Science Fair Project Encyclopedia
Mac OS, which stands for Macintosh Operating System, is Apple Computerís name for the first operating systems for Macintosh computers. The original Mac OS was the first commercially successful operating system which used a graphical user interface. The Macintosh team included Bill Atkinson, Jef Raskin and Andy Hertzfeld.
There are a variety of views on how the Macintosh was developed and where the underlying ideas originated. While the connection between the Macintosh and the Alto project at Xerox PARC has been established in the historical record, the earlier contributions of Ivan Sutherland's Sketchpad and Doug Engelbart's On-Line System are no less significant. See History of the GUI, and Apple v. Microsoft.
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 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.
The Macintosh operating system was initially called System, as in "System 6.0.7" or "System 7". Among software engineers it was also sometimes referred to as the Toolbox, which consisted of a collection of standardized routines which programs could call rather than accessing the computer hardware directly. This abstraction is what allowed Mac applications written for one generation of system to run on later generations: from the Mac Plus to the Mac II, to the PowerBook, to the Power Macintosh, for example. Terms such as "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 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 on system support, given that the early Macs had no hard disk. However, only one model of Mac was ever actually bootable using the ROM alone, the 1991 Mac Classic model.
System 7.5.1 was the first to include the Mac OS logo (a blue smiley face). Mac OS 7.6 (which debuted in 1996) was the first to be named Mac OS because of the appearance of Mac "clones", workalikes from other companies such as Power Computing and Motorola, and 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 Macintosh in 1984 and its descendants, culminating with Mac OS 9.
- 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.
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" 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.
Mac OS also introduced the Hierarchical File System, an innovative new type of filesystem. Whereas a file on DOS or Unix would simply be a sequence of bytes, 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 system; for example, copying a file from a Mac to DOS or Unix would strip it of its resource fork.
Mac OS X
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 second Mac OS to include a command line (the first is the now-discontinued A/UX, which supported classic Mac OS applications on top of a UNIX kernel), although it is never seen unless the user launches a "terminal" program.
However, 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 for many purposes. Interestingly, as of 2004, every update to Mac OS X since the original public beta has had the peculiar quality of being noticeably faster and more responsive than the version it replaced, the opposite trend of most operating systems. As noted by John Siracusa of Ars Technica: For over three years now, Mac OS X has gotten faster with every release ó and not just "faster in the experience of most end users", but faster on the same hardware. This trend is unheard of among contemporary desktop operating systems. 
Mac OS X has 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 Mac OS X, but a few criticized it as being more difficult and less user-friendly than the original Mac OS.
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
Project 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 Project Star Trek. The goal of this project was to create a version of Mac OS that would run on Intel-compatible x86 personal computers. It was short lived, being cancelled only one year later in 1993 due to political infighting, though its team was able to get the Macintosh Finder and some basic applications, like QuickTime, running smoothly on a PC.
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 x86 PCs. These emulators were restricted to emulating the 68000 line of processors, and as such couldn't run versions of the Mac OS newer than 8.1, which required PowerPC processors. Recently, the PearPC emulator has appeared, which 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 OS would.
It is worth noting that the kernel of Mac OS X, Darwin, while not a reincarnation of Star Trek, runs on both x86 and PowerPC architectures. This has lead to speculation that Mac OS X could be ported to the x86 platform, though Apple have never shown any hint that they may pursue this direction.
This was an operating system that seamlessly integrated the Mac OS look and feel with the power and flexibility of Unix. One could look at A/UX as an early version of Mac OS X however since it was before the advent of PPC and had to run on the Motorola 68K processor it was not very competitive for its time. A/UX had most of its success in the Federal market where Unix was a requirement and Mac OS 7 et al could not meet that requirement.
- Mac OS history
- Mac OS X history
- Mac OS X Server
- List of Macintosh software
- Operating system advocacy
- Comparison of operating systems
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