ISO 9660
ISO 9660 is a read-only filesystem often used on CD-ROMs. It is also common to encounter files containing an image of an ISO 9660 filesystem.
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Format details
The standard specifies a very limited filename format. At its strictest interchange level, it only allows DOS-style "8.3" names, uppercase only. At less strict levels, filenames can be up to 31 characters. Several extensions, mainly Rock Ridge and Joliet, were developed to mitigate these limitations.
The filenames also have a VMS-style version number, so sometimes they are shown with a ";1" suffix.
The size of a file is limited to 4GB (2GB in some implementations). This is irrelevant with respect to CD-ROMs, because of their small capacity, but it is a reason to avoid using ISO 9660 on DVD-ROMs and other media. (A feature called "multiple extents" makes larger files possible, but support for it may be limited.)
Identification
For the usual ISO 9660 image file format, the ASCII string "CD001" appears at offset 32769, and also 2048 bytes later at offset 34817.
The first 32768 bytes are not used. Be aware that hybrid filesystems are possible. Just because something is a valid ISO 9660 image, doesn't mean it can't also be a valid file of some other type.
Extensions
Some extensions to ISO 9660 are listed here.
See also: Wikipedia:Category:ISO 9660 extensions
SUSP
Main article: System Use Sharing Protocol
Rock Ridge
Main article: Rock Ridge
SUSP-based.
Joliet
Main article: Joliet
El Torito
Main article: El Torito
CD-ROM XA
Main article: CD-ROM XA
Apple extensions
Main article: Apple ISO 9660 extensions
Signature "AA" or "BA" in directory record system use area. "AA" is SUSP/Rock Ridge-like.
Amiga extensions
SUSP/Rock Ridge "AS" signature.
AAIP
Main article: AAIP
SUSP-based; "AL" signature.
zisofs extensions
Main article: zisofs
SUSP/Rock Ridge "ZF" signature.
Mkisofs transparent compression
Main article: mkisofs transparent compression
SUSP/Rock Ridge "ZZ" signature.
RISC OS extensions
Main article: ARCHIMEDES ISO 9660 extension.
Signature "ARCHIMEDES" in directory record system use area.
TRANS.TBL
Main article: TRANS.TBL
See also
- ISO image
- Universal Disk Format (UDF) - A successor to ISO 9660
- Hybrids of Apple Partition Map and ISO 9660 are common.
- See Disk Image Formats#Optical Disc Image Formats for formats that might contain this format.
Specifications
- ECMA-119
- ISO 9660:1988 (not free to download)
- OSDev Wiki: ISO 9660
Software
Reading
- 7-Zip, see here for an example
- isoinfo can perform basic operations and some validation.
- libcdio (
iso-info,iso-read, ...) - Operating systems often include drivers for ISO 9660. On Linux, an ISO 9660 image file can be mounted using a loopback driver (
mount -t iso9660 -o loop ...). - isolyzer is a tool that verifies if the file size of an ISO image is consistent with the information in its filesystem-level headers. This can be useful for detecting incomplete (e.g. truncated) ISO images. Apart from ISO 9660, isolyzer also supports UDF, HFS and HFS+, as well as hybrids of all of these filesystems.
Writing
- cdrkit → genisoimage
- Countless CD burning applications
