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Mac OS logo imageMac OS is the trademarked name for a series of graphical user interface-based operating systems developed by Apple Inc. (formerly Apple Computer, Inc.) for their Macintosh line of computer systems. The Macintosh user experience is credited with popularizing the graphical user interface. The original form of what Apple would later name the "Mac OS" was the integral and unnamed system software first introduced in 1984 and later in 1997 with the original Macintosh, usually referred to simply as the System software.

Apple deliberately downplayed 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 operating systems such as MS-DOS, which were portrayed as arcane and technically challenging. Much of this early system software was held in ROM, with updates typically provided free of charge by Apple dealers on floppy disk. As increasing disk storage capacity and performance gradually eliminated the need for fixing much of an advanced GUI operating system in ROM, Apple explored cloning while positioning major operating system upgrades as separate revenue-generating products, first with System 7 and System 7.5, then with Mac OS 7.6 in 1997.

Earlier versions of the Mac OS were compatible only with Motorola 68000-based Macintoshes. As Apple introduced computers with PowerPC hardware, the OS was upgraded to support this architecture as well. Mac OS X, which has superseded the "Classic" Mac OS, is compatible with both PowerPC and Intel processors.


The early Macintosh operating system initially consisted of two pieces of software, called "System" and "Finder", each with its own version number. System 7.5.1 was the first to include the Mac OS logo (a variation on the original "Happy Mac" smiley face Finder startup icon), and Mac OS 7.6 was the first to be named "Mac OS" (to ensure that users would still identify it with Apple, even when used in "clones" from other companies.

Until the advent of the later PowerPC G3-based systems, significant parts of the system were stored in physical ROM on the motherboard. The initial purpose of this was to avoid using up the limited storage of floppy disks on system support, given that the early Macs had no hard disk. (Only one model of Mac was ever actually bootable using the ROM alone, the 1991 Mac Classic model.) This architecture also allowed for a completely graphical OS interface at the lowest level without the need for a text-only console or command-line mode. A fatal software error, or even a low-level hardware error discovered during system startup (such as finding no functioning disk drives), was communicated to the user graphically using some combination of icons, alert box windows, buttons, a mouse pointer, and the distinctive Chicago bitmap font. Mac OS depended on this core system software in ROM on the motherboard, a fact that later helped to ensure that only Apple computers or licensed clones (with the copyright-protected ROMs from Apple) could run Mac OS.

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

- "Classic" Mac OS, the system which shipped with the first Macintosh in 1984 and its descendants, culminating with Mac OS 9.
- The newer Mac OS X (where the X is 10 written as a Roman numeral). Mac OS X incorporates elements of OpenStep (thus also BSD Unix and Mach) and Mac OS 9. Its low-level BSD-based foundation, Darwin, is free software/open source software.

History of Mac OS

On January 24, 1984, Apple Computer, Inc. (now Apple Inc.) introduced the Apple Macintosh personal computer, with the Macintosh 128K model, which came bundled with the Mac OS operating system, then known as the System Software. The Macintosh is often credited with popularizing the graphical user interface. The Mac OS has been pre-installed on almost every Macintosh computer ever sold. The operating system is also sold separately at Apple retail stores, and online. The original Mac OS was partially based on the Lisa OS, previously released by Apple for the Lisa computer in 1983 and, as part of an agreement allowing Xerox to buy shares in Apple at a favourable rate, it also used concepts from the Xerox PARC Xerox Alto which Steve Jobs and several other Macintosh team members had previewed.

Early history


The Macintosh project started in early 1979 with Jef Raskin, who envisioned an easy-to-use, low-cost computer for the average consumer. In September 1979, Raskin was given permission to start hiring for the project and was, in particular, looking for an engineer that could put together a prototype. Bill Atkinson, a member of the Apple Lisa team, introduced him to Burrell Smith, a service technician who had been hired earlier that year.

In January 1981, Steve Jobs completely took over the Macintosh project. Jobs and a number of Apple engineers visited Xerox PARC in December 1979, three months after the Lisa and Macintosh projects had begun. After hearing about the pioneering GUI technology being developed at Xerox PARC from former Xerox employees like Raskin, Jobs negotiated a visit to see the Xerox Alto computer and Smalltalk development tools in exchange for Apple stock options. The final Lisa and Macintosh operating systems mostly used concepts from the Xerox Alto, but many elements of the graphical user interface were created by Apple including the menubar and pop-up menus. The click-and-drag concept was developed by Jef Raskin.

