Universal Disk Format

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Universal Disk Format
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{{short description|Vendor-neutral file system, used in practice for DVDs and other optical discs}}

{{mono>Partition type#PID 07h}} (Master boot record>MBR){{monoBasic Data Partition>EBD0A0A2-B9E5-4433-87C0-68B6B72699C7}} (GPT)| file_struct = | bad_blocks_struct = | max_filename_size = 255 bytes (path 1023 bytesThis restriction might be lifted in newer versions.)| max_files_no = Tebibyte>TiB (with 512 byte sectors), 8 TiB (with 2 KiB sectors, like most optical discs), 16 TiB (with 4 KiB sectors)232 × block sizeHTTPS://SITES.GOOGLE.COM/SITE/UDFINTRO/ >TITLE=WENGUANG'S INTRODUCTION TO UNIVERSAL DISK FORMAT (UDF) AUTHOR= WEBSITE=GOOGLE SITES, 16 July 2014, Exbibyte>EiBUnicode Code point excluding Byte order mark>U+FEFF and U+FFFE| dates_recorded = creation, archive, modification (mtime), attribute modification (ctime), access (atime)| date_range = 1 January 1 – 31 December 9999| date_resolution =Microsecond | forks_streams = Yes| attributes = Various| file_system_permissions = POSIX| compression = No| directory_struct = | encryption = | OS = Various}}Universal Disk Format (UDF) is a profile of the specification known as ISO/IEC 13346 and ECMA-167ECMA-167 - Volume and File Structure for Write-Once and Rewritable Media using Non-Sequential Recording for Information Interchange 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.Multi-session mastering has always been part of the UDF specification. See [UDF 2.01/6.10.1], though earlier documents were not very clear that the anchor offsets are specified to be from the last session.


{{Optical disc authoring}}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.OSTA - UDF Specifications


Multiple revisions of UDF have been released:Wenguang's Introduction to Universal Disk Format (UDF) UDF Revisions are internally encoded as binary-coded decimals; Revision 2.60, for example, is represented as 0x0260{{rp|23}}. In addition to declaring its own revision, compatibility for each volume is defined by the minimum read and minimum write revisions, each signalling the requirements for these operations to be possible for every structure on this image. A "maximum write" revision additionally records the highest UDF support level of all the implementations that has written to this image.{{rp|34}} For example, a UDF 2.01 volume that does not use Stream Files (introduced in UDF 2.00) but uses VAT (UDF 1.50) created by a UDF 2.60-capable implementation may have the revision declared as 0x0201, the minimum read revision set to 0x0150, the minimum write to 0x0150, and the maximum write to 0x0260.


The UDF standard defines three file system variations, called "builds". These are:
  • Plain (Random Read/Write Access). This is the original format supported in all UDF revisions
  • Virtual Allocation Table a.k.a. VAT (Incremental Writing). Used specifically for writing to write-once media
  • Spared (Limited Random Write Access). Used specifically for writing to rewritable media

Plain build

Introduced in the first version of the standard, this format can be used on any type of disk that allows random read/write access, such as hard disks, DVD+RW and DVD-RAM media. Metadata (up to v2.50) and file data is addressed more or less directly. In writing to such a disk in this format, any physical block on the disk may be chosen for allocation of new or updated files.Since this is the basic format, practically any operating system or file system driver claiming support for UDF should be able to read this format.

VAT build

Write-once media such as DVD-R and CD-R have limitations when being written to, in that each physical block can only be written to once, and the writing must happen incrementally. Thus the plain build of UDF can only be written to CD-Rs by pre-mastering the data and then writing all data in one piece to the media, similar to the way an ISO 9660 file system gets written to CD media.To enable a CD-R to be used virtually like a hard disk, whereby the user can add and modify files on a CD-R at will (so-called "drive letter access" on Windows), OSTA added the VAT build to the UDF standard in its revision 1.5. The VAT is an additional structure on the disc that allows packet writing; that is, remapping physical blocks when files or other data on the disc are modified or deleted. For write-once media, the entire disc is virtualized, making the write-once nature transparent for the user; the disc can be treated the same way one would treat a rewritable disc.The write-once nature of CD-R or DVD-R media means that when a file is deleted on the disc, the file's data still remains on the disc. It does not appear in the directory any more, but it still occupies the original space where it was stored. Eventually, after using this scheme for some time, the disc will be full, as free space cannot be recovered by deleting files. Special tools can be used to access the previous state of the disc (the state before the delete occurred), making recovery possible.Not all drives fully implement version 1.5 or higher of the UDF, and some may therefore be unable to handle VAT builds.

