Universal Disk Format
| Developer(s) | ISO/ECMA/OSTA |
|---|---|
| Full name | Universal Disk Format |
| Introduced | 1995 |
| Limits | |
| Max. volume size | 2 TiB (hard disk), 8 TiB (optical disc) |
| Max. file size | 16 EiB |
| Max. filename length | 255 bytes (path 1023 bytes) |
| Allowed characters in filenames | Any Unicode except NUL |
| Features | |
| Dates recorded | creation, archive, modification (mtime), attribute modification (ctime), access (atime) |
| Date resolution | Microsecond |
| File system permissions | POSIX |
| Transparent compression | No |
| Other | |
| Supported operating systems | Various |
Universal Disk Format (UDF) is a profile of the specification known as ISO/IEC 13346 and ECMA-167 and is an open vendor-neutral file system for computer data storage for a broad range of media. In practice, it has been most widely used for DVDs and newer optical disc formats, supplanting ISO 9660. Due to its design, it is very well suited to incremental updates on both recordable and (re)writable optical media. UDF is developed and maintained by the Optical Storage Technology Association (OSTA).
Normally, authoring software will master a UDF file system in a batch process and write it to optical media in a single pass. But when packet writing to rewritable media, such as CD-RW, UDF allows files to be created, deleted and changed on-disc just as a general-purpose filesystem would on removable media like floppy disks and flash drives. This is also possible on write-once media, such as CD-R, but in that case the space occupied by the deleted files cannot be reclaimed (and instead becomes inaccessible).
Multi-session mastering is also possible in UDF, though some implementations may be unable to read disks with multiple sessions.
The Optical Storage Technology Association standardized the UDF file system to form a common file system for all optical media: both for read-only media and for re-writable optical media. When first standardized, the UDF file system aimed to replace ISO 9660, allowing support for both read-only and writable media. After the release of the first version of UDF, the DVD Consortium adopted it as the official file system for DVD-Video and DVD-Audio.
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