| Developer(s) | ISO/IEC,Ecma International,OSTA |
|---|---|
| Full name | Universal Disk Format |
| Introduced | 1995; 30 years ago (1995) |
| Partition IDs | Not assigned but suggested:[1] 0x07 (MBR) EBD0A0A2-B9E5-4433-87C0-68B6B72699C7 (GPT) |
| Limits | |
| Max volume size | 2TiB (with 512-byte sectors), 8 TiB (with 2 KiB sectors, like most optical discs), 16 TiB (with 4 KiB sectors)[a][2] |
| Max file size | 16EiB |
| Max filename length | 255 bytes (path 1023 bytes[b]) |
| Allowed filename characters | Any 16-bitUnicodeCode point excludingU+FEFF andU+FFFE |
| Features | |
| Dates recorded | creation, archive, modification (mtime), attribute modification (ctime), access (atime) |
| Date range |
|
| Date resolution | Microsecond |
| Forks | Yes |
| Attributes | Various |
| File system permissions | POSIX |
| Transparent compression | No |
| Other | |
| Supported operating systems | Various |
Universal Disk Format (UDF) is anopen, vendor-neutralfile system forcomputer data storage for a broad range of media. In practice, it has been most widely used forDVDs and neweroptical disc formats, supplantingISO 9660. Due to its design, it is very well suited to incremental updates on bothwrite-once and re-writableoptical media. UDF was developed and maintained by theOptical Storage Technology Association (OSTA).
In engineering terms, Universal Disk Format is aprofile of the specifications known as ISO/IEC 13346 and ECMA-167.[4]
Normally,authoring software will master a UDF file system in a batch process and write it to optical media in a single pass. But whenpacket writing to rewritable media, such asCD-RW, UDF allows files to be created, deleted and changed on-disc just as a general-purposefilesystem would on removable media likefloppy disks andflash drives. This is also possible on write-once media, such asCD-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.[c]
TheOptical Storage Technology Association standardized the UDF file system to form a common file system for all optical media: both forread-only media and for re-writable optical media. When first standardized, the UDF file system aimed to replaceISO 9660, allowing support for both read-only and writable media. After the release of the first version of UDF, theDVD Consortium adopted it as the official file system forDVD-Video andDVD-Audio.[5]
UDF shares the basicvolume descriptor format with ISO 9660. A "UDF Bridge" format is defined since 1.50 so that a disc can also contain a ISO 9660 file system making references to files on the UDF part.[6]
Multiple revisions of UDF have been released:[5][7]
UDF Revisions are internally encoded asbinary-coded decimals; Revision 2.60, for example, is represented as0x0260.[13]: 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.[13]: 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 as0x0201, the minimum read revision set to0x0150, the minimum write to0x0150, and the maximum write to0x0260.
While UDF was primarily developed for optical discs, it is also able to operate on other media such as hard disk drives and flash storage.[14]
UDF was for well over a decade the only open-specification andcross-platform-supported file system without a file size limitation of 4 GiB (roughly 4.3 GB), until the open-sourcing ofexFAT in 2019.[f] "Cross-platform" here means supported by all three majorly used operating systems, Windows and Mac OS and Linux.[15]
The UDF standard defines threefile system variations, called "builds". These are:
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 ashard disks,DVD+RW andDVD-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 thebasic format, practically any operating system or file system driver claiming support for UDF should be able to read this format.
Write-once media such asDVD-R andCD-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 theplain 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 anISO 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 theVAT build to the UDF standard in its revision 1.5. The VAT is an additional structure on the disc that allowspacket 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.
Rewriteable media such asDVD-RW andCD-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 orCD 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 theVAT 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 theVAT 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.
Thespared build was added in revision 1.5 to address the particularities of rewriteable media. This build adds an extraSparing 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 asMount 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.