Unlike the IBM PC, which used 8 kB of system ROM for power-on self-test (POST) and basic input/output chores (BIOS), the Mac ROM was significantly larger (64 kB) and held key OS code. Much of the original Mac ROM was coded by Andy Hertzfeld, a member of the original Macintosh team. He was able to conserve some of the precious ROM space by interleaving some of the assembly language code. In addition to coding the ROM, he also coded the kernel, the Macintosh Toolbox and some of the desktop accessories (DAs) as well. The icons of the operating system, which represented folders and application software were designed by Susan Kare, who later designed the icons for Microsoft Windows 3.0. Bruce Horn and Steve Capps wrote the Macintosh Finder as well as a number of Macintosh system utilities.

Apple was very strong in advertising their newfound machine. After it was created, the company bought all 39 pages of advertisement space in the Newsweek magazine, 1984 November/December edition. Apple was so successful in its marketing for the Macintosh, that it quickly outshone its more sophisticated predecessor, the Lisa, in sales – so much so that Apple quickly developed a product called MacWorks which allowed the Lisa to emulate Macintosh system software through System 3, by which time it had been discontinued as the re-branded Macintosh XL. Many of Lisa's operating system advances would not appear in the Macintosh OS until System 7.


The first version of the Mac OS (simply called System) is easily distinguished between other operating systems from the same period because it does not use a command line interface; it was one of the first operating systems to use an entirely graphical user interface. Additional to the system kernel is the Finder, an application used for file management, which also displays the Desktop. The two files were contained in a folder directory labeled System Folder, which contained other resource files, like a printer driver, needed to interact with the System.

System 1, 2, 3 & 4

These releases could only run one application at a time, though special application shells such as Switcher (discussed under MultiFinder) could work around this to some extent. System 1.0, 1.1, and 2.0 used a flat file system with only one kludged level of folders, called Macintosh File System (MFS); its support for folders (subdirectories) was incomplete. System 2.0 added support for AppleTalk and the newly introduced LaserWriter to use it. System 2.1 (Finder 5.0) introduced the HFS (Hierarchical File System) which had real directories. This version was specifically to support the Hard Disk 20 and only implemented HFS in RAM, startup and most floppy disks remained MFS 400K volumes. System 3.0 was introduced with the Mac Plus, officially implementing HFS and 800K startup drives and adding support for several new technologies including SCSI and AppleShare and introducing Trash "bulging" (i.e., when the Trash contained files, it would gain a bulged appearance). System 4.0 came with the Mac SE and Macintosh II, which required additional support for the first expansion slots, the Apple Desktop Bus (ADB), internal hard drives and on the Mac II, color, larger displays and the first Motorola 68020 processor.

Changes in early Macintosh operating systems are best reflected in the version number of the Finder, where major leaps are found between 1.x, 4.x, 5.x, and 6.x.

Original 1984 Mac OS desktop

System Software Release
System Version
Release Date
Finder Version
LaserWriter Version
Release Information
Mac System Software
1.0 (.97)
January 24, 1984
Initial Release
Mac System Software (0.1)
May 5, 1984
Maintenance Release, Added Mountain scene, About box, Clean Up Command
Mac System Software (0.3 & 0.5)
April 1985
Finder Update
System software
September 1985
Release for Hard Disk 20 support
Mac System Software (0.7)
January 1986
Introduced with Mac Plus
System Software 1.0
February 1986
System Software 1.1
February 1986
Fixed problems with data loss, system crashes; updated Chooser and Calculator
System Software 2.0
January 1987
Release for Macintosh II and SE
System software
Release for Macintosh 512Ke AppleShare 2.0 support
System Software 2.01
March 1987
Introduced AppleShare
System Software 2.01
April 1987
Maintenance Release of System Software. Updated LaserWriter Driver

System Software 5

System Software 5 (also referred to as simply System 5) added MultiFinder, an extension which let the system run several programs at once. The system used a co-operative multitasking model, meaning that time was given to the background applications only when the running application yielded control. A clever change in system functions that applications were already calling to handle events made many existing applications share time automatically. Users could also choose to not use MultiFinder, and thus stick with using a single application at a time as in previous releases of the system software.

