone program in 1996. The Macintosh, specifically its system software, is credited with having popularized the early graphical user interface concept.

There are two architectural legacies of Mac OS. Up to major revision 9, from 1984 to 2000, it is historically known as Classic Mac OS. Major revision 10, from 2001 to present, is branded OS X (originally referred to as Mac OS X).[4] Both legacies share a general interface design, and there has been some overlap of application frameworks for compatibility; but the two systems have different origins and use deeply different architectures.

Design concept

Apple's original concept for the Macintosh deliberately sought to minimize the user's conceptual awareness of the operating system. Many basic tasks that had required more operating system knowledge on other systems could then be accomplished by mouse gestures and graphic controls on a Macintosh. This would differentiate it from its contemporaries such as MS-DOS, which use a command-line interface consisting of tersely abbreviated textual commands.

The core of the system software of early Macintoshes is held in ROM, with updates originally provided on floppy disk, freely copyable at Apple dealers. The user's involvement in an upgrade of the operating system is also minimized to running an installer, or replacing system files using the file manager.


Early versions of Mac OS are compatible only with Motorola 68000-family Macintoshes. As Apple introduced computers with PowerPC hardware, the OS was ported to support this architecture. Mac OS 8.1 is the last version that could run on a "68K" processor (the 68040). OS X, which has superseded the "Classic" Mac OS, is compatible with only PowerPC processors from version 10.0 ("Cheetah") to version 10.3 ("Panther"). Both PowerPC and Intel processors are supported in version 10.4 ("Tiger", Intel only supported after an update) and version 10.5 ("Leopard"). 10.6 and later versions support only Intel processors.[5]

The early Macintosh operating system consists of two user-visible components, called "System" and "Finder", each with its own version number.[6] Starting with version 5, both are incorporated under a single "System Software" moniker. System 7.5.1 is the first to include the Mac OS logo (a variation on the original Happy Mac startup icon), and Mac OS 7.6 is the first to be named "Mac OS". These changes were made during the era of Macintosh clones, to disassociate the operating system from Apple's own Macintosh models.[7]

In systems prior to PowerPC G3-based systems, significant parts of the system are stored in physical ROM on the motherboard. The initial purpose of this is to avoid using up the limited storage of floppy disks on system support, given that the early Macs have no hard disk (only one model of Mac was ever actually bootable using the ROM alone, the 1991 Mac Classic model). This architecture also allows for a completely graphical OS interface at the lowest level without the need for a text-only console or command-line mode: boot time errors, such as finding no functioning disk drives, are communicated to the user graphically, usually with an icon or the distinctive Chicago bitmap font and a Chime of Death or a series of beeps. This is in contrast to MS-DOS and CP/M computers of the time, which display such messages in a mono-spaced font on a black background, and require the use of the keyboard rather than a mouse, for input. To provide such niceties at a low level, early Mac OS depends on core system software in ROM on the motherboard, which also ensure that only Apple computers or licensed clones (with the copyright-protected ROMs from Apple) can run Mac OS.

"Classic" Mac OS (1984–2001)

Main article: History of Mac OS
File:Apple Macintosh Desktop.png
Original 1984 Macintosh desktop

The "classic" Mac OS is characterized by its monolithic system. Versions of Mac OS up through System 4 ran only one application at a time. Even so, it was noted for its ease of use. Mac OS gained cooperative multitasking with System 5, which ran on the Macintosh SE and Macintosh II. It was criticized for its very limited memory management, lack of protected memory, no access controls, and susceptibility to conflicts among operating system "extensions" that provide additional functionality (such as networking) or support for a particular device. Some extensions didn't work properly together, or worked only when loaded in a particular order. Troubleshooting Mac OS extensions could be a time-consuming process of bisecting and trial and error.

The Macintosh originally used the Macintosh File System (MFS), a flat file system with only one level of folders. This was quickly replaced in 1985 by the Hierarchical File System (HFS), which had a true directory tree. Both file systems are otherwise compatible.

