ISO 9660
ISO 9660 is a standard of the International Organization for Standardization ( ISO), which describes a file system for optical media (CD- ROM, DVD- ROM, BD, etc.). The objective of this standard is to support several operating systems such as Microsoft Windows, Mac OS and UNIX systems so that data can be exchanged.
ISO 9660 is to be replaced by the Universal Disk Format.
- 3.1 Limited number of directories
Formation and properties
The standard was published in 1987, based on the High -Sierra file system two years earlier. It requires that file names can include up to eight characters and a three-letter file name extension in the lowest level of compatibility and can in this compatibility level to a maximum of eight directory levels. Multi- extent files are not allowed in the lowest level of compatibility, ie a file must be 4 gigabytes - 1 sector does not exceed. In a sector size of 2 kB file system size of 8 TB is possible. As a sign of the file name only uppercase letters, digits and the underscore are permitted in the lowest level of compatibility. All directories are listed alphabetically to produce. In the lowest level of compatibility files should not be fragmented stored on the disk. A CD- ROM that adheres to such strict guidelines can be read on almost any computer system.
The ISO 9660 standard is identical to the ECMA standard ECMA- 119th
Extensions
ISO 9660 Level 2
The standard ISO 9660 Level 2 (which is the next higher level of compatibility ) is less restrictive and allows file names up to a length of 31 characters.
ISO 9660 Level 3
Files may be fragmented, that is, are stored as so-called multi - extent files, mainly to allow files ≥ 4 GB as well as packet writing or incremental CD recording.
Joliet and Rock Ridge
The Joliet format is not an extension of the ISO 9660 standard, because that created by the company Microsoft Joliet is a separate file system, which is typically applied as a hybrid, whereas the Rock Ridge extensions expand the standard to Unix - specific file properties in the one provided in the ISO 9660 standard extension method to complement directory entries will be used. Since Joliet creates a separate file tree on the medium, it can be created in addition to Rockridge. Unlike Rock Ridge is in Joliet no connection between the file name in ISO -9660 - tree.
HFS combined with ISO 9660
Actually no extensions are required for older Mac OS versions, because the ISO 9660 standard, even in the lowest level of compatibility with the Associated Files already contains a direct mapping of the Apple resource forks. ISO 9660 was still often produced in combination with an HFS system. Both systems share while the file data, but each have their own metadata. Since HFS but has a limitation of 2 GB file size, HFS has been replaced lately by other extensions.
ISO 9660:1999
The current version of the ISO 9660 standards raises all artificial (ie not by the format itself related ) limitations.
File names can not contain in ISO 9660:1999 any characters, the maximum length of a path name component is increased to 207 octets (excluding XA extensions are even possible 221 octets ) and the restriction to 8 Directory hierarchy levels is lifted. In addition, the special meaning of the dot is lifted in file names.
Restrictions
Limited number of directories
ISO format has a limitation on the number of possible lists. Each ISO directory structure is based on a so-called "path table" (path table). This table provides an identification number to each folder. This number always refers to the parent folder to the root directory. So you allocate to each folder to the identification number of the parent folder. This identification number is a 16 -bit number, therefore the number of values is limited to 65536. As a result, the number of possible directories are limited depending on the structure (type of nesting). The maximum practical total number of directories does not specify, as only the number of parent root directories is limited to 65536. Since most operating systems, the "path table" not evaluate, the program offers mkisofs since July 2007, the use of-no -limit- pathtables to create a filesystem even if the limit is exceeded can.
Some operating systems - including Windows - going back to this path table, others - such as Linux - not use the table. On Windows, it may therefore be problems when a CD contains more than 65,536 directories. During the same CD in Linux is readable, are indeed able to see all files on the CD under Windows, but rendered as empty ( "zero length" ). Thus initially a flawless CD seems to have arisen, which proves to be faulty only when testing individual files.
Many CD writing programs such as Nero Burning ROM or Pinnacle Instant CD / DVD do not indicate this problem. Thus, it comes through the writing process to a seemingly flawless CD (under Windows) but this is not really useful.
ISO image
Main article: ISO Image
ISO 9660 file system images ( ISO images ) are a common way to distribute the content of CD -ROMs electronically. They usually have the file extension. Iso.