Universal Disk Format (UDF) is an open, vendor-neutral file system for computer data storage for a broad range of media.
[4] Normally, authoring software will master a UDF file system in a batch process and write it to optical media in a single pass.
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).
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.
A "maximum write" revision additionally records the highest UDF support level of all the implementations that has written to this image.
Not all drives fully implement version 1.5 or higher of the UDF, and some may therefore be unable to handle VAT builds.
These media can be erased entirely at any time, making the disc blank again, ready for writing a new UDF or other file system (e.g., ISO 9660 or CD Audio) to it.
However, sectors of -RW media may "wear out" after a while, meaning that their data becomes unreliable, through having been rewritten too often (typically after a few hundred rewrites, with CD-RW).
This build adds an extra Sparing Table in order to manage the defects that will eventually occur on parts of the disc that have been rewritten too many times.
[14] The UDF specifications[5] allow only one Character Set OSTA CS0, which can store any Unicode Code point excluding U+FEFF and U+FFFE.
[16] The reference algorithm neither checks for forbidden code points nor interprets surrogate pairs, so like NTFS the string may be malformed.
[19][20] Similarly, Windows XP Service Pack 2 (SP2) cannot read DVD-RW discs that use the UDF 2.00 sparing tables as a defect management system.
[21] This problem occurs if the UDF defect management system creates a sparing table that spans more than one sector on the DVD-RW disc.
A similar tool for Linux, udffsck, was under development by Vojtech Vladyka as an extension of fsck, and it was planned to be added to the udftools package.
[24] A tool for toggling the write protection flag, udftune, was under development by Johannes Truschnigg in 2023 but could not be merged into the main udftools package because its maintainer Pali Rohár has reportedly lost access to his GitHub account.