Spared (RW) build

Rewriteable media such as DVD-RW and CD-RW have fewer limitations than DVD-R and CD-R media. Sectors can be rewritten at random (though in packets at a time). 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).The plain and VAT builds of the UDF format can be used on rewriteable media, with some limitations. If the plain build is used on a -RW media, file-system level modification of the data must not be allowed, as this would quickly wear out often-used sectors on the disc (such as those for directory and block allocation data), which would then go unnoticed and lead to data loss. To allow modification of files on the disc, rewriteable discs can be used like -R media using the VAT build. This ensures that all blocks get written only once (successively), ensuring that there are no blocks that get rewritten more often than others. This way, a RW disc can be erased and reused many times before it should become unreliable. However, it will eventually become unreliable with no easy way of detecting it. When using the VAT build, CD-RW/DVD-RW media effectively appears as CD-R or DVD+/-R media to the computer. However, the media may be erased again at any time.The spared build was added in revision 1.5 to address the particularities of rewriteable media. 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. This table keeps track of worn-out sectors and remaps them to working ones. UDF defect management does not apply to systems that already implement another form of defect management, such as Mount Rainier (MRW) for optical discs, or a disk controller for a hard drive.The tools and drives that do not fully support revision 1.5 of UDF will ignore the sparing table, which would lead them to read the outdated worn-out sectors, leading to retrieval of corrupted data.

Character set

The UDF specifications allow only one Character Set OSTA CS0, which can store any Unicode Code point excluding U+FEFF and U+FFFE. Additional character sets defined in ECMA-167 are not used.{{rp|at=7.2}}Since Errata DCN-5157, the range of code points was expanded to all code points from Unicode 4.0 (or any newer or older version), which includes Supplementary Multilingual Plane characters. DCN-5157 also recommends normalizing the strings to Normalization Form C.WEB, UDF 2.60 approved errata,weblink 22 April 2018, The OSTA CS0 character set stores a 16-bit Unicode string "compressed" into 8-bit or 16-bit units, preceded by a single-byte "compID" tag to indicate the compression type.{{rp|at=2.1.2, 6.4}} The 8-bit storage is functionally equivalent to ISO-8859-1, and the 16-bit storage is UTF-16 in big endian. The reference algorithm neither checks for forbidden code points nor interprets surrogate pairs. Due to DCN-5157, the "Unicode" string needs to be interpreted as UTF-16 to represent plane 1–16 code points such as Emoji.


