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macOS, an abbreviation of Macintosh Operating System, is Apple Inc.'s operating system for Apple Macintosh computers, and is closely related to iOS, Apple's mobile operating system for its iPhone and iPod Touch product lines.

Originally known simply as "System" software, it shipped with the Macintosh 128K in January 1984 and became the first commercially successful operating system to use a purely graphical user interface. System 7.5 became known as Mac OS 7.5.1 during a software update in March 1995 and the name of the operating system was changed several times.

Retail box of Mac OS X 10.0

In December 1996, Apple Computer acquired NeXT, a startup by Apple co-founder Steve Jobs, for its software technology. Previous Macintosh system software releases became retroactively known as "classic" Mac OS while transitioning to Mac OS X, which was based on NeXTSTEP, a more robust operating system derived from Unix. Each successive release was nicknamed after a wild cat from Mac OS X 10.0 "Cheetah" until OS X 10.9 Mavericks, which officially dropped "Mac" from the name and started using names of natural landmarks in California. With macOS 10.12 "Sierra", the name returned to its roots, but in a style similar to Apple's mobile operating systems which were derived from macOS, such as iOS, iPadOS, tvOS, and watchOS. The most recent release is macOS 12 "Monterey".



History of macOS

The Macintosh operating system was originally developed by Bill Atkinson, Andy Hertzfeld, and Jef Raskin from 1979 to January 1984. There are a variety of views on how the underlying concepts of the Macintosh operating system had originated. The connection between the development of the Mac back to the Alto project at Xerox PARC has been widely documented, which in turn was itself inspired by Ivan Sutherland's Sketchpad and Doug Engelbart's oN-Line System, which pioneered the development of early graphical user interfaces.[1][2]


The Macintosh is based on a unique OS that, for the most part, was developed completely independently from the common operating systems of the time, requiring hardware and software designed specifically for use with the OS. Although this is useful for Apple products that run on the Mac OS, it could be frustrating for PC users because the Mac OS was not designed to be compatible with PC hardware or software. Since the Mac OS uses its own set of APIs (Application Programmable Interfaces), software using the system only has to call on one of the already defined APIs. This is what generally made PCs unable to use these types of software without emulation. However, Apple's transition to Intel processors have made the underlying hardware of recent Macintosh models more similar to PCs, allowing users to find solutions to run Windows natively on their Macs, and vice versa.


The Macintosh operating system was initially called System, as in "System 6". Apple deliberately played down the existence of the operating system in the early years of the Macintosh to help make the machine appear more user-friendly and to distance it from other systems such as CP/M and MS-DOS, which were portrayed as arcane and technically challenging. Apple wanted Macintosh to be portrayed as a system that would "just work" when you turned it on.

From its classic beginning, the Macintosh operating system introduced the "Toolbox", a collection of standardized routines that programs could call rather than accessing the computer hardware directly. This abstraction is what allowed Mac applications are written for one generation of the system to run on later generations: from the Mac Plus to the Mac II, to the PowerBook, to the Power Macintosh, for example. In the early days, Apple deliberately obscured the existence of an "operating system" to distance the Mac from other systems such as MS-DOS, which were portrayed as much harder to use in comparison. Terms such "system" and "the toolbox" were handy ways to refer to operating system services and the Macintosh APIs respectively that avoided technical jargon. Until the advent of the PowerPC G3 era systems (the so-called "new world" machines), large parts of the system were held in physical ROM on the motherboard, as well as other system components on disk that supplemented, overrode or patched the ROM routines. The purpose of this was to avoid using up too much of the limited storage of floppy disks for system support, given that the early Macs had no hard disk. In fact, one model of Mac was actually bootable using the ROM alone, the 1991 Macintosh Classic, which included a recovery partition in ROM.

Mac OS 7.5.1 was the first version to include the "Mac OS" logo (a blue smiley face). Mac OS 7.6 (which debuted in 1996) was the first version to be officially named Mac OS. This change in name came about because of the appearance of Mac "clones": workalike from other companies such as Power Computing and Motorola; Apple wanted to make it clear that the operating system was its own intellectual property.

The Mac OS can be divided into two families of operating systems:

  • Classic Mac OS, the system which shipped with the first Mac in 1984 and its descendants, culminating with Mac OS 9.
    • Classic Mac OS can be further subdivided into variants targeted at the Motorola 68000 family of processors (M68k), which included System 1 through Mac OS 8.1 and variants targeted at the Motorola RISC PowerPC processor, which included System 7.1 through Mac OS 9. Software that could run under either system was said to be "fat" (it included executable code for both architectures).
  • The newer Mac OS X (the "X" is pronounced ten, as in the Roman numeral). Mac OS X incorporates elements of BSD Unix, OpenStep, and Mac OS 9. Its low-level Unix-based foundation, Darwin, is open source.
    • Mac OS X can be further subdivided into variants targeted at the PowerPC architecture, which included Mac OS X Server 1.0 through Mac OS X 10.5, and the Intel x86 architecture, which includes Mac OS X 10.4 through to the present day. Software that could run under either system was said to be "Universal" (once again, it included executable code for both architectures).