Files in most file systems used with DOS, Windows, Unix, or other operating systems have only one "fork". By contrast, MFS and HFS give files two different "forks". The data fork contains the same sort of information as a file in other file systems, such as the text of a document or the bitmaps of an image file. The resource fork contains other structured data such as menu definitions, graphics, sounds, or code segments that would be incorporated into a program's file format on other systems. An executable file might consist only of resources (including code segments) with an empty data fork, while a data file might have only a data fork with no resource fork. A word processor file could contain its text in the data fork and styling information in the resource fork, so that an application which doesn’t recognize the styling information can still read the raw text.

On the other hand, these forks would provide a challenge to interoperability with other operating systems. In copying or transferring a MacOS file to a non-Mac system, the default implementations would simply strip the file of its resource fork. Most data files contained only nonessential information in their resource fork, such as window size and location, but program files would be inoperative without their resources. This necessitated such encoding schemes as BinHex and MacBinary, which allowed a user to encode a dual-forked file into a single stream, or inversely take a single stream so-encoded and reconstitute it into a dual-forked file usable by MacOS.

PowerPC versions of OS X up to and including OS X v10.4 Tiger include a compatibility layer for running older Mac applications, the Classic Environment. This runs a full copy of the older Mac OS, version 9.1 or later, in an OS X process. Early New World PowerPC-based Macs shipped with Mac OS 9.2 as well as OS X. Mac OS 9.2 had to be installed by the user – it was not installed by default on hardware revisions released after the release of OS X 10.4 Tiger. Most well-written "classic" applications function properly under this environment, but compatibility is assured only if the software was written to be unaware of the actual hardware, and to interact solely with the operating system. The Classic Environment is not available on Intel-based Macintosh systems due to the incompatibility of Mac OS 9 with the x86 hardware.

Users of the classic Mac OS generally upgraded to OS X, but many criticized it as being more difficult and less user-friendly than the original Mac OS, for the lack of certain features that had not been re-implemented in the new OS, or for being slower on the same hardware (especially on older hardware), or other, sometimes serious incompatibilities with the older OS.[8] Because drivers (for printers, scanners, tablets, etc.) written for the older Mac OS are not compatible with OS X, and due to the lack of OS X support for older Apple machines, a significant number of Macintosh users continued using the older classic Mac OS.

In June 2005, Steve Jobs announced at the Apple Worldwide Developers Conference keynote that Apple computers would be transitioning from PowerPC to Intel processors and thus dropping compatibility on new machines for Mac OS Classic. At the same conference, Jobs announced Developer Transition Kits that included beta versions of Apple software including OS X that developers could use to test their applications as they ported them to run on Intel-powered Macs. In January 2006, Apple released the first Macintosh computers with Intel processors, an iMac and the MacBook Pro, and in February 2006, Apple released a Mac mini with an Intel Core Solo and Duo processor. On May 16, 2006, Apple released the MacBook, before completing the Intel transition on August 7 with the Mac Pro. To ease the transition for early buyers of the new machines, Intel-based Macs included an emulation technology called Rosetta, which allows them to run OS X software that was compiled for PowerPC-based Macintosh models. Rosetta runs transparently, creating a user experience identical to running the software on a PowerPC machine, though execution is typically slower than with native code. Rosetta was an optional installation in OS X 10.6 Snow Leopard and is not available at all in OS X 10.7 Lion.


Main article: OS X

OS X, introduced as Mac OS X in 2001 and renamed OS X in 2012, is the latest version of Apple's operating system. Although it is officially designated as simply "version 10" of Mac OS, it has a history largely independent of the earlier Mac OS releases. Major revisions to Mac OS are now issued as point revisions, such that, for example, 10.2 is substantially different from 10.5.

