Editing File Allocation Table (section)

=== <span id="ADS"></span>Forks and alternate data streams ===

The FAT file system itself is not designed for supporting [[fork (file system)|alternate data streams]] (ADS), but some operating systems that heavily depend on them have devised various methods for handling them on FAT volumes. Such methods either store the additional information in extra files and directories ([[classic Mac OS]] and [[macOS]]), or give new semantics to previously unused fields of the FAT on-disk data structures ([[OS/2]] and [[Windows NT]]).

Mac&nbsp;OS using [[PC Exchange]] stores its various dates, file attributes and long filenames in a [[hidden file]] called "<code>FINDER.DAT</code>", and [[resource fork]]s (a common Mac&nbsp;OS ADS) in a subdirectory called "<code>RESOURCE.FRK</code>", in every directory where they are used. From PC&nbsp;Exchange&nbsp;2.1 onwards, they store the Mac&nbsp;OS long filenames as standard FAT long filenames and convert FAT filenames longer than 31 characters to unique 31-character filenames, which can then be made visible to Macintosh applications.

[[macOS]] stores [[resource fork]]s and metadata (file attributes, other ADS) using [[AppleDouble format]] in a hidden file with a name constructed from the owner filename prefixed with "<code>._</code>", and [[Finder (software)|Finder]] stores some folder and file metadata in a hidden file called "<code>[[.DS_Store]]</code>" (but note that Finder uses <code>.DS_Store</code> even on macOS' native filesystem, [[HFS+]]).