From GEAR Software Knowledgebase
Universal Disc Format. A file system developed by the Optical Storage Technology Association (OSTA).
The Universal Disk Format (UDF) is a format specification of a file system for storing files on optical media. It is an implementation of the ISO/IEC 13346 standard (also known as ECMA-167). It is considered to be a replacement of ISO 9660, and today is widely used for (re)writable optical media. UDF is developed and maintained by the Optical Storage Technology Association (OSTA).
DVD-Video media use UDF version 1.02. These discs contain a so-called UDF Bridge format, where both an ISO 9660 as well as a UDF 1.02 filesystem are present on the same disc, describing the same filesystem.
All standard formats for video recording on DVD-style media use some version of the UDF filesystem.
- Philips' DVD+VR format uses UDF 1.02 with an ISO 9660 bridge for DVD+R and DVD+RW.
- The DVD Forum's DVD-VR format uses UDF 2.00 for DVD-R, DVD-RW and DVD-RAM.
- Blu-ray and the DVD Forum's HD-DVD will be using UDF 2.50 or UDF 2.60.
When combined with packet writing technology, UDF has the advantage of allowing files to be added to and removed from a disc through the normal filesystem mechanisms. That is, the contents of a disc can be manipulated in the same way a hard disk, floppy disk, or USB flash drive might be. This even works for sequentially written media such as CD-R, although files that are deleted remain on the disc occupying space. In Windows the disc appears as a drive letter, while in Unix/Linux or Mac OS X it is mounted to a directory.