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HFS MACINTOSH FILE FORMATS

Macintosh files have two parts called the Data and Resource fork. Either may be empty. Unix (and many other OSs) can only cope with files having one part (or fork). To add to this, Macintosh files have a number of attributes associated with them - probably the most important are the TYPE and CREATOR. Again Unix has no concept of these types of attributes.

For example, a Macintosh file may be a JPEG image, where the image is stored in the data fork and a desktop thumbnail stored in the Resource fork. It is usually the information in the data fork that is useful across platforms.

Therefore to store a Macintosh file on a Unix file system, a way has to be found to cope with the two forks and the extra attributes (which are referred to as the finder info). Unfortunately, it seems that every software package that stores Macintosh files on Unix has chosen a completely different storage method.

The Apple/Unix formats that mkisofs (partially) supports are:

CAP AUFS format

Data fork stored in a file. Resource fork in subdirectory .resource with same filename as data fork. Finder info in .finderinfo subdirectory with same filename.

AppleDouble/Netatalk

Data fork stored in a file. Resource fork stored in a file with same name prefixed with "%". Finder info also stored in same "%" file. Netatalk uses the same format, but the resource fork/finderinfo is stored in subdirectory .AppleDouble with same name as data fork.

AppleSingle

Data structures similar to above, except both forks and finder info are stored in one file.

Helios EtherShare

Data fork stored in a file. Resource fork and finder info together in subdirectory .rsrc with same filename as data fork.

IPT UShare

Very similar to the EtherShare format, but the finder info is stored slightly differently.

MacBinary

Both forks and finder info stored in one file.

Apple PC Exchange

Used by Macintoshes to store Apple files on DOS (FAT) disks. Data fork stored in a file. Resource fork in subdirectory resource.frk (or RESOURCE.FRK). Finder info as one record in file finder.dat (or FINDER.DAT). Separate finder.dat for each data fork directory.

NOTE

mkisofs needs to know the native FAT cluster size of the disk that the PC Exchange files are on (or have been copied from). This size is given by the -cluster- size option. The cluster or allocation size can be found by using the DOS utility CHKDSK.

May not work with PC Exchange v2.2 or higher files (available with MacOS 8.1). DOS media containing PC Exchange files should be mounted as type msdos (not vfat) when using Linux.

SGI/XINET

Used by SGI machines when they mount HFS disks. Data fork stored in a file. Resource fork in subdirectory .HSResource with same name. Finder info as one record in file .HSancillary. Separate .HSancillary for each data fork directory.

Thursby Software Systems DAVE

Allows Macintoshes to store Apple files on SMB servers. Data fork stored in a file. Resource fork in subdirectory resource.frk. Uses the AppleDouble format to store resource fork.

Services for Macintosh

Format of files stored by NT Servers on NTFS file systems. Data fork is stored as "filename." Resource fork stored as a NTFS stream called "filename:AFP_Resource." The finder info is stored as a NTFS stream called "filename:Afp_AfpInfo". These streams are normally invisible to the user.

HFS Macinstosh File Names" section later.

When using the -apple option, the TYPE and CREATOR are stored in the optional System Use or SUSP field in the ISO9660 Directory Record in much the same way as the Rock Ridge attributes are. In fact, to make life easy, the Apple extensions are added at the beginning of the existing Rock Ridge attributes (i.e., to get the Apple extensions, you get the Rock Ridge extensions as well).

The Apple extensions require the resource fork to be stored as an ISO9660 associated file. This is just like any normal file stored in the ISO9660 file system except that the associated file flag is set in the Directory Record (bit 2). This file has the same name as the data fork (the file seen by non-Apple machines). Associated files are normally ignored by other OSs.

When using the -hfs option, the TYPE and CREATOR, plus other finder info, are stored in a separate HFS directory, not visible on the ISO9660 volume. The HFS directory references the same data and resource fork files described.

In most cases, it is better to use the -hfs option instead of the -apple option, as the latter imposes the limited ISO9660 characters allowed in filenames. However, the Apple extensions do give the advantage that the files are packed on the disk more efficiently, and it may be possible to fit more files on a CD, which is important when the total size of the source files is approaching 650MB.