AFF is an disk image file distributed under open-source license. AFF format was developed Simson Garfinkel. AFF4 is the latest version of the format.

AFF format uses two types of compression types: fast and optimal ZLIB method and slower yet more efficient LZMA algorithm. Disk image file compressed with either of these methods can be encrypted if needed. In case of large files, the algorithm offers option to split the archive into smaller parts that use AFD extension.