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ISO 9660: Difference between revisions
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{{Filesystems}}
'''ISO 9660''' is the standard file system for CD-ROMs. It is also widely used
on DVD and BD media and may as well be present on USB sticks or hard disks.
Its specifications are available for free under the name '''ECMA-119'''.
== Overview and caveats ==
ISO 9660 is not a complex file system, but has a few quirks that are worth remembering. It seems that some operating systems also create non-compliant CDs, so beware! The main example of this is the character set that is available for file names. Strictly, filenames may only consist of uppercase letters A-Z, digits,
dots, and underscores. Further there is a semicolon which separates the visible file name from its version number suffix. Many operating systems also allow lower case letters and other characters. Linux's [[VFS]] displays lower case filenames to the user despite the CD contents actually containing upper case characters.
=== Sector size ===
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Since sectors 0x00-0x0F of the CD are reserved as System Area,
the Volume Descriptors can be found starting at sector 0x10 (16). The format of the volume descriptors is as follows:
{| {{wikitable}}
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|}
The most common Boot System Use specification is [[El-Torito|El Torito]].
It records at bytes 71 to 74 as little-endian 32-bit number the
block address of the El Torito Boot Catalog. This catalog lists the
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| 152 || 4 || Location of Optional Type-M Path Table || int32_MSB || LBA location of the optional path table. The path table pointed to contains only big-endian values. Zero means that no optional path table exists.
|-
| 156 || 34 || Directory entry for the root directory || - || Note that this is not an LBA address, it is the actual Directory Record, which contains a
|-
| 190 || 128 || Volume Set Identifier || strD || Identifier of the volume set of which this volume is a member.
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| 574 || 128 || Application Identifier || strA || Identifies how the data are recorded on this volume. For extended information, the first byte should be 0x5F, followed by the filename of a file in the root directory. If not specified, all bytes should be 0x20.
|-
| 702 ||
|-
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| 776 || 37 || Bibliographic File Identifier || strD || Filename of a file in the root directory that contains bibliographic information for this volume set. If not specified, all bytes should be 0x20.
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== Directories ==
At some point when reading from an ISO 9660 CD, you will need a directory record to locate a file, even if you generally use the path table to locate the directory initially. Unlike the path tables, there is only one version of each directory table, and multi byte numbers are in both-endian format. Every directory will start with 2 special entries: an empty string, describing the "." entry, and the string "\1" describing the ".." entry. A directory record is laid out as follows:
{| {{wikitable}}
!Offset
!Size
!Type
!Description
|-
| 0 || 1 || int8 || Length of Directory Record.
|-
| 1 || 1 || int8 || Extended Attribute Record length.
|-
| 2 || 8 || int32_LSB-MSB || Location of extent (LBA) in both-endian format.
|-
| 10 || 8 || int32_LSB_MSB || Data length (size of extent) in both-endian format.
|-
| 18 || 7 || see format below || Recording date and time
|-
| 25 || 1 ||
|-
| 26 || 1 || int8 || File unit size for files recorded in interleaved mode, zero otherwise.
|-
| 27 || 1 || int8 || Interleave gap size for files recorded in interleaved mode, zero otherwise.
|-
| 28 || 4 || int16_LSB-MSB || Volume sequence number - the volume that this extent is recorded on, in 16 bit both-endian format.
|-
| 32 || 1 || int8 || Length of file identifier (file name). This terminates with a ';' character followed by the file ID number in ASCII coded decimal ('1').
|-
| 33 || (variable) || strD || File identifier.
|-
| (variable) || 1 || -- || Padding field - zero if length of file identifier is
|-
| (variable) || (variable) || -- ||
System Use -
The remaining bytes up to the maximum record size of 255 may be used
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specific), Apple ISO 9660 Extensions, Amiga AS entries, or Arbitrary
Attribute Interchange Protocol (AAIP: Extended Attributes and ACLs).
A reader of SUSP entries shall simply ignore all entry types
which it does not expect.
Joliet was defined by Microsoft Inc. to allow for filenames with
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=== Articles ===
* [[El-Torito]], a standard for creating bootable CD-ROMs
* [[Mkisofs]], about ISO 9660 producing programs: mkisofs, genisoimage, xorriso
* [[Optical Drive]], an overview about how to operate optical drives and media
=== External links ===
* [http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-119.pdf ISO 9660 (ECMA-119) specification]
* [[wikipedia:ISO 9660|ISO 9960 on Wikipedia]]
* [
* [ftp://ftp.ymi.com/pub/rockridge/susp112.ps SUSP 1.12 (entries CE , PD , SP , ST , ER , ES)]
* [ftp://ftp.ymi.com/pub/rockridge/rrip112.ps Rock Ridge: RRIP 1.12 (SUSP entries PX , PN , SL , NM , CL , PL , RE , TF , SF , obsolete: RR)]
* [http://www.estamos.de/makecd/Rock_Ridge_Amiga_Specific Amiga SUSP entry AS]
* [
* [http://www.buildorbuy.org/pdf/joliet.pdf Joliet addon-on specifications]
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