The OS X architectural legacy is the successor to Mac OS 9 and the "classic" Mac OS legacy. It is however a Unix operating system, based on the NeXTSTEP operating system which Apple acquired after purchasing NeXT Computer – with its CEO Steve Jobs returning to Apple at that time. OS X also makes use of the BSD codebase and the XNU kernel.[9] There have been twelve significant releases of OS X, the most recent being OS X 10.11, referred to as "El Capitan". Prior to 10.11 came OS X 10.10 "Yosemite", 10.9 "Mavericks", 10.8 "Mountain Lion", 10.7 "Lion", 10.6 "Snow Leopard", 10.5 "Leopard", 10.4 "Tiger", 10.3 "Panther", 10.2 "Jaguar", 10.1 ("Puma"), and 10.0 ("Cheetah").

OS X has six significant releases as OS X Server. The first of these, Mac OS X Server 1.0, was released in beta before the client version in 1999. The server versions are architecturally identical to the client versions, with the differentiation found in their inclusion of tools for server management, including tools for managing OS X-based workgroups, mail servers, and web servers, amongst other tools. As of the name change to OS X, OS X Server is no longer sold as a separate operating system product. The server tools could then be added to the singular OS X product, giving the same functionality.

OS X Server is available as an operating system to-order on Mac Mini and Mac Pro computers as a part of a server package. Unlike the client version, OS X Server can be run in a virtual machine using emulation software such as Parallels Desktop for Mac and VMware Fusion.

OS X was used as the basis for iOS, (originally iPhone OS) used on Apple's iPhone, iPod Touch, and iPad;[10] iOS is, in turn the basis of watchOS, used on the Apple Watch, the "Apple TV Software" on the second-generation and third-generation Apple TV, and tvOS, used on the fourth-generation Apple TV.

Star Trek

Main article: Star Trek project

Star Trek (as in "to boldly go where no Mac has gone before") was a relatively unknown secret prototype beginning in 1992, whose goal was to create a version of the classic Mac OS that would run on Intel-compatible x86 personal computers. In partnership with Apple and with support from Intel, the project was instigated by Novell, which was looking to integrate its DR-DOS with the Mac OS GUI as a mutual response to the monopoly of Microsoft's Windows 3.0 and MS-DOS. A team consisting of four from Apple and four from Novell was able to get the Macintosh Finder and some basic applications such as QuickTime, running smoothly on the x86 architecture. The project was canceled only one year later in early 1993. Some of the code from this effort was reused later when porting the Mac OS to PowerPC.[11][12]

68k emulation

Although the Star Trek software was never released, third-party Macintosh emulators, such as vMac, Basilisk II, and Executor, eventually made it possible to run the classic Mac OS on Intel-based PCs. These emulators were restricted to emulating the 68000 series of processors, and as such most couldn't run versions of the Mac OS that succeeded 8.1, which required PowerPC processors. Most also required a Mac ROM image or a hardware interface supporting a real Mac ROM chip; those requiring an image are of dubious legal standing as the ROM image may infringe on Apple's intellectual property.

A notable exception was the Executor commercial software product from Abacus Research & Development, the only product that used 100% reverse engineered code without the use of Apple technology. It ran extremely quickly but never achieved more than a minor subset of functionality. Few programs were completely compatible and many were extremely crash-prone if they ran at all. Executor filled a niche market for porting 68k Mac applications to x86 platforms; development ceased in 2002 and the source code was released by the author in late 2008.[13]

Emulators using Mac ROM images offered near complete Mac OS compatibility and later versions offered excellent performance as modern x86 processor performance increased exponentially.

Most of the Mac user base had already started moving to the PowerPC platform that offered backward compatibility on 8.xx & 9.xx operating systems along with faster PowerPC software support. This helped ease the transition to PowerPC-only applications while prematurely obsolescing 68k emulators and the Classic-only applications they supported well before these emulators were refined enough to compete with a real Mac.

