What is MacBinary, and how can I decode it?

Note: Because Mac OS X supports but no longer relies upon the forked file structure found in Mac OS 9 and earlier, the MacBinary format has largely been superseded by the disk image (.dmg) and GNU Zip (.zip) formats in OS X.

Because of the Mac OS forked file structure, transferring Mac OS files to non-Macintosh computers is problematic. MacBinary was developed as a means of preserving this structure without sacrificing portability. It combines the data and resource forks and the Finder information of a file into a single document. This document is then suitable for transport via FTP, the web, and email. You can also store the document on computers that run different operating systems, such as Unix or Windows. It is similar to BinHex, but MacBinary produces binary files as opposed to ASCII text. Thus, MacBinary files take up less disk space than BinHex files, but older applications and servers are more likely to corrupt them.

The first incarnation of MacBinary was released in 1985. It was later updated to MacBinary II, to accommodate changes in Mac OS. Changes introduced to the Finder in Mac OS 8.5 necessitated the release of MacBinary III.

Files encoded with MacBinary, regardless of the version, usually have .bin appended to the ends of their filenames. Although some applications can extract and decode the files themselves, many pass off these tasks to the operating system, which then invokes StuffIt Expander to handle the files. If your computer does not automatically convert the files, use StuffIt Expander to manually convert them. For more information, see In Mac OS and Mac OS X, how do I use StuffIt products to decode encoded files and expand compressed files? If you have Windows, use Aladdin Expander to decode MacBinary files, available from Smith Micro.

If you are having trouble decoding a MacBinary file and you know that the file isn't corrupt, upgrade to MacBinary III if there's a newer version of your application that supports it. MacBinary III is a simple application that will decode all MacBinary files regardless of version. It is available from many online Mac OS software archives. You should do this especially if you are using Mac OS 8.5 and higher. StuffIt Expander 5.0 and later are also compatible with MacBinary III. In most cases, programs based on the MacBinary II specifications can decode files encoded with MacBinary III, but will delete icon badges and custom routing information, features introduced in Mac OS 8.5.

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Last modified on May 13, 2009.

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