Anoverhead that is spread over the entire disc reserves a portion of the data storage space, limiting the usable capacity of aCD-RW with e.g. 650 MB of original capacity to around 500 MB.[16]
The UDF specifications[5] allow only one Character SetOSTA CS0, which can store anyUnicodeCode point excluding U+FEFF and U+FFFE. Additional character sets defined in ECMA-167 are not used.[4]: 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 includesPlane 1–16 characters such asEmoji. DCN-5157 also recommendsnormalizing the strings to Normalization Form C.[17]
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. The 8-bit storage is functionally equivalent toISO-8859-1, and the 16-bit storage isUTF-16 in big endian. 8-bit-per-character file names save space because they only require half the space per character, so they should be used if the file name contains no special characters that can not be represented with 8 bits only.[18]
The reference algorithm neither checks for forbidden code points nor interpretssurrogate pairs, so likeNTFS the string may be malformed.[5]: 2.1.2, 6.4 (No specific form of storage is specified by DCN-5157, but UTF-16BE is the only well-known method for storing all of Unicode while being mostly backward compatible withUCS-2.)[17]
 | This section needs to beupdated. The reason given is: For many operating systems, the information is a decade old and may or may not reflect the current situation accurately. Please help update this article to reflect recent events or newly available information.(November 2020) |
ManyDVD 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 anoperating system claims to be able to read UDF 1.50, it still may only support theplain build and not necessarily either theVAT orSpared UDF builds.
Mac OS X 10.4.5 claims to support Revision 1.50 (seeman mount_udf), yet it can only mount disks of theplain build properly and provides no virtualization support at all. It cannot mount UDF disks with VAT, as seen with the Sony Mavica issue.[19][20] Releases before 10.4.11 mount disks with Sparing Table but does not read its files correctly. Version 10.4.11 fixes this problem.[21][22]
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.[23] 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 this[24] and is included in Service Pack 3.[23]
Due to the default UDF versions and options, a UDF partition formatted by Windows cannot be written under macOS. On the other hand, a partition formatted by macOS cannot be directly written by Windows, due to the requirement of aMBR partition table. In addition, Linux only supports writing to UDF 2.01. A script for Linux and macOS calledformat-udf handles these incompatibilities by using UDF 2.01 and adding a fake MBR;[25] for Windows the best solution is using the command-line toolformat /FS:UDF /R:2.01.
Tools for repairing UDF file systems and for modifying their properties have been made for some operating systems. On Windows, thechkdsk tool is able to repair UDF file systems (if not too damaged, like any file system). A similar tool for Linux,udffsck, was under development by Vojtech Vladyka as an extension offsck, and it was planned to be added to theudftools package. However, it was abandoned by its developer in 2018.[26]
A tool for toggling the write protection flag,udftune, was under development by Johannes Truschnigg in 2023 but could not be merged into the mainudftools package because its maintainer Pali Rohár has reportedly lost access to his GitHub account.[27]
| |||||||||
| UDF revision (read + write) | Non-plain | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| Operating system | 1.02 | 1.50 | 2.0x | 2.50 | 2.60 | VAT | Sparing tables | Note | |
| AIX 5.2, 5.3, 6.1 | Yes | Yes | No | No | 1.5 is default[28] | ||||
| AmigaOS 4.0 | Yes | Yes | |||||||
| BeOS/magnussoft ZETA/Haiku | Yes | Yes | Yes | Yes | Yes | ||||
| OS/2 (includingeComStation andArcaOS) | Yes | Additional fee drivers on OS/2. | |||||||
| FreeBSD 5.0 and newer | read only | read only[29] | No | No | No | No | Yes | ||
| Linux kernel 2.2 | No | No | No | No | No | No | No | ||
| Linux kernel 2.4 | Yes | Yes | Yes[g] | 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[30] | read only[13]: 10 | Yes | Yes | Permission-related mounting options added in 2.6.30.[31] 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 8.1–8.5 | Yes | No | No | No | No | No | No | Some earlier versions of Mac OS, such as7.5, 7.6, and 8.0 are also supported via third-party utilities, along with additional UDF version support for 8.1 and 8.5.[h] | |
