ISO 9660

The rest begins with a volume descriptor set (a header block which describes the subsequent layout) and then the path tables, directories and files on the disc.

Other fields contain metadata such as the volume's name and creator, along with the size and number of logical blocks used by the file system.

Notable examples include Rock Ridge (Unix-style permissions and longer names), Joliet (Unicode, allowing non-Latin scripts to be used), El Torito (enables CDs to be bootable) and the Apple ISO 9660 Extensions (file characteristics specific to the classic Mac OS and macOS, such as resource forks, file backup date and more).

Called CD-ROMs, the lowest level format for these type of compact discs was defined in the Yellow Book specification in 1983.

In November 1985, representatives of computer hardware manufacturers gathered at the High Sierra Hotel and Casino (currently called the Golden Nugget Lake Tahoe) in Stateline, Nevada.

Present at the meeting were representatives from Apple Computer, AT&T,[citation needed] Digital Equipment Corporation (DEC), Hitachi, LaserData, Microware,[citation needed] Microsoft, 3M, Philips, Reference Technology Inc., Sony Corporation, TMS Inc., VideoTools (later Meridian[8]), Xebec, and Yelick.

[citation needed] The meeting report evolved from the Yellow Book CD-ROM standard, which was so open ended it was leading to diversification and creation of many incompatible data storage methods.

[5] JIS X 0606:1998 was passed in Japan in 1998 with much-relaxed file name rules using a new "enhanced volume descriptor" data structure.

Multi-byte values can be stored in three different formats: little-endian, big-endian, and in a concatenation of both types in what the specification calls "both-byte" order.

Both-byte order is required in several fields in the volume descriptors and directory records, while path tables can be either little-endian or big-endian.

[17] While it is suggested that they are reserved for use by bootable media,[18] a CD-ROM may contain an alternative file system descriptor in this area, and it is often used by hybrid CDs to offer classic Mac OS-specific and macOS-specific content.

These collectively act as a header for the data area, describing its content (similar to the BIOS parameter block used by FAT, HPFS and NTFS formatted disks).

[21] Since amendment 1 (or ECMA-119 3rd edition, or "JIS X 0606:1998 / ISO 9660:1999"), a much wider variety of file trees can be expressed by the EVD system.

The character set is no longer enforced, so both sides of the disc interchange need to agree via a different channel.

System Use Sharing Protocol (SUSP, IEEE P1281) provides a generic way of including additional properties for any directory entry reachable from the primary volume descriptor (PVD).

SUSP defines a method to subdivide that area into multiple system use fields, each identified by a two-character signature tag.

The idea behind SUSP was that it would enable any number of independent extensions to ISO 9660 to be created and included on a volume without conflicting.

The Rock Ridge Interchange Protocol (RRIP, IEEE P1282) is an extension which adds POSIX file system semantics.

[24] The standard takes its name from the fictional town Rock Ridge in Mel Brooks' film Blazing Saddles.

It was announced in November 1994[27] and first issued in January 1995 as a joint proposal by IBM and BIOS manufacturer Phoenix Technologies.

[30] El Torito can also be used to produce CDs which can boot up Linux operating systems, by including the GRUB bootloader on the CD and following the Multiboot Specification.

[29] While the El Torito spec alludes to a "Mac" platform ID, PowerPC-based Apple Macintosh computers don't use it.

These filenames are stored in a special supplementary volume descriptor, that is safely ignored by ISO 9660-compliant software, thus preserving backward compatibility.

Operating systems which can read Joliet media include: Romeo was developed by Adaptec and allows the use of long filenames up to 128 characters, written directly into the primary volume descriptor using the current code page.

[42] When a Windows installation of a different language opens a Romeo disk, the lack of code page indication will cause non-ASCII characters in file names to become Mojibake.

The same code page problem technically exists in standard ISO 9660, which allows open interpretation of the supplemental and enhanced volume descriptors to any character encoding subject to agreement.

Apple Computer authored a set of extensions that add ProDOS or HFS/HFS+ (the primary contemporary file systems for the classic Mac OS) properties to the filesystem.

Some of the additional metadata properties include:[43] In order to allow non-Macintosh systems to access Macintosh files on CD-ROMs, Apple chose to use an extension of the standard ISO 9660 format.

Operating systems that do not support the extensions usually show the basic (non-extended) features of a plain ISO 9660 disc.