Macintosh original operating system OS

“Classic” Mac OS (1984-2001)

Original 1984 Mac OS desktop
Main article: Mac OS history

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 singletasking (in early versions) or cooperative multitasking (in later versions), very limited memory management, lack of protected memory, and susceptibility to conflicts among “extensions” that extend the operating system, providing additional functionality (such as networking) or support for a particular device. Some extensions may not work properly together, or work only when loaded in a particular order. Troubleshooting Mac OS extensions can be a time-consuming process of trial and error.

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

Most file systems used with DOS, Unix, or other operating systems treat a file as simply a sequence of bytes, requiring an application to know which bytes represented what type of information. By contrast, MFS and HFS gave files two different “forks”. The data fork contained the same sort of information as other file systems, such as the text of a document or the bitmaps of an image file. The resource fork contained other structured data such as menu definitions, graphics, sounds, or code segments. A file might consist only of resources with an empty data fork, or only a data fork with no resource fork. A text file could contain its text in the data fork and styling information in the resource fork, so that an application which didn’t recognize the styling information could still read the raw text. On the other hand, these forks provided a challenge to interoperability with other operating systems; copying a file from a Mac to a non-Mac system would strip it of its resource fork.

The Classic OS is still supported and Classic Applications Support is shipped in addition to OS X with PowerPC (but not Intel) Macs as late as early 2006.