ISO 9660

From Freepedia

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.

DVDs may also use the ISO 9660 file system (although the UDF file system is far more commonly used).

Contents

Levels and restrictions

There are different levels to this standard.

Level 1 
File names are restricted to eight characters with a three-character extension, upper case letters, numbers and underscore; maximum depth of directories is eight.
Level 2 
File names may be up to 31 characters.
Level 3 
Files allowed to be fragmented (mainly to allow packet writing, or incremental CD recording).

All levels restrict names to upper case letters, digits and underscores ("_"). Some CD authoring 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. Many CD authoring applications attempt to work around this by truncating filenames automatically, but at the risk of breaking applications that rely on a specific file structure.

Disc images

ISO 9660 file system images (ISO images) are a common way to electronically transfer the contents of CD-ROMs. They often have the filename extension .iso and are commonly referred to as "ISOs". It should be noted an .iso file may be:

  1. A single ISO 9660 file system image
  2. A multi-track disc image with a table of contents

Extensions

There are common extensions to ISO 9660 to deal with the limitations. Rock Ridge supports the preservation of Unix/Linux permissions and longer ASCII-coded names; Joliet supports names stored in Unicode, thus allowing almost any character to be used, even from non-Latin 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 and Joliet Volume Access.

See also

External links

Retrieved from "http://en.freepedia.org/ISO_9660.html"


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