Thursday, June 5, 2008

Versions



The early Macintosh operating system initially consisted of two pieces of software, called "System" and "Finder", each with its own version number.[1] 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 (1984-2001)

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 and its cooperative multitasking, it was criticized for its very limited memory management, lack of protected memory, and susceptibility to conflicts among operating system "extensions" that provide 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.

The Macintosh originally used the Macintosh File System (MFS), a flat file system with only one level of folders. This was quickly replaced in 1985 by the Hierarchical File System (HFS), which had a true directory tree. Both file systems are otherwise compatible.

Extensions Manager under Mac OS 9

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.

Classic Application Support was shipped with Mac OS X with PowerPC (but not Intel) Macs until early 2006. However, Intel-based Macintoshes cannot run the Classic system or applications, nor can PowerPC models that have been upgraded to Mac OS 10.5 Leopard.

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