Mac OS is Apple Computer's operating system for Apple Macintosh computers. Mac OS was the first commercially successful operating system which used a graphical user interface. The Macintosh team included Bill Atkinson and Jef Raskin. 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.
The Mac OS can be divided into two families of operating systems:
An older and now unsupported "classic" Mac OS (the system that shipped with the first Mac in 1984 and its descendants, culminating with Mac OS 9).
The newer Mac OS X (pronunced oh-es-ten). 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 100% graphical operating system. Heralded for its ease of use, it is also criticized for its almost total lack of memory management, cooperative multitasking, and susceptibility to extension conflicts. "Extensions" are program modules that extend the operating system, providing additional functionality (such as a 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. The MacOS also introduced a new type of filesystem, which contained two different "forks" for a file. It was innovative at the time for separating out parameters into the resource fork, and raw data in the "data fork". However, it became quite a challenge to interoperate with other operating systems which did not recognize such a system.
The term "Mac OS" was not officially used until 1996 with the release of Mac OS 7.6 - prior to that the Macintosh operating system software was simply known as "The System", or by its version number, e.g. System 6 or System 7. Another common term was "the Toolbox". Apple deliberately played down the existence of the operating system in the early years of the Mac 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. With Mac, you turned it on, it just worked.
By the late 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.
Mac OS X
Mac OS X remedied this situation, bringing Unix-style memory management and preemptive multitasking. 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, although it is never seen unless a separate "terminal" program is launched. However, since these new features put higher demands on system resources, Mac OS X is only officially supported on G3 and newer processors. (It runs poorly on many early G3 machines). Mac OS X has a compatibility layer for running older Mac applications, but compatibility is not 100%.
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.