ISO 9660

ISO 9660
Name	ISO 9660
Introduced	1988
Developer	International Organization for Standardization; European Computer Manufacturers Association
Type	optical disc filesystem
Extended from	High Sierra Format
Extended to	Joliet (file system); Rock Ridge; Universal Disk Format

ISO 9660 ISO 9660 is a standardized filesystem for optical disc media used to ensure cross-platform interchange among computing systems. It defines a directory hierarchy, filename constraints, and metadata layout suitable for read-only media such as CD-ROM; it was developed to foster interoperability among vendors including IBM, Microsoft, Apple Inc., Sony, and Philips (company).

Overview

ISO 9660 specifies on-disc structures that allow systems like MS-DOS, Windows, Unix, macOS, Amiga, Atari ST, and VMS to read the same medium. The standard inherits concepts from the High Sierra Format and influenced later formats including Universal Disk Format and vendor extensions by Microsoft Corporation and Sun Microsystems. It defines logical block sizes, primary and supplementary volume descriptors, and a path table to support directory lookup by firmware and operating systems such as FreeBSD, NetBSD, OpenBSD, and Linux.

History and development

Work on the specification began in the mid-1980s to resolve incompatibilities among vendors including Sony Corporation, Philips (company), Panasonic Corporation, and major computer manufacturers like IBM and Microsoft. The High Sierra Group produced an initial proposal that led to the ISO committee drafting the international standard under the auspices of the International Organization for Standardization and the European Computer Manufacturers Association. The first edition was published in 1988 and later revisions harmonized with optical media advances driven by companies such as NEC Corporation and Toshiba Corporation. The standard’s evolution paralleled the rise of CD-ROM publishing by organizations like Encyclopaedia Britannica and software distribution by Adobe Systems and Sierra Entertainment.

Specification and structure

ISO 9660 defines a volume containing a sequence of 2048-byte logical blocks and describes structures including the system area, volume descriptors, path table, and directory records. Volume descriptors (primary, supplementary, and transition) provide metadata consumed by firmware and software from vendors such as Apple Computer and Microsoft Corporation. Filenames follow restrictive rules akin to legacy systems like MS-DOS, limiting character set and length; directory depth and path length limits affect distribution practices used by publishers like Oracle Corporation and Symantec Corporation. The path table accelerates directory lookups for implementations on platforms such as SCO Group UNIX and embedded systems from Siemens AG.

Extensions and variants

To overcome filename and attributes limitations, several extensions and variants emerged. Rock Ridge extensions, influenced by the Berkeley Software Distribution lineage and projects at University of California, Berkeley, add POSIX semantics for permissions and symbolic links used by NetBSD and FreeBSD. Joliet (file system), introduced by Microsoft Corporation, allows Unicode filenames and long names to support Windows 95 and later Windows releases. Other variants include vendor-specific metadata schemes implemented by companies like Apple Inc. with hybrid layouts for classic Mac OS resource forks, and the adoption of Universal Disk Format by organizations such as the DVD Forum and Blu-ray Disc Association for rewritable optical media.

Implementations and compatibility

Many operating systems include ISO 9660 readers: Linux distributions use kernel drivers and userspace tools like mkisofs from cdrtools and genisoimage; Windows supports ISO images natively in recent versions and via third-party tools by Nero AG and Roxio. Optical authoring applications from Roxio, Nero AG, Apple Inc., and open-source projects such as cdrkit produce ISO 9660 images with optional Rock Ridge or Joliet extensions. Firmware in optical drives and embedded players from Sony Corporation and Philips (company) recognizes primary volume descriptors for bootable media created with specifications like the El Torito bootable CD-ROM extension.

Limitations and criticisms

Critics cite ISO 9660’s restrictive filename conventions and directory depth limits as impediments for modern content distribution by companies like Google and Amazon (company), and for multimedia projects by Disney and Warner Bros. Entertainment. The read-only nature and limited metadata hinder use cases requiring permissions, large file support, or extended attributes relied upon by Red Hat and Canonical (company). Although extensions such as Rock Ridge and Joliet mitigate compatibility issues, the multiplicity of extensions complicates interoperability among implementations from vendors including Microsoft Corporation, Apple Inc., and various open-source projects. Furthermore, successive standards like Universal Disk Format and modern container formats adopted by organizations such as The Linux Foundation have supplanted ISO 9660 for many applications.

Category:File systems