Universal disk format

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The Universal Disk Format ( UDF ) is a platform-independent file system developed and specified by the Optical Storage Technology Association (OSTA), mainly used for DVDs , which is increasingly replacing the older ISO-9660 format. UDF was standardized as ISO 13346 , which is also known under the name ECMA-167. In principle, however, UDF can be used sensibly for all RW and RO media, including hard drives , provided the operating system used supports UDF.

Compared to ISO 9660, UDF does away with some restrictions:

  • With UDF, file names can be up to 255 characters long, with a total of 64,000 possible characters. (For comparison: With ISO 9660 Level 1: up to 8 characters for the file name plus 3 for the file name extension; with ISO 9660 Level 2: up to 31 ISO characters; with Joliet : up to 64 Unicode characters.)
  • No limitation of the directory depth to eight levels; maximum path length: 1023 characters.
  • Support for 8- and 16-bit character sets.
  • Differentiation between upper and lower case in file names.
  • Storage of file attributes of different operating systems.
  • Extension of the possible size of the file system in the Tebibyte area; Abolition of the maximum file size of two gibibytes .
  • Optimizations for writing to DVD ± R / DVD-RW and DVD-RAM .


A compatibility of UDF media with ISO 9660 can be established by DVD MicroUDF with an ISO 9660 Level 3 layer; the resulting UDF / ISO bridge disc can then, depending on the driver, be identified as UDF or ISO medium. Thanks to the UDF / ISO bridge , an older operating system or device, such as Windows 95 or a common DVD player, is able to read the files it contains from the ISO9660 file system, while more modern operating systems or devices use the UDF file that is also included. Use file system. All newer Windows versions already support read access to UDF, but not in every version . Linux from Kernel 2.6, Mac OS Classic from 8.6 support UDF reading and writing at least up to UDF 1.50, Windows from Vista up to UDF 2.50. Linux can read UDF up to version 2.60, but UDF 2.50 is the maximum that mkudffs , the UDF component of all open source burning programs, can create. UDF file systems with versions higher than 2.01 cannot be written by the Linux UDF driver itself. For creating and burning UDF 2.5 and 2.6, the commercial Nero Linux 4 is the only option to date under Linux .

UDF CDs / DVDs / ISOs can e.g. B. with the burning programs Nero (Windows, Linux), Toast (Mac OS), or K3b (Linux). As a free alternative for Windows, ImgBurn or CDBurnerXP can also be used in addition to the built-in burn function .

The UDF format is also the preferred file system for packet writing . With packet writing it is possible to use a writable optical medium similar to a removable hard drive or a USB stick . Packet writing using UDF is currently supported by almost all operating systems, the most prominent exception being Windows XP , for which there are, however, numerous packet writing programs from third-party providers.

The recording function of Windows Vista formats CD-Rs / DVD-Rs as UDF, even without user intervention, sometimes even before the request to write a file to the data carrier has been given. The automatically created CDs / DVDs are incompatible with Windows 2000 and older operating systems.


The following versions of UDF have appeared over the years:

(October 24, 1995) for CD-ROM
(November 3, 1995) first additions for DVD
(August 30, 1996) Standard format of DVD-Video
(February 4, 1997) Standard format for rewritable data DVDs (DVD-RAM, DVD ± RW, but also CD-RW)
(April 3, 1998) Standard format for film recordings on DVD-RAM
(March 15, 2000) Bug fixes for 2.00
(April 30, 2003) for BD-RE
(March 1, 2005) for BD-R

UDF 1.0x is usually found together with ISO 9660 as a UDF / ISO bridge in order to achieve better compatibility with older operating systems and devices.

For use as a replacement for floppy disks, e.g. DVD-RAM or packet writing on CD-R (W) and DVD ± R (W), UDF is only suitable from version 1.50. However, UDF 1.50 is only used by modern operating systems (Windows from Windows 2000 read and from Windows Vista also writes, Mac OS from Mac OS 8.6 read and write, macOS from 10.4 UDF 2.0, from 10.5 also UDF 2.6; Linux from Kernel 2.4 read and from Kernel 2.6 also writes, but only supported up to UDF 2.01, UDF 2.60 read from Kernel 2.6).

Norms and standards

  • ISO / IEC 13346 (parts 1 to 5), based on ECMA-167.

See also

Programs that can create and / or modify the Universal Disk Format :


  • David A. Solomon, Mark E. Russinovich; Inside Microsoft Windows 2000 , Third Edition, Microsoft Press, 2000, ISBN 0-7356-1021-5 .

Web links