Classic Mac OS

Desktop of System 1.0

Main article: Classic Mac OS

The "classic" Mac OS is characterized by its total lack of a command line; it is a completely graphical operating system. Heralded for its ease of use, it is also criticized for its cooperative multitasking, almost total lack of memory management, and susceptibility to extension conflicts. "Extensions" (originally called INITs) are program modules that extend the operating system, providing additional functionality (such as networking) or support for a particular device. Some extensions are prone not to work properly together or only when loaded in a particular order. Troubleshooting Mac OS extensions can be a time-consuming process of trial and error.

Desktop of Mac OS 9

Mac OS also introduced the Macintosh File System, followed by the more robust Hierarchical File System, an innovative system for storing digital files. Whereas a file on DOS or Unix would simply be a sequence of bytes written to disk, requiring an application to know which bytes represented code and which were graphic or other data, Mac files had two different "forks". In addition to the data fork, which contained a sequence of bytes, there was a resource fork which contained structured data such as menu definitions, graphics, sounds, or code segments. An application file might consist only of resources with no data fork. A text file might contain its text in the data fork and styling information in its resources so that an application which didn't recognize the styling information could still read the raw text. Despite the many assets of this arrangement, it became quite a challenge to interoperate with other operating systems which did not recognize such a file system layout; for example, copying a file from a Mac to DOS or Unix would strip it of its resource fork.

By the mid 1990s, it was clear the useful life of this 1980s-era technology was coming to an end, with other more stable multitasking operating systems being developed. In 1996, after some failed attempts to build a "next-generation" operating system in-house, Apple bought NeXT in order to use its operating system to accelerate the development of a modern operating system.

Mac OS X

10.9 "Mavericks" is the first version of Mac OS X not to be named after a cat.

Main article: Mac OS X

Mac OS X brought Unix-style memory management and pre-emptive multitasking to the Mac platform. Vastly improved memory management allowed more programs to run at once and virtually eliminated the possibility of one program crashing another. It is also the first Mac OS to include a command line outside of developer's tools, although this is never seen unless the user launches a "terminal" program.

Since these new features put higher demands on system resources, Mac OS X is only officially supported on PowerPC G3 and newer processors. Even then, it runs slowly on older G3 systems. Interestingly, every update to Mac OS X from the original public beta through Mac OS X 10.6 has had the peculiar quality of being noticeably faster and more responsive than the version it replaced, the opposite trend of most operating systems.

Mac OS X, from the Public Beta through Mac OS X 10.4 had a compatibility layer for running older Mac applications, the Classic Environment (known to programmers as "the blue box"). This runs a full copy of the older Mac OS 9.x as a Mac OS X process. Most well-written "classic" applications function properly under this environment, but compatibility is only assured if the software was written to be unaware of the actual hardware and to interact solely with the operating system.

Many fans of the original Mac OS accepted OS X, but a few criticized it as being more difficult to operate and less user-friendly than the original Mac OS.

From Mac OS X 10.4 (Intel) through Mac OS X 10.6, the OS had a second compatability layer named Rosetta for running PowerPC applications inside an x86-based OS X.

Mac OS technologies

  • QuickDraw: the imaging model which first provided mass-market WYSIWYG
  • Finder: the interface for browsing the filesystem and launching applications
  • MultiFinder: the first version to support simultaneously running multiple apps
  • Chooser: tool for accessing network resources (e.g., enabling AppleTalk)
  • ColorSync: technology for ensuring appropriate color matching
  • Mac OS memory management: how the Mac managed RAM and virtual memory before the switch to UNIX
  • PowerPC emulation of Motorola 68000: how the Mac handled the architectural transition from CISC to RISC (see Mac 68k emulator)
  • Desk Accessories: small "helper" apps that could be run concurrently with any other app, prior to the advent of MultiFinder or System 7.
  • PlainTalk: speech synthesis and speech recognition technology
  • Mac-Roman: Character set

See also


  1. A Talk by Alan Kay by Noah Wardrip-Fruin & Nick Montfort, theNEWMEDIAREADER. 2003.
  2. 50 Years After 'As We May Think': The Brown/MIT Vannevar Bush Symposium by Rosemary Simpson, Allen Renear, Elli Mylonas, and Andries van Dam, ACM Interactions. 1996.