System Software 5 was also the first Macintosh operating system to be given a unified "Macintosh System Software" version number, as opposed to the numbers used for the System and Finder files.

System Software 5 was available for a very short time and only in some countries, including the United States.

System Software Release
System Version
Release Date
Finder Version
Multi Finder Version
Laser Writer Version
Release Information
1987 circa
Initial Release
1988 circa
Updated LaserWriter Driver and new version of Apple HD SC Setup

System Software 6

System Software 6 (also referred to as simply System 6) was a consolidation release of the Mac OS, producing a complete, stable, and long-lasting operating system. Two major hardware introductions requiring additional support under System 6 were the 68030 processor and 1.44MB SuperDrive debuting with the Macintosh IIx and Macintosh SE/30. Later it would include support for the first specialized laptop features with the introduction of the Macintosh Portable. From System 6 forward, the Finder would have a unified version number closely matching that of the System, alleviating much of the confusion caused by the often considerable differences between earlier Systems.

System Version
Release Date
Finder Version
Multi Finder Version
Laser Writer Version
Release Information
April, 1988
Initial Release
September 19,
Release for Macintosh IIx (1988)
Late 1988
Maintenance Release
March 7, 1989
Release for Macintosh IIcx (1989)
September 20, 1989
Release for Macintosh IIfx (1990)
March 19, 1990
Not released because of AppleTalk bug
October 15, 1990
Initial Release
October 16, 1990
Official release for Macintosh LC, IIsi and Classic (1990)
April, 1991
Updated printing software to match software of System 7.0
Late 1991/Early 1992
Limited maintenance release for Pacific customers

System 7

On May 13, 1991 System 7 was released. It was the second major upgrade to the Mac OS, adding a significant user interface overhaul, new applications, stability improvements and many new features. Its introduction coincided with the release of and provided support for the 68040 Macintosh line.

Screenshot of System 7.5.3 Revision 2 image
Screenshot of System 7.5.3 Revision 2

Perhaps the most significant feature of System 7 was page swapping support, which previously had only been available as a third-party add-on. Accompanying this was a move to 32-bit memory addressing, necessary for the ever-increasing amounts of RAM available to the Motorola 68030 CPU. Earlier versions of Mac OS had used the lower 24 bits for addressing, and the upper 8 bits for flags. This had been an effective solution for earlier Macintosh models with very limited amounts of RAM, but it became a liability later. Apple described code that assumed the 24 + 8-bit addressing as being "not 32-bit clean", and most such applications would crash when 32-bit addressing was enabled by the user. The original Macs used the Motorola 68000 CPU which could address only 16 MB of memory. 24 Bits is all that is needed to address the 16MB memory space. This was a hardware limitation, not a system software design fault. The 68020/68030/68040 CPUs have 32-bit address buses and can address up to 4 GB of physical memory. As Apple moved to the 68030 CPU it needed to allow the use of more than 16 MB of memory. Thus the transition to 32-bit clean ROMs and software had to be implemented.

One notable System 7 feature was the built-in co-operative multitasking. In System Software 6, this function was optional through the MultiFinder. System 7 also introduced aliases, similar to shortcuts that were introduced in later versions of Microsoft Windows. System extensions were enhanced, by being moved to their own subfolder; a subfolder in the System Folder was also created for the control panels. In System 7.5, Apple included the Extensions Manager, a previously third-party program which simplified the process of enabling and disabling extensions.

The Apple menu, home only to desk accessories in System 6, was made more general-purpose: the user could now make often-used folders and applications—or anything else they desired—appear in the menu by placing aliases to them in an "Apple Menu Items" subfolder of the System Folder. AppleScript, a scripting language for automating tasks, was also introduced with System 7. 32-bit QuickDraw, supporting so-called "true color" imaging, was also included as standard; it was previously available as a system extension. TrueType, an outline font standard, was also introduced with System 7.

