ISO/IEC 13490 (also known as
ECMA-168) is the successor to
ISO 9660 (level 3), intended to describe the
file system of a
CD-ROM
A CD-ROM (, compact disc read-only memory) is a type of read-only memory consisting of a pre-pressed optical compact disc that contains computer data storage, data computers can read, but not write or erase. Some CDs, called enhanced CDs, hold b ...
or
CD-R
CD-R (Compact disc-recordable) is a digital media, digital optical disc data storage device, storage format. A CD-R disc is a compact disc that can only be Write once read many, written once and read arbitrarily many times.
CD-R discs (CD-Rs) ...
.
ISO 13490 has several improvements over its predecessor. It fully addresses the filename,
POSIX
The Portable Operating System Interface (POSIX; ) is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems. POSIX defines application programming interfaces (APIs), along with comm ...
attribute, and multibyte character issues that were not handled by ISO 9660. It is also a more efficient format, permits incremental recording, and permits both the ISO 9660 format and ISO/IEC 13490 format to co-exist on the same media. It also specifies how to use multisession properly.
It is derived from the Frankfurt Group (formed in 1990 by many CD-ROM and CD-WO hardware and media manufacturers, CD-ROM data publishers, users of CD-ROMs, and major computer companies
) proposal and fully supports
orange book media.
Multiple session overview
ISO 13490 define a rule for operating systems as to how to read a multiple-
session ISO 9660 volume from a
CD-R
CD-R (Compact disc-recordable) is a digital media, digital optical disc data storage device, storage format. A CD-R disc is a compact disc that can only be Write once read many, written once and read arbitrarily many times.
CD-R discs (CD-Rs) ...
. Instead of looking for the volume descriptor at offset 32,768 (
sector number 16 on a CD) from the start of the disc (which would be the default behavior in ISO 9660), programs accessing the disc should start reading from the 16th sector in the first
track of the ''latest'' session. Sector numbers form a contiguous sequence starting at the first session, and continue over added sessions and their gaps.
Hence, if a CD mastering program wants to add a single file to a CD-R that has an ISO 9660 volume, it has to append a session containing at least an updated copy of the entire directory tree, plus the new file. The duplicated directory entries can still reference the data files in the previous session(s).
In a similar way, file data can be updated or even removed. Removal is, however, only virtual: the removed content does not appear any more in the directory shown to the user, but it is still physically present on the disc. It can therefore be recovered, and it takes up space (such that the CD will become full even though appearing to still have unused space).
Support
Though it was originally intended for multisession support only to apply to
Mode 2 Form 1 formatted discs, some CD writing software supported multisession writing to Mode 1 format discs. Since only some of the early disc drives supported multisession Mode 1 discs, in many cases the second and following sessions would become unreachable in some drives.
Some older CD writing software, such as
Nero Burning ROM
Nero Burning ROM, commonly called Nero, is an optical disc authoring program from Nero AG. The software is part of the Nero Multimedia Suite but is also available as a stand-alone product. It is used for burning and copying optical media such ...
, would not import previous session data from an inserted disc. It could thus only write a subsequent session to a disc on the same computer that had written all the previous sessions, and then only if the previous session data was saved before the writing software was closed down.
See also
*
Universal Disk Format (UDF) based on ISO/IEC 13346 (also known as
ECMA-167)
*
Write Once Read Many (WORM)
*
ISO/IEC JTC 1
ISO/IEC JTC 1, entitled "Information technology", is a joint technical committee (JTC) of the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC). Its purpose is to develop, maintain an ...
References
External links
ECMA-168
{{ISO standards
Disk file systems
#13490
Ecma standards