External Links


Mac OS.png   Classic Mac OS versions
Macintosh System Software : System 1 · System 2 · System 3 · System 4 · System 5 · System 6 · System 7
Mac OS : Mac OS 7.6 · Mac OS 8 · Mac OS 9 · Classic environment
Cancelled : Copland · Gershwin
Deprecated in in May 2002 and succeeded by Mac OS X
Mac OS X.png   Mac OS X / macOS versions
Mac OS X Server : Server 1 (Rhapsody / Hera)
Mac OS X Developer Preview : DP1 | DP2 | DP3 | DP4
Mac OS X Public Beta : Public Beta (Kodiak)
Mac OS X 10.0 (Cheetah) : 10.0.0 | 10.0.1 | 10.0.2 | 10.0.3 | 10.0.4
Mac OS X 10.1 (Puma) : 10.1.0 | 10.1.1 | 10.1.2 | 10.1.3 | 10.1.4 | 10.1.5
Mac OS X 10.2 (Jaguar) : 10.2.0 | 10.2.1 | 10.2.2 | 10.2.3 | 10.2.4 | 10.2.5 | 10.2.6 | 10.2.7 | 10.2.8 (G3 / G4 · G5)
Mac OS X 10.3 (Panther) : 10.3.0 | 10.3.1 | 10.3.2 | 10.3.3 | 10.3.4 | 10.3.5 | 10.3.6 | 10.3.7 | 10.3.8 | 10.3.9
Mac OS X 10.4 (Tiger) : 10.4.0 | 10.4.1 | 10.4.2 | 10.4.3 | 10.4.4 | 10.4.5 | 10.4.6 | 10.4.7 | 10.4.8 | 10.4.9 | 10.4.10 | 10.4.11
Mac OS X 10.5 (Leopard) : 10.5.0 | 10.5.1 | 10.5.2 | 10.5.3 | 10.5.4 | 10.5.5 | 10.5.6 | 10.5.7 | 10.5.8 | 10.5.9 (PPC)
  Mac OS X 10.6 (Snow Leopard) : 10.6.0 | 10.6.1 | 10.6.2 | 10.6.3 | 10.6.4 | 10.6.5 | 10.6.6 | 10.6.7 | 10.6.8
Mac OS X 10.7 (Lion) : 10.7.0 | 10.7.1 | 10.7.2 | 10.7.3 | 10.7.4 | 10.7.5
  Mac OS X 10.8 (Mountain Lion) : 10.8.0 | 10.8.1 | 10.8.2 | 10.8.3 | 10.8.4 | 10.8.5
OS X 10.9 (Mavericks) : 10.9.0 | 10.9.1 | 10.9.2 | 10.9.3 | 10.9.4 | 10.9.5
OS X 10.10 (Yosemite) : 10.10.0 | 10.10.1 | 10.10.2 | 10.10.3 | 10.10.4 | 10.10.5
OS X 10.11 (El Capitan) : 10.11.0 | 10.11.1 | 10.11.2 | 10.11.3 | 10.11.4 | 10.11.5 | 10.11.6
macOS 10.12 (Sierra) : 10.12.0 | 10.12.1 | 10.12.2 | 10.12.3 | 10.12.4 | 10.12.5 | 10.12.6
macOS 10.13 (High Sierra) : 10.13.0 | 10.13.1 | 10.13.2 | 10.13.3 | 10.13.4 | 10.13.5 | 10.13.6
macOS 10.14 (Mojave) : 10.14.0 | 10.14.1 | 10.14.2 | 10.14.3 | 10.14.4 | 10.14.5 | 10.14.6
macOS 10.15 (Catalina) : 10.15.0 | 10.15.1 | 10.15.2 | 10.15.3 | 10.15.4 | 10.15.5 | 10.15.6 | 10.15.7
macOS 11 (Big Sur) : 11.0 · 11.0.1 | 11.1 | 11.2 · 11.2.1 · 11.2.2 · 11.2.3 | 11.3 · 11.3.1 | 11.4 | 11.5 · 11.5.1 · 11.5.2 | 11.6 · 11.6.1 · 11.6.2 · 11.6.3 · 11.6.4 · 11.6.5 · 11.6.6 · 11.6.7
macOS 12 (Monterey) : 12.0 · 12.0.1 | 12.1 | 12.2 · 12.2.1 | 12.3 · 12.3.1 | 12.4 | 12.5
macOS 13 (Ventura) : 13.0
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