The Trash, under System 6 and earlier, would empty itself automatically when shutting down the computer or, if MultiFinder were not running, when launching an application. System 7 reimplemented the Trash as a special hidden folder, allowing files to remain in it across reboots until the user deliberately chose the "Empty Trash" command.

System 7.1 was mainly a bugfix release, with a few minor features added. System 7.1 was not only the first operating system to cost money (all previous versions were free or sold at the cost of the floppies), but also received a "Pro" sibling with extra features. System 7.1.2 was the first version to support PowerPC-based Macs. System 7.1 also introduced the System Enablers as a method to support new models without updating the actual System file. This led to extra files inside the system folder (one per new model supported) that some users found unpleasing.

System 7.5 introduced a large number of "high level" additions, considered by some to be less well thought-out than they could have been. Many of the new features were based on shareware applications that Apple bought and included into the new system. On the newer PowerPC machines, System 7.5 was plagued by stability problems due partly to a new memory manager (which can be turned off), and poor OS handling of errors in PowerPC code (all PowerPC exceptions map to Type 11). These growing pains did not afflict the 68k-architecture machines.

Mac OS 7.6

Stability improved in PPC Macs with Mac OS 7.6, which dropped the "System" moniker as a more-trademarkable name was needed in order to license the OS to the growing market of third-party Macintosh clone manufacturers. Mac OS 7.6 required a 68030 CPU and 32 bit clean ROMs, and so dropped support for many of the early Macs, including the Mac Plus and Mac II. Mac OS 7.6.1 finally introduced proper error handling for PowerPC code, so that errors in PowerPC code did not always force an immediate reboot.

Mac OS 7.6.1 performing various tasks image
Mac OS 7.6.1 performing various tasks

Although the version number was subsequently changed to 8.x and 9.x, the internal core of the OS (except the nanokernel, which was replaced by a new one that support Multiprocessing Services 2.x in Mac OS 8.6) remained basically the same.

Version history

- System 7.0 (released in late 1991; integrated MultiFinder always enabled)
- System 7.0.1 (introduced with LC II and Quadra series)
- System 7 Tuner (update for both 7.0 and 7.0.1)
- System 7.1
- System 7.1 Pro (version 7.1.1, combined with PowerTalk, Speech Manager & Macintalk, Thread Manager)
- System 7.1.2 (first version for Macs equipped with a PowerPC processor)
- System 7.1.2P (only for Performa/LC/Quadra 630 series, very quickly replaced by 7.5)
- System 7.5
- System 7.5.1 (System 7.5 Update 1.0 — the first Macintosh operating system to call itself "Mac OS")
- System 7.5.2 (first version for Power Macs that use PCI expansion cards, usable only on these Power Macs and PowerBooks 5300 and Duo 2300)
- System 7.5.3 (System 7.5 Update 2.0)
- System 7.5.3L (only for Mac clones)
- System 7.5.3 Revision 2
- System 7.5.3 Revision 2.1 (only for Performa 6400/180 and 6400/200)
- System 7.5.4, released very briefly and withdrawn within hours. Replaced by 7.5.5
- System 7.5.5 Last to support non-32 bit clean Macs, including all with less than a 68030 CPU.
- Mac OS 7.6 (name formally changed because of the experimental clone program, although System 7.5.1 and later used the "Mac OS" name on the splash screen)
- Mac OS 7.6.1 Proper PowerPC error handling introduced.

Performas used to have their own, exclusive operating system before they were merged into System 7.5.

- System 7.0.1P
- System 7.1P
- System 7.1P1
- System 7.1P2
- System 7.1P3 (last release with new features)
- System 7.1P4
- System 7.1P5
- System 7.1P6

Mac OS 8

Mac OS 8 was released on July 26, 1997, shortly after Steve Jobs returned to the company. It was mainly released to keep the Mac OS moving forward during a difficult time for Apple. Initially planned as Mac OS 7.7, it was renumbered "8" to exploit a legal loophole to accomplish Jobs's goal of terminating third-party manufacturers' licenses to System 7 and shutting down the Macintosh clone market. 8.0 added a number of features from the stillborn Copland project, while leaving the underlying operating system unchanged. A multi-threaded Finder was included, enabling better multi-tasking. The GUI was changed in appearance to a new shaded greyscale look called Platinum, and the ability to change the appearance themes (also known as skins) was added with a new control panel. This capability was provided by a new "appearance" API layer within the OS, one of the few significant changes.