PowerPC emulation

At the time of 68k-emulator development, PowerPC support was difficult to justify not only due to the emulation code itself but also the anticipated wide performance overhead of an emulated PowerPC architecture vs. a real PowerPC based Mac. This would later prove correct with the start of the PearPC and project even years later despite the availability of 7th & 8th generation x86 processors employing similar architecture paradigms present in the PowerPC.[citation needed] Many application developers were also creating and releasing both 68k and PowerPC versions concurrently helping to negate the need for PowerPC emulation. PowerPC Mac users who could technically run either obviously chose the faster PowerPC applications. By 1995 Apple was no longer selling 68k-based Macs and the existing installed base quickly evaporated.

The PearPC emulator is capable of emulating the PowerPC processors required by newer versions of the Mac OS (like OS X). Unfortunately, it is no longer maintained and, like many emulators, tends to run much slower than a native operating system would.[citation needed]

During the transition from PowerPC to Intel processors, Apple realized the need to incorporate a PowerPC emulator into OS X in order to protect its customers' investments in software designed to run on the PowerPC. Apple's solution is an emulator called Rosetta. Prior to the announcement of Rosetta, industry observers assumed that any PowerPC emulator running on an x86 processor would suffer a heavy performance penalty (e.g., PearPC's slow performance). Rosetta's relatively minor performance penalty therefore took many by surprise.

Another PowerPC emulator is SheepShaver, which has been around since 1998 for BeOS on the PowerPC platform, but in 2002 was open sourced, and efforts began to port it to other platforms. Originally it was not designed for use on x86 platforms and required an actual PowerPC processor present in the machine it was running on similar to a hypervisor. Although it provides PowerPC processor support, it can run only up to Mac OS 9.0.4 because it does not emulate a memory management unit.

Other examples include ShapeShifter (by the same programmer that conceived SheepShaver), Fusion and iFusion. The latter ran classic Mac OS with a PowerPC "coprocessor" accelerator card. Using this method has been said to equal or better the speed of a Macintosh with the same processor, especially with respect to the m68k series due to real Macs running in MMU trap mode, hampering performance.

Macintosh clones

Main article: Macintosh clone

Several computer manufacturers over the years have made Macintosh clones capable of running Mac OS. From 1995 to 1997 Apple licensed Macintosh ROMs to several companies, notably Power Computing, UMAX and Motorola. These machines normally ran various versions of classic Mac OS. Steve Jobs ended the clone-licensing program after returning to Apple in 1997.

In 2008, Miami-based manufacturing company Psystar Corporation announced a $399 clone called OpenMac that came with a barebones system that can run Mac OS X 10.5 Leopard. Threatened with litigation, Psystar changed the name to Open Computer. Apple filed a lawsuit with the company and asked that Psystar be ordered to stop producing clone systems, recall every system sold, and pay monetary damages.[14] Eventually, Apple prevailed in court, and the Open Computer's production was ceased. Psystar itself appears to be defunct now, as the company's website is gone.

Mac OS on non-Apple-labeled computers

Main article: OSx86

Although a violation of Apple's EULA,[15] running OS X operating systems compiled for x86 or x86_64 ("Intel 64") on a non-Apple PC is possible using several approaches.

Installation of Mac OS X requires a Mac OS X Installer emulator, the most straightforward of which is a USB flash drive–type Installer emulator. Once the installation has been successfully completed to the hard drive, the hard drive may be booted using the emulator portion of the USB flash drive as a "helper" and a boot loader Installer may be downloaded and used to place the boot loader on the hard drive's boot blocks. Thereafter, Mac OS X may be booted from the hard drive alone; the installed boot loader takes care of any required device injection and/or kernel patching.

Mac OS X is generally compatible with any Intel desktop-based system or Intel-based motherboard, ICH6 or later,[16] however compatibility past Snow Leopard cannot be assured with ICH6. Compatibility with ICH7 and with Lion and 945 (G)MCH has already been demonstrated and proven. Compatibility with ICH7 or later and any associated MCH/(G)MCH is quite good, certainly including Lion, and possibly also including Mountain Lion.