| Mac OS 8.6,Mac OS 9 | Yes | Yes | No | No | No | No | No | Additional UDF version support via third-party utilities.[h] | |
| Mac OS X 10.0–10.3 | Yes | Yes[32] | No[32] | No | No | No | No | ||
| Mac OS X 10.4 | Yes | Yes | Yes | No[i][33] | No[j] | No | Yes[k] | Can create UDF 1.50 (plain build) volumes using thedrutil utility. | |
| Mac OS X 10.5 and newer | Yes | Yes | Yes | Yes[34][33] | read only[34][35] | Yes | Yes | To create, usenewfs_udf utility. | |
| NetBSD 4.0 | read only[36] | 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 | Write support for all builds and media including multi-session VAT.[37] Create new withnewfs_udf.Limited writing on 2.50/2.60 (due to needing pre-allocated, fixed sized metadata partition).[38] | |
| NetWare 5.1 | |||||||||
| NetWare 6 | |||||||||
| OpenBSD 3.8–3.9 | read only[39] | No | No | No | No | No | No | ||
| OpenBSD 4.0–4.6 | read only | read only[40] | No | No | No | Yes[40] | No | ||
| OpenBSD 4.7 | read only | read only | read only | read only[41] | read only[41] | Yes | Yes | ||
| Solaris 7 11/99+ | Yes | Yes | |||||||
| Solaris 8/9/10 | Yes | Yes | |||||||
| DOS,FreeDOS,Windows 3.11,Windows 95,Windows 95 OSR2+ and other DOS based OS | No[42] | No | No | No | No | No | No | No native support. Filesystems that have anISO9660 backward compatibility structure can be read. | |
| Windows 98,Windows Me | read only and only for CD/DVD optical disks[43][44][45][42] | No | No | No | No | No | No | Additional read/write support via third party utilities[l] | |
| Windows 2000 | read only[45][46][47][48][42] | read only | No | No | No | No | No | Additional read/write support via third party utilities[l] | |
| Windows XP/Server 2003 | read only[47][48][42] | read only | read only | No | No | Yes | Yes[m] | Additional read/write support via third party utilities[l] | |
| Windows Vista | Yes[49][50][48][42] | Yes | Yes | Yes | read only[49][50][48][42] | Yes | Yes | Referred to by Microsoft asLive File System. Requires fake MBR partition on non-optical devices. | |
| Windows 7 and newer | Yes[42] | Yes | Yes | Yes | Yes | Yes | Yes | ||
| Operating system | 1.02 | 1.50 | 2.0x | 2.50 | 2.60 | VAT | Sparing tables | Note | |
| UDF revision (read + write) | Non-plain | ||||||||
UDF is the "Universal Disk Format" filesystem defined by OSTA, the Optical Storage Technology Association, and is often used for DVD-ROM, frequently in the form of a hybrid UDF/ISO-9660 filesystem. It is, however, perfectly usable by itself on disk drives, flash drives and other block devices.
The output is a drive that can be used for reading/writing across multiple operating system families: Windows, macOS, and Linux. This script should be capable of running in macOS or in Linux.
UDF 1.50 is supported. UDF 2.0 and later is not.
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.
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.
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).
Added UDF support for optical media and block devices, see mount_udf(8). Read-only for now.
Windows 98 has a new read-only Universal Disk Format (UDF) system, which supports reading media formatted according to UDF specification 1.02.
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.
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.
The Windows 2000 UDF file system implementation is ISO 13346-compliant and supports UDF versions 1.02 and 1.5. ... the Windows 2000 UDF driver (Udfs.sys) provides read-only support.
The UDF driver supports UDF versions 1.02, version 1.5 on Windows 2000, and versions 2.0 and 2.01 on Windows XP and Windows Server 2003. ... the Windows UDF driver (Udfs.sys) provides read-only support. Windows does not implement support for other UDF features, including named streams, access control lists, or extended attributes.
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.
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.
udftools and its forks that containudftune andudffsck:ZIP (27 MB),TAR BZip2 (16 MB).Standards ofEcma International | ||
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| Application interfaces |  | |
| File systems (tape) | ||
| File systems (disk) | ||
| Graphics | ||
| Programming languages | ||
| Radio link interfaces | ||
| Other | ||
List of Ecma standards (1961 – present) | ||