Universal Disk Format Guide, Meaning , Facts, Information and Description
For other less-common meanings of UDF, see UDF (disambiguation).The Universal Disk Format (UDF) is used for so called "packet-written" writable CD-ROMs. Packet writing allows CDs to be partially written using variable or fixed length records in multiple sessionss. Variable length packets written CD-Rs and CD-RWs can usually be closed to ISO 9660 format just by writing a table of contents on the CD. A Fixed length packet formatted CD can not be closed to ISO 9660 format, but can be randomly written and overwritten. Fixed length formatting cuts CD capacity by about 20% relative to ISO 9660 or variable length formatting.
Older operating systems do not support UDF unless special drivers are loaded, for example Microsoft Windows before the late 1990s. On these systems, UDF-formatted media can not be read without closing the CD to ISO 9660 format. Once closed, the CD can not be edited any more.
For the basic user UDF allows a CD-RW to be used like a floppy disk.
More generally, UDF is a format specification of a file system for storing files on recordable media, mainly media with limited rewriting conditions, such as:
- magneto-optical
- DVD (including DVD-ROM, DVD-R and others)
- CD-R, CD-RW
- Flash media above the Microsoft FAT32 limit of 32 GB/disc
- Iomega REV discs
- CD-MRW discs
- DVD-RAM discs
UDF is practically the successor of ISO 9660, supporting larger files, larger disk and more information about individual files and folders. It includes support for special file properties, such as Apple's File Types, Resource Forks, and other OS-specific data.
UDF is fully compliant with the ISO 13346 standard.
UDF has been released in multiple revisions:
- Revision 2.50. Added the Metadata Partition facilitating metadata clustering and optional duplication of file system information.
- Revision 2.01. Added support for Real Time Files.
- Revision 2.00. Added support for Stream Files, Access Control lists, and Power Calibration.
- Revision 1.50. Added support for (virtual) rewritability on CD-R and CD-RW media by intoducing the VAT structure, as used in file systems such as the product DirectCD by Roxio.
- Revision 1.02. This format is used by DVD-Video disks.
- Revision: 1.0
A contradictory rumour says Mac OS X 10.3.2 mounts and reads (but does not write) UDF 1.50 on DVD-RAM discs erased via such commands as Linux's mkudffs --udfrev=0x0150 /dev/scd$n.
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