ISO

ISO 9660, a standard published by the International Organization for Standardization, defines a file system for CD-ROM media. It aims at supporting different computer operating systems such as Microsoft Windows, Mac OS, and systems that follow the UNIX specification, so that data may be exchanged.

The ISO 9660 file system is also used for DVD-ROMs.

Contents

Levels and restrictions

There are different levels to this standard.

Level 1 File names are restricted to 8 characters with a 3 character extension, upper case letters, numbers and underscore; maximum depth of directories is 8.
Level 2 File names may be up to 31 characters.
Level 3 Files allowed to be fragmented (used on CD-Rs written by the software "Direct CD" for Windows, for example).

All levels restrict names to upper case letters, digits and underscores ("_"). Some CD mastering applications allow the user to use almost any ASCII character. While this does not strictly conform to the ISO 9660 standard, most operating systems that can read ISO 9660 file systems support the use of most ASCII characters as an extension.

The restrictions on filename length and directory depth have been seen by many as a more serious limitation of the file system. While in many cases, it simply possible to rename file or truncate the filenames in question, and many CD burning applications do this automatically, in certain special cases, this is not feasible. For example, class files in Java are strictly required to follow naming rules, which especially in the case of nested classes may require filenames longer than 31 characters.

Disk images

Disk images of ISO 9660 file systems (ISO images) are a common way to electronically transfer the contents of CD-ROMs. They often have the extension .iso (though not necessarily), and are hence commonly referred to as "ISOs."

Extensions

There are common extensions to ISO 9660 to deal with the limitations. Rock Ridge supports the preservation of Unix permissions and longer ASCII coded names; Joliet supports names stored in Unicode, thus allowing almost any character to be used, even from non-roman scripts; El Torito enables CDs to be bootable.

ISO 13490 is basically ISO 9660 with multisession support.

Operating system support

Most operating systems support reading of ISO 9660 formatted discs, and most new versions support the extensions such as Rock Ridge and Joliet. Operating systems that do not support the extensions will usually show the basic (non-extended) features of a plain ISO 9660 disc.

Here are some operating systems and their support for ISO 9660 and extensions:

  • DOS: access with extensions, such as MSCDEX.EXE (Microsoft CDROM Extension) or CORELCD.EXE
  • Microsoft Windows 95, Windows 98, Windows ME: can read ISO 9660 Level 1, 2, 3, and Joliet
  • Microsoft Windows NT 4, Windows 2000, Windows XP: can read ISO 9660 Level 1, 2, 3, and Joliet
  • Linux and BSD: ISO 9660 Level 1, 2, 3, Joliet and Rock Ridge
  • Mac OS 7 to 9: ISO Level 1, 2. Optional free software supports Rock Ridge and Joliet: Joke Ridge (http://www.alex-castro.com/jokeridge/) and Joliet Volume Access (http://www.tempel.org/joliet/).
  • Mac OS X: probably the same as BSD.

See also:

External links

  • CD Recording FAQ (http://www.cdrfaq.org/)
  • Ecma-119 (http://www.ecma-international.org/publications/standards/Ecma-119.htm) - this standard is identical to ISO 9660.

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