Mac OS X compatibility with Intel laptop- or netbook-based systems is quite variable but has been successful on a few Intel Atom-based netbooks.


Main article: A/UX

In 1988, Apple released its first UNIX-based OS, A/UX, which was a UNIX operating system with the Mac OS look and feel. It was not very competitive for its time, due in part to the crowded UNIX market and Macintosh hardware lacking high-end design features present on workstation-class computers. A/UX had most of its success in sales to the U.S. government, where POSIX compliance was a requirement that Mac OS could not meet.


The Macintosh Application Environment (MAE) was a software package introduced by Apple Computer in 1994 which allowed users of certain Unix-based computer workstations to run Apple Macintosh application software.

MAE used the X Window System to emulate a Macintosh Finder-style graphical user interface. The last version, MAE 3.0, was compatible with System 7.5.3.

MAE was available for Sun Microsystems SPARCstation and Hewlett-Packard systems. It was discontinued on May 14, 1998.


Main article: MkLinux

Announced at The 1996 World Wide Developers Conference (WWDC), MkLinux is an open source computer operating system started by the OSF Research Institute and Apple Computer in February 1996 to port Linux to the PowerPC platform, and thus Macintosh computers. In the summer of 1998, the community-led MkLinux Developers Association took over development of the operating system. MkLinux is short for "Microkernel Linux," which refers to the project's adaptation of the Linux kernel to run as a server hosted atop the Mach microkernel. MkLinux is based on version 3.0 of Mach.


  1. "The Open Brand – Register of Certified Products – OS X 10.5 on Intel-based Macintosh computers". The Open Group. Retrieved November 22, 2009. 
  2. "The Open Brand – Register of Certified Products – OS X 10.6 on Intel-based Macintosh computers". The Open Group. Retrieved November 22, 2009. 
  3. "Apple page on UNIX". Apple Inc. Retrieved November 5, 2008. 
  4. Patel, Nilay (February 16, 2012). "Apple officially renames Mac OS X to OS X, drops the 'Mac'". The Verge. Retrieved February 21, 2012. 
  5. "OS X 10.6 Snow Leopard Installation and Setup Guide" (PDF). Apple Inc. Retrieved April 6, 2010. 
  6. "Official Apple Support". 
  7. "System 7.5 and Mac OS 7.6: The Beginning and End of an Era". Mac OS 7.6 deserves some special mention. The most obvious difference is the name change; this was for the Mac clone manufacturers, who weren’t making Macintoshes but “Mac OS Computers”. 
  8. "OS X 10.1". 
  9. "Mac OS X: What is BSD?". 
  10. "What operating system does the iPhone use? Can it run MacOS X applications like Skype and Photoshop?". July 5, 2010. Retrieved April 4, 2014. 
  11. Hormby, Tom (2005). "Star Trek: Apple's First Mac OS on Intel Project". Retrieved November 10, 2015. 
  12. Linzmayer, Owen W. (1999). Apple Confidential (PDF). San Francisco, CA: No Starch Press. ISBN 9781886411289. OCLC 245921029. Retrieved March 21, 2013. 
  13. "Executor source code". 
  14. Paul McDougall (July 16, 2008). "Apple Demands Recall Of Psystar Mac Clones". InformationWeek. Retrieved December 30, 2010. 
  15. "Software License Agreement For OS X" (PDF). Apple, Inc. Retrieved May 10, 2010. This License allows you to install, use and run one (1) copy of the Apple Software on a single Apple-labeled computer at a time. You agree not to install, use or run the Apple Software on any non-Apple-labeled computer, or to enable others to do so.  line feed character in |quote= at position 159 (help)
  16. Apple Inc's Intel "Proof of Concept" motherboard was 945 (G)MCH- and ICH6-based.

External links