ISO, UDF, and UDF/ISO

ISO (not an acronym)

Besides the standards organization, this in the CD world is a CD image format somewhat similar to a BIN/CUE image fileset, but the one single .ISO file contains both: the data and the CD layout information. These types of images can be burned with several CD burning programs.

ISO 9660

a standard CD-ROM file system that allows you to read the same CD-ROM whether you're on a PC, Mac, or other major computer platform. The standard, issued in 1988, was written by an industry group named High Sierra. Almost all computers with CD-ROM drives can read files from an ISO 9660 file system.
There are several specification levels. In Level 1, file names must be in the 8.3 format (no more than eight characters in the name, no more than three characters in the suffix) and in capital letters. Directory names can be no longer than eight characters. There can be no more than eight nested directory levels. Level 2 and 3 specifications allow file names up to 32 characters long.

Joliet, an extension to ISO 9660 from Microsoft, allows the use of Unicode characters in file names (needed for international user) and file names up to 64 characters in length.

UDF(Universal Disc Format)

One of the major achievements of DVD is that it has brought all the conceivable uses of CD for data, video, audio, or a mix of all three, within a single physical file structure called UDF, the Universal Disc Format. Promoted by the Optical Storage Technology Association (OSTA), the UDF file structure ensures that any file can be accessed by any drive, computer or consumer video. It also allows sensible interfacing with standard operating systems as it includes CD standard ISO 9660 compatibility. UDF overcomes the incompatibility problems from which CD suffered, when the standard had to be constantly rewritten each time a new application like multimedia, interactivity, or video emerged.

The version of UDF chosen for DVD-Video to suit both read-only and writable versions - is a subset of the UDF Revision 1.02 specification known as MicroUDF (M-UDF).

Because UDF wasn't supported by Windows until Microsoft shipped Windows 98, DVD providers were forced to use an interim format called UDF/ISO (UDF Bridge).

UDF has been revised and now appears in revisions 1.02, 1.5, and 2.0.


UDF/ISO

Also called UDF bridge, UDF/ISO is a hybrid filesystem utilizing UDF and ISO 9660. Developed because UDF wasn't supported by Windows until Microsoft shipped Windows 98, DVD providers were forced to use an interim format. Windows 95 OSR2 supports UDF Bridge, but earlier versions do not. As a result, to be compatible with Windows 95 versions previous to OSR2, DVD vendors had to provide UDF Bridge support along with their hardware.

DVD-ROM discs use the UDF Bridge format. (Note: Windows 95 was not designed to read UDF but can read ISO 9660). The UDF Bridge specification does not explicitly include the Joliet extensions for ISO 9660, which are needed for long filenames. Windows 98 and later MS operating systems read UDF so these systems have no problem with either UDF or long filenames. Burnworld