Many DVD players do not support any UDF revision other than version 1.02. Discs created with a newer revision may still work in these players if the ISO 9660 bridge format is used. Even if an operating system claims to be able to read UDF 1.50, it still may only support the plain build and not necessarily either the VAT or Spared UDF builds.Mac OS X 10.4.5 claims to support Revision 1.50 (see man mount_udf), yet it can only mount disks of the plain build properly and provides no virtualization support at all. It cannot mount UDF disks with VAT, as seen with the Sony Mavica issue.WEB,weblink Sony Mavica UDF Compatibility Issue, 19 February 2012, Apple, 16 July 2014, yes,weblink" title="">weblink April 26, 2012, WEB,weblink Mac OS X UDF Compatibility Issues, 11 July 2012, Free(code):, 16 July 2014, Releases before 10.4.11 mount disks with Sparing Table but does not read its files correctly. Version 10.4.11 fixes this problem.WEB,weblink Intel Update, 14 November 2007, Apple, 16 July 2014, yes,weblink" title="">weblink March 28, 2010, WEB,weblink PowerPC Update, 14 November 2007, Apple, 16 July 2014, yes,weblink" title="">weblink May 31, 2010, 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.WEB,weblink Microsoft Windows UDF Read Troubleshooting,, This problem occurs if the UDF defect management system creates a sparing table that spans more than one sector on the DVD-RW disc. Windows XP SP2 can recognize that a DVD is using UDF, but Windows Explorer displays the contents of a DVD as an empty folder. A hotfix is available for thisWEB,weblink Windows XP UDF hotfix,, and is included in Service Pack 3.WEB,weblink MS Windows and UDF optical discs, {| class="wikitable sortable"|+ Table of operating systems
  • Unless otherwise noted, read and write support means that only the plain UDF build is supported, but not the VAT and spared build.
  • Support for "read" means that a UDF formatted disk can be mounted by the system. It enables the user to read files from the UDF volume using the same interface that is used to access files on other disks connected to the computer.
  • Support for "write" means that, in addition to reading files from a mounted UDF volume, data such as files can be modified, added, or deleted.
!! colspan="5" | UDF revision (read + write)! colspan="2" | Non-plain!! Operating system! 1.02! 1.50! 2.0x! 2.50! 2.60! VAT! Sparing Tables! NoteAIX (operating system)>AIX 5.2, 5.3, 6.1|| {{yes}}| {{yes}}| {{no}}| {{no}}||PUBLISHER=IBM, 25 September 2010, | AmigaOS 4.0| {{yes}}| {{yes}}||||||BeOS/magnussoft ZETA/Haiku (operating system)>Haiku| {{yes}}| {{yes}}| {{yes}}| {{yes}}| {{yes}}|||| eComStation/OS/2||| {{yes}}||||| Additional fee drivers on OS/2.| FreeBSD 5.0 and newread only}}read only}}FREEBSD 5.0-RELEASE RELEASE NOTES >URL=HTTPS://WWW.FREEBSD.ORG/RELEASES/5.0R/RELNOTES-I386.HTML#AEN1150, | {{no}}| {{no}}| {{no}}| {{no}}| {{yes}}|| Linux kernel 2.2| {{no}}| {{no}}| {{no}}| {{no}}| {{no}}| {{no}}| {{no}}|| Linux kernel 2.4| {{yes}}| {{yes}}| {{yes}}Linux version 2.3.17 - 2.4.5 supports only UDF revision up to 2.00, Linux version 2.4.6 and newer supports also UDF revision 2.01| {{no}}| {{no}}| {{yes}}| {{yes}}|| Linux kernel 2.6.0 - 2.6.25| {{yes}}| {{yes}}| {{yes}}| {{no}}| {{no}}| {{yes}}| {{yes}}| Kernel versions prior to 2.6.10 supported fewer media types.| Linux kernel 2.6.26 and newer| {{yes}}| {{yes}}| {{yes}}read only}}WEB
, Linux 3.13: fs/udf/udf_sb.h
, 2013-09-24
, 2014-01-29,
read only}}{{rp|10}}| {{yes}}| {{yes}}| Permission-related mounting options added in 2.6.30.WEB
, Linux 2.6.30 Changelog
, 2009-06-12
