ISO9660

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ISO9660 is a file system format that is used on many CDs. It is supported by TSK. See the ISO9660 Implementation Notes for ways that the file system was converted to the TSK layers.

ISO9660 Overview

This provides a quick introduction to the ISO9660 file system. The terms used are different then with other file systems. For a full overview of the file system, refer to the document "Volume and File Structure of CDROM for Information Interchange"

http://www.ecma-international.org/publications/standards/Ecma-119.htm

http://en.wikipedia.org/wiki/ISO_9660


Volume Descriptors

ISO9660 uses one or more Volume Descriptors to store information about the files on an ISO9660 volume. There will be a primary descriptor and other descriptors may exist that describe the files on the image differently (different file name restrictions, etc.). The volume descriptors define the block sizes, block counts, and point to other important file system structures.

Primary volume descriptors only allow uppercase filenames in the 8.3 format (8 chars dot 3 chars).

Supplementary volume descriptors are very similar to primary volume descriptors. The main difference is that supplementary volume descriptors can store file names in other encodings, such as Unicode and mixed case.

ISO9660 with "Joliet" support use the secondary volume descriptor to reference a duplicate directory tree that contains the Unicode names. ISO9660 with "Rock Ridge" adds additional metadata into the directory entries to store permissions and other metadata. These can exist in either the primary or secondary volume descriptor trees.

Metadata

File and directory metadata are stored in directory entries in the blocks allocated by the parent directory. Each entry has a dynamic length that is dependent on the length of the file name. Files are not assigned a numerical identifier. Instead, the file name is supposed to be the identifier in the directory. File content is located in contiguous blocks. The metadata points to the starting block and provides the number of bytes in the file.

File Names and Directories

The root directory is pointed to in the volume descriptor. From there, you can traverse the directory tree, like other file systems. ISO9660 also has a path table, which contains an entry for each directory. It will point you to the starting block for the directory. This allows you to jump to the directory faster (if the path table has been loaded).



Reference Documents

  • ECMA-119, The ECMA version of the ISO9660 standard. This is a formal spec that is not the easiest to read as an "Intro to ISO9660".
  • IEEE P1281: System Use Sharing Protocol, this defines how to use the System Use area of the ISO9660 spec. The System Use area is used by the Rock Ridge Extensions.
  • IEEE P1282: Rock Ridge Interchange Protocol, this defines how to use the System Use area to store long file names, POSIX info, sym links etc.
  • Joliet Specification, this defines the Joliet methods for storing longer file names and using Unicode in a "Secondary Volume Descriptor".