Mac OS 8.1 desktop image
Mac OS 8.1 desktop

Apple sold 1.2 million copies of Mac OS 8 in its first two weeks of availability and 3 million within six months. In light of Apple's financial difficulties at the time, there was a large grassroots movement among Mac users to upgrade and 'help save Apple'. Even some pirate groups refused to redistribute the OS.

Mac OS 8.1 saw the introduction of an updated version of the Hierarchical File System called HFS Plus, which fixed many of the limitations of the earlier system (HFS Plus continues to be used in Mac OS X). There were some other interface changes such as separating network features from printing (the venerable, and rather odd Chooser was at last headed for retirement), and some improvements to application switching. However, in underlying technical respects, Mac OS 8 was not very different from System 7.

Mac OS 8.5 focused on speed and stability, with lots of old 68k code replaced by modern code native to the PowerPC. It also improved the appearance on the system, although the theming feature was cut late in development.

- Mac OS 8.0 (first version to require a 68040 processor, dropping support for the remainder of the Macintosh II series and other 68030 Macs)
- Mac OS 8.1 (last version to run on a 68K processor, added support for USB on the Bondi iMac, added support for HFS+)
- Mac OS 8.5 (first version to run only on a PowerPC processor, added built-in support for Firewire on the PowerMac G3)
- Mac OS 8.5.1
- Mac OS 8.6 (included a new nanokernel for improved performance and Multiprocessing Services 2.0 support, added support for the PowerPC G4 processor)

Mac OS 9

Mac OS 9 was released on October 23, 1999. It was generally a steady evolution from Mac OS 8. Early development releases of Mac OS 9 were numbered 8.7. Mac OS 9 added improved support for AirPort wireless networking. It introduced an early implementation of multi-user support (though not considered a true multi-user operating system by modern standards). An improved Sherlock search engine added several new search plug-ins. Mac OS 9 also provided a much improved memory implementation and management. AppleScript was improved to allow TCP/IP and networking control. Mac OS 9 also made the first use of the centralized Apple Software Update to find and install OS and hardware updates. Other new features included its on-the-fly file encryption software with code signing and Keychain technologies, Remote Networking and File Server packages and much improved list of USB drivers.

Mac OS 9 also added some transitional technologies to help application developers adopt some Mac OS X features before the introduction of the new OS to the public, again easing the transition. These included new APIs for the file system, and the bundling of the Carbon library that apps could link against instead of the traditional API libraries — apps that were adapted to do this can be run natively on Mac OS X as well. Other changes were made in Mac OS 9 to allow it to be booted in the "classic environment" within Mac OS X. This is a compatibility layer in Mac OS X (in fact a Mac OS X application, originally codenamed the "blue box") that runs a complete Mac OS 9 operating system, so allowing applications that have not been ported to Carbon to run on Mac OS X. This is reasonably seamless, though "classic" applications retain their original Mac OS 8/9 appearance and do not gain the Mac OS X "Aqua" appearance.

- Mac OS 9.0
- Mac OS 9.0.2
- Mac OS 9.0.3
- Mac OS 9.0.4
- Mac OS 9.1
- Mac OS 9.2
- Mac OS 9.2.1
- Mac OS 9.2.2

Mac OS X

Mac OS X (pronounced /mæk oʊ ɛs tɛn/) is the line of graphical operating systems developed, marketed, and sold by Apple Inc. which succeeded the original Mac OS, which had been Apple's primary operating system since 1984. Unlike the earlier Macintosh operating system, Mac OS X is a Unix-based operating system[9] built on technology developed at NeXT from the second half of the 1980s until early 1997, when Apple purchased the company.[10]

The first version was Mac OS X Server 1.0 in 1999, which retained the earlier Mac operating system's "platinum" appearance and even resembled OPENSTEP in places. The desktop-oriented version, Mac OS X v10.0, followed in March 2001 sporting the new Aqua user interface. Since then, five more distinct "end-user" and "server" versions have been released, most recently Mac OS X v10.5 in October 2007. Releases of Mac OS X are named after big cats; for example, Apple calls Mac OS X v10.5 "Leopard," while its previous release was called "Tiger."