, 2015-09-13, Auto-detection of UDF file system on hard disk is supported since version 2.6.30. Auto-detection of UDF file system on disk images was fixed in 4.11.
Mac OS 8#Mac OS 8.1>Mac OS 8.1 - 8.5| {{yes}}| {{no}}| {{no}}| {{no}}| {{no}}| {{no}}| {{no}}|Mac OS 8#Mac OS 8.6>Mac OS 8.6, Mac OS 9| {{yes}}| {{yes}}| {{no}}| {{no}}| {{no}}| {{no}}| {{no}}|| Mac OS X 10.0 - 10.3| {{yes}}QUOTE=UDF 1.50 IS SUPPORTED. UDF 2.0 AND LATER IS NOT., | {{no}}| {{no}}| {{no}}| {{no}}| {{no}}|| Mac OS X 10.4| {{yes}}| {{yes}}| {{yes}}Roxio Toast>Toast 9+ HD Plugin| {{no}}Support via third party utility Toast 9+| {{no}}| {{yes}}Since version 10.4.11| Can create UDF 1.50 (plain build) volumes using the drutil utility.| Mac OS X 10.5 and newer| {{yes}}| {{yes}}| {{yes}}QUOTE=READING OF ALL UDF REVISIONS (1.02 - 2.60) ON BOTH BLOCK DEVICE (E.G. HARD DRIVES AND USB DRIVES) AND MOST OPTICAL MEDIA IS SUPPORTED. WRITING TO BLOCK DEVICES, DVD-RW AND DVD+RW IS SUPPORTED WITH THE FOLLOWING EXCEPTIONS: (1) CANNOT WRITE FINDER INFO, RESOURCE FORK, OR OTHER EXTENDED ATTRIBUTES IN UDF VOLUMES OF REVISION 1.02 AND 1.50; (2) CANNOT WRITE TO MIRRORED METADATA PARTITION., DISC RECORDING RELEASE NOTES FOR OS X V10.5 >URL=HTTPS://DEVELOPER.APPLE.COM/LIBRARY/CONTENT/RELEASENOTES/MUSICAUDIO/RN-DISCRECORDING/INDEX.HTML, This release note describes changes to the Disc Recording frameworks from OS X version 10.4. The Disc Recording content creation engine now supports writing UDF 2.0 discs in addition to UDF 1.02 and 1.5., read only}}MAC TECHNOLOGY OVERVIEW - KERNEL AND DEVICE DRIVERS LAYER >URL=HTTPS://DEVELOPER.APPLE.COM/LIBRARY/CONTENT/DOCUMENTATION/MACOSX/CONCEPTUAL/OSX_TECHNOLOGY_OVERVIEW/SYSTEMTECHNOLOGY/SYSTEMTECHNOLOGY.HTML, OS X supports reading UDF revisions 1.02 through 2.60 on both block devices and most optical media, and it supports writing to block devices and to DVD-RW and DVD+RW media using UDF 2.00 through 2.50 (except for mirrored metadata partitions in 2.50)., | {{yes}}| {{yes}}| To create, use newfs_udf utility.| NetBSD 4.0read only}}HTTPS://WWW.NETBSD.ORG/RELEASES/FORMAL-4/NETBSD-4.0.HTML >TITLE=ANNOUNCING NETBSD 4.0, Added UDF support for optical media and block devices, see mount_udf(8). Read-only for now., read only}}read only}}read only}}read only}}| {{yes}}| {{yes}}| Reading multi-session VAT, spared and metapartition variants from all CD, DVD and BD variants as well as HDD and Flash media.| NetBSD 5.0| {{yes}}| {{yes}}| {{yes}}| {{yes}}| {{yes}}| {{yes}}| {{yes}}PUBLISHER=NETBSD, Create new with newfs_udf.Limited writing on 2.50/2.60 (due to needing pre-allocated, fixed sized metadata partition).HTTP://NETBSD.GW.COM/CGI-BIN/MAN-CGI?MOUNT_UDF+8+NETBSD-5.0 >TITLE=NETBSD SYSTEM MANAGER'S MANUAL, 25 September 2010, | NetWare 5.1||||||||| NetWare 6||||||||| OpenBSD 3.8 - 3.9read only}}HTTPS://WWW.OPENBSD.ORG/38.HTML>TITLE=OPENBSD 3.8, | {{no}}| {{no}}| {{no}}| {{no}}| {{no}}| {{no}}|| OpenBSD 4.0 - 4.6read only}}read only}}HTTPS://WWW.OPENBSD.ORG/40.HTML >TITLE=OPENBSD 4.0, | {{no}}| {{no}}| {{no}}| {{yes}}| {{no}}| | OpenBSD 4.7read only}}read only}}read only}}read only}}HTTP://WWW.OPENBSD.ORG/47.HTML >TITLE=THE OPENBSD 4.7 RELEASE DATE= PUBLISHER=OPENBSD, 25 September 2010, read only}}| {{yes}}| {{yes}}| Solaris (operating system)>Solaris 7 11/99+| {{yes}}| {{yes}}||||||| Solaris 8/9/10| {{yes}}| {{yes}}||||||DOS, FreeDOS, Windows 3.11, Windows 95, Windows 95#Editions>Windows 95 OSR2+ and other DOS based OSISO9660 backward compatibility structure can be read.