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Filename extension .bin
Internet media type application/macbinary
Uniform Type Identifier (UTI)

Due to the metadata-rich nature of the Macintosh Hierarchical File System, transferring Mac OS files to filesystems other than HFS can be problematic. MacBinary was developed as a means of preserving the Mac's dual-fork file 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 World Wide Web, and electronic mail. The documents can also be stored on computers that run operating systems with no HFS support, such as Unix or Windows.


Files encoded with MacBinary, regardless of the version, usually have a .bin or .macbin file extension appended to the ends of their filenames. E-mail programs such as Eudora can extract and decode MacBinary mail messages. Most dedicated FTP programs for the Mac, such as Fetch and Transmit, transparently decode MacBinary files they download.

MacBinary 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.

For Mac OS X, the MacBinary (and BinHex) format has been largely superseded by the tar.gz, ZIP archive and .dmg disk image format which is mounted as a volume after it has been double-clicked.


The first incarnation of MacBinary was released in 1985. The standard was originally specified by Dennis Brothers (author of the terminal program MacTEP and later an Apple employee), BinHex author Yves Lempereur, PackIt author Harry Chesley, et al. Lempereur then added support for MacBinary into BinHex 5.0, using MacBinary to combine the forks instead of his own methods. Most terminal programs and internet utilities added built-in MacBinary support during this period as well.

Two years later it was updated to MacBinary II, to accommodate changes in Mac OS. MacBinary II remained compatible with subsequent updates of the operating system for some time. This changed with the release of Mac OS 8, which necessitated the release of MacBinary III in 1996. In the meantime, Apple itself had released the AppleSingle and AppleDouble formats, which serve the same purpose as MacBinary, but correct some problems with it. The AppleSingle and AppleDouble formats were never widely adopted in the user community.


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