The Universal Disk Format (UDF) is a platform-independent file system developed by the Optical Storage Technology Association (OSTA) that is used primarily for DVDs and is supposed to replace the ISO 9660 format. It was itself standardized as ISO 13346 and is also known as ECMA-167.

 It is much less restrictive, compared to ISO 9660:
 

▪File names can be up to 255 characters long which can be chosen from a set of 64000 possible characters (compare: ISO 9660 level 1 allows 8 characters for the file name plus 3 for the extension; ISO 9660 level 2 allows up to 31 ISO characters, Joliet (only Windows/OS/2/Unix): up to 64 unicode characters).

▪No restrictions on the directory depth to 8 levels, maximum path length: 1,023 characters

▪Support for 8 and 16 bit character sets

▪Distinction between uppercase and lowercase in filenames

▪Stores the file attributes of various operating systems

▪Expansion of the potential size of the file system into the terabyte range, thus lifting the maximum size of 2 gigabytes

▪Optimizations for writing DVD-R/DVD-RW and DVD-RAM

Compatibility of UDF mediums to ISO 9660 can be achieved with DVD MicroUDF with a ISO 9660 level 3 layer; the resulting UDF/ISO bridge disc can the be identified as either a UDF or ISO medium depending on the installed drivers. This even enables Windows 95 to read a UDF disc. All newer Windows versions already support reading native UDF. Linux has already been supporting reading and writing UDF discs for many years.

 The UDF format additionaly offers support for packet writing. This makes it possible to use a recordable optical medium just like a removable hard drive or USB stick. UDF packet writing is currently supported by almost all operating systems; a prominent exception is Windows XP, for which additional software must be installed.

 Sometimes, OEM DVD-RAM drives are missing a UDF driver. If this is the case, a suitable UDF driver must be downloaded from the internet.

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