| Windows 98, Windows Meread only and only for CD/DVD optical disks}}MICROSOFT CORPORATION>TITLE=MICROSOFT WINDOWS 98 RESOURCE KITPUBLISHER=MICROSOFT PRESSPAGE=442URL=HTTPS://ARCHIVE.ORG/DETAILS/ISBN_9781572316447/PAGE/442QUOTE=WINDOWS 98 HAS A NEW READ-ONLY UNIVERSAL DISK FORMAT (UDF) SYSTEM, WHICH SUPPORTS READING MEDIA FORMATTED ACCORDING TO UDF SPECIFICATION 1.02., MICROSOFT CORPORATION>TITLE=MICROSOFT WINDOWS 98 RESOURCE KITPUBLISHER=MICROSOFT PRESSPAGE=1316URL=HTTPS://ARCHIVE.ORG/DETAILS/ISBN_9781572316447/PAGE/1316QUOTE=THE 32-BIT, PROTECTED-MODE UDF FILE SYSTEM IN WINDOWS 98 IS IMPLEMENTED ACCORDING TO REVISION 1.02 OF UNIVERSAL DISK FORMAT SPECIFICATION BY OPTICAL STORAGE TECHNOLOGY ASSOCIATION (OSTA). IT PROVIDES READ-ONLY ACCESS TO UDF-FORMATTED MEDIA, SUCH AS DVD DISCS. THE UDF FILE SYSTEM USES VCACHE AND IS DYNAMIC, REQUIRING NO CONFIGURATION OR STATIC ALLOCATION ON THE PART OF THE USER., HTTPS://WWW.MICROSOFT.COM/MSJ/1197/NT5DLL.ASPX>TITLE=A PROGRAMMER'S PERSPECTIVE ON NEW SYSTEM DLL FEATURES IN WINDOWS NT 5.0, PART I MATT PIETREK>DATE=NOVEMBER 1997ACCESSDATE=9 SEPTEMBER 2017, Windows NT 5.0 also adds UDF (Universal Disk Format). ... The UDF implementations shipping in both Windows 98 (UDF 1.02) and Windows NT 5.0 (UDF 1.50) are read-only., | {{no}}| {{no}}| {{no}}| {{no}}| {{no}}| {{no}}Drive Letter Access>DLA, InCD or Toshiba/Panasonic/Matsushita UDF 2.5 driver. Read and write support for removable disks and hard disks available with third party utilities such as SAI's WriteUDF!.| Windows 2000read only}}RUSSINOVICH>FIRST1=M. E.FIRST2=D. A.URL=HTTPS://BOOKS.GOOGLE.COM/BOOKS?ID=3XQBRAAACAAJYEAR=2000LOCATION=REDMOND, WASHINGTONCHAPTER=CHAPTER 12 - FILE SYSTEMSLAST2=SOLOMONTITLE=MICROSOFT WINDOWS INTERNALS, FOURTH EDITION: MICROSOFT WINDOWS SERVER 2003, WINDOWS XP, AND WINDOWS 2000EDITION=FOURTHPUBLISHER=MICROSOFT PRESSISBN=0-7356-1917-4CHAPTER=CHAPTER 12 - FILE SYSTEMSURL=HTTP://WWW.MICROSOFT.COM/WHDC/DEVICE/STORAGE/LOCFILESYS.MSPXTITLE=LOCAL FILE SYSTEMS FOR WINDOWSPAGES=6–8FORMAT=DOC, read only}}| {{no}}| {{no}}| {{no}}| {{no}}| {{no}}| Additional read/write support via third party utilitiesWindows XP/Windows Server 2003>Server 2003read only}}read only}}read only}}| {{no}}| {{no}}| {{yes}}| {{yes}}Service Pack 3 required| Additional read/write support via third party utilitiesWindows Vista/Windows 7>7/Windows 8/Windows 10>10LAST2=SOLOMONLAST3=IONESCUTITLE=WINDOWS INTERNALS, 5TH EDITION: WINDOWS VISTA AND WINDOWS SERVER 2008YEAR=2009LOCATION=REDMOND, WASHINGTON, 978-0-7356-3796-2chapter=Chapter 12 - File Systemsquote=The UDF driver supports UDF versions up to 2.60. The Windows UDF driver (Udfs.sys) provides read-write support ... when using UDF 2.50 and read-only support when using UDF 2.60. However, Windows does not implement support for certain UDF features such as named streams and access control lists., RUSSINOVICH >FIRST1=M. E.FIRST2=D. A., Ionescu title=Windows Internals, Part 2, 6th Edition: Windows 7 and Windows Server 2008 R2year=2012 location=Redmond, Washington, 978-0-7356-6587-3chapter=Chapter 12 - File Systems quote=The UDF driver supports UDF versions up to 2.60. The Windows UDF driver (Udfs.sys) provides read-write support ... when using UDF 2.50 and read-only support when using UDF 2.60. However, Windows does not implement support for certain UDF features such as named streams and access control lists., | {{yes}}| {{yes}}| {{yes}}read only}}| {{yes}}| {{yes}}| Referred to by Microsoft as Live File System.! Operating system! 1.02! 1.50! 2.0x! 2.50! 2.60! VAT! Sparing Tables! Note!! colspan="5" | UDF revision (read + write)! colspan="2" | Non-plain!

See also



Further reading

  • ISO/IEC 13346 standard, also known as ECMA-167.

External links

{{Filesystem}}{{Ecma International Standards}}{{List of International Electrotechnical Commission standards}}

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