Versions of Mac OS X:

- Mac OS X v10.0 (Cheetah)
- Mac OS X v10.1 (Puma)
- Mac OS X v10.2 (Jaguar)
- Mac OS X v10.3 (Panther)
- Mac OS X v10.4 (Tiger)
- Mac OS X v10.5 (Leopard)
- Mac OS X v10.6 (Snow Leopard)


Mac OS Timeline image
Click image to view full version

Star Trek

One interesting historical aspect of the classic Mac OS was a relatively unknown secret prototype Apple started work on in 1992, code-named "Star Trek" (as in "to boldly go"). The goal of this project was to create a version of Mac OS that would run on Intel-compatible x86 personal computers. The project was instigated by Novell, Inc., who were looking to integrate their DR-DOS with the Mac OS UI as a retort to Microsoft's Windows 3.0. The Apple/Novell team (fourteen engineers from the former, four from the latter) was able to get the Macintosh Finder and some basic applications, like QuickTime, running smoothly on a PC. Some of the code from this effort was reused when porting the Mac OS later to PowerPC.

The project was short lived, being canceled only one year later in early 1993. There are two theories for the cancellation: the first is that Apple's board deep-sixed further development upon realising that going with Star Trek would mean an entirely new business model and one that would likely see a notable drop in Apple's lucrative hardware sales; and the second is that an x86 Mac OS was not commercially viable in the early nineties because Microsoft's contracts for Windows 3.1 forced PC manufacturers to pay a royalty to Microsoft for every computer shipped, regardless of what operating system it contained.

A further complication was that Star Trek was designed to be source-level compatible, not binary compatible, with the Mac OS. Mac applications would therefore have to be recompiled or rewritten by their developers to run on the x86 architecture, and there was much skepticism as to exactly how much work this would entail.

Fifteen years after Star Trek, support for the x86 architecture was officially included in Mac OS, and then Apple transitioned all desktop computers to the x86 architecture. This was not the direct result of earlier Project Star Trek efforts. The Darwin underpinning used for Mac OS X 10.0 and later included support for the x86 architecture. The remaining non-Darwin portion of Mac OS X (based on OPENSTEP, which ran on Intel processors) was released officially with the introduction of x86 Macintosh computers.

68000 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 exclusively used 100% reverse engineered code without the use of Apple technology. It ran extremely fast 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 68000 classic Mac applications to x86 platforms; development ceased in 2002 and the project is now defunct.

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

Unfortunately most of the Mac user base had already started moving to the PowerPC platform that offered excellent classic Mac 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 68000 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 68000-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 project even years later despite the availability of 7th & 8th generation x86 processors employing similar architecture paradigms present in the PowerPC. Many application developers were also creating and releasing both 68000 Classic 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. Soon Apple was no longer selling 68000-based Macs and the existing installed base started to quickly evaporate. Despite the eventual excellent 68000-emulation technology available they proved never to be even a minor threat to real Macs due to their late arrival and immaturity even several years after the release of much more compelling PowerPC based Macs.

The PearPC emulator is capable of emulating the PowerPC processors required by newer versions of the Mac OS (like Mac OS X). Unfortunately, it is still in the early stages and, like many emulators, tends to run much slower than a native operating system would.

During the transition from PowerPC to Intel processors, Apple realized the need to incorporate a PowerPC emulator into Mac 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 with porting efforts beginning to get it to run on 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 only run 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

Several computer manufacturers over the years have made Macintosh clones capable of running Mac OS, 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, a manufacturing company in Miami, FL called Psystar Corporation, announced a $499 clone that comes with a barebones system that can run Mac OS X 10.5 Leopard. Threatened with legal battles, Psystar originally called the system OpenMac and have since changed it to Open Computer.


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. A/UX had most of its success in sales to the U.S. government, where UNIX was a requirement that Mac OS could not meet.

Information from Wikipedia is available under the terms of the GNU Free Documentation License

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