Joliet (file system)

Joliet is a filesystem commonly used to store information on CD-ROM computer discs. It is defined as an extension to the ISO 9660 standard. Joliet was specified and endorsed by Microsoft and has been supported by all versions of its Windows operating system since Windows 95 and Windows NT 4.0. Its primary focus is the relaxation of the filename restrictions inherent with full ISO 9660 compliance.

Joliet accomplishes this by supplying an additional set of filenames that are encoded in UCS-2BE. These filenames are stored in a special supplementary volume descriptor, that is safely ignored by ISO 9660-compliant software, thus preserving backward compatibility.

The specification only allows filenames to be up to 64 Unicode characters in length. However, the documentation for mkisofs states filenames up to 103 characters in length do not appear to cause problems. Microsoft has documented it "can use up to 110 characters."

Many current PC operating systems are able to read Joliet-formatted media, thus allowing exchange of files between those operating systems even if non-Roman characters are involved (such as Arabic, Japanese or Cyrillic), which was formerly not possible with plain ISO 9660-formatted media. Operating systems which can read Joliet media include:

Microsoft recommends the use of the Joliet extension for developers targeting Windows. It allows Unicode characters to be used for all text fields, which includes file names and the volume name. A "Secondary" volume descriptor with type 2 contains the same information as the Primary one (sector 16 offset 40 bytes), but in UCS-2BE in sector 17, offset 40 bytes. As a result of this, the volume name is limited to 16 characters.

The disktype program prints the Joliet Unicode volume name, if present.

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