View source for Long filename

{{Short description|Extension of the 8.3 file naming scheme}}
{{more citations needed | date=February 2015}}
{{Use dmy dates|date=July 2019|cs1-dates=y}}
{{Use list-defined references|date=December 2021}}

'''Long filename''' ('''LFN''') support is [[Microsoft]]'s backward-compatible extension of the [[8.3 filename]] (short filename) naming scheme used in [[MS-DOS]]. Long filenames can be more descriptive, including longer [[filename extension]]s such as <code>[[.jpeg]]</code>, <code>[[.tiff]]</code>, and <code>[[.html]]</code> that are common on other operating systems, rather than specialized shortened names such as <code>.jpg</code>, <code>.tif</code>, or <code>.htm</code>. The standard has been common with [[File Allocation Table]] (FAT) [[filesystem]]s since its first implementation in [[Windows NT 3.5]] of 1994.

To maintain compatibility with older operating systems, Microsoft formulated a method of generating an 8.3 filename from the long filename (for example, <code>Microsoft.txt</code> to <code>MICROS~1.TXT</code>) and associating it with the file.

{{details | VFAT design{{!}}Design of the FAT file system § VFAT long file names}}

==Compatibility issues==
Microsoft implemented support for LFNs in the FAT filesystem by using hidden directory entries, of the ''volume label'' type, to store the longer names; this scheme is known as [[VFAT]], and was chosen for compatibility, as volume labels are generally ignored by programs and [[operating system]] (OS) components. Programs running on older OSs could still access the files' short names, while newer, LFN-aware OSs and programs could use the longer ones.

When LFN support was first introduced into a [[DOS]]-based operating system in the form of [[Windows 95]], it caused some problems for older programs. For example, a DOS program performing sector-level directory operations while Windows was in DOS mode could destroy long filename information so, by default, sector-level access to hard disks was disallowed in this mode.

Upon booting into plain DOS, the long filenames are not visible unless a VFAT LFN driver is installed. Microsoft did not add LFN support to many of its older programs, including [[File Manager (Windows)|File Manager]], the [[Windows 3.1x]] (Windows for Workgroups) file manager that was made obsolete by the new operating system shell, [[Windows Explorer]]. [[Windows NT]] supported LFNs on NTFS file systems starting with the release of NT 3.1, and all of its utilities, including File Manager, were updated to support LFNs. NT 3.5 added FAT LFN support in preparation for Windows 95. However, the Windows 95 version of File Manager came from Windows for Workgroups 3.11.

[[OS/2]] stores LFNs for FAT filesystems in <code>.LONGNAME</code> [[extended attribute]]s that are incompatible with Microsoft's implementation and only visible to tools supporting OS/2's standard. Many APIs providing access to files by pathname cannot see the new, longer names without a supporting driver.

===Limits===
Because the FAT LFN implementation is layered atop an older, more limited naming system, there are inevitable complications, such as if an attempt is made to create too many files with the same first six letters.<ref name="Cocoa_2005"/> Also, one is more likely to encounter issues creating files or folders in the root directory, since [[FAT12]] and [[FAT16]] only allocate space for 512 root directory entries on hard disks.  Since long filenames use more than one directory entry, this problem may occur with fewer than 512 files or folders in the root directory.<ref name="Microsoft_KB120138"/> There is space only for 24 long filenames of maximum length (512/(1+20)). This problem does not exist for [[FAT32]] volumes.

The long filename system allows a maximum length of 255 [[UCS-2]] characters<ref name="Microsoft_ms810456"/><ref name="Dobiash_1998"/> including spaces and non-alphanumeric characters (excluding the following characters, which have special meaning within the [[COMMAND.COM]] command interpreter or the operating system kernel: <code>\ / : * ? " < > |</code>). This is achieved by chaining up to 20 directory entries of 13 2-byte [[Unicode]] characters each.<ref name="Dobiash_1998"/> The maximum length of a pathname is 256 characters, which includes all parent directories and the filename. 255-character mixed-case long filename is possible only for files, or folders with no sub-folders, at the root folder of any drive.

While long filename support allows for longer file and directory names, under DOS-based systems, the ''absolute'' file path constructed from the associated short file and directory name equivalents is still represented in an internal data structure called the [[Current Directory Structure]] (CDS),<ref name="Schulman_1994_Undocumented-DOS"/><ref name="Brown_2000_RBIL"/><ref name="Paul_1997_NWDOSTIP"/><ref name="Paul_1997_NWDOS7UN"/> which imposes a limit of 66 characters on the (short) path name and thereby indirectly limits also the path ''depth'' to a maximum of 33<!-- TBD: or 34? --> levels (counting in the root directory and assuming only single-letter names). (This design limitation was not present in older versions of [[DR&nbsp;DOS]] (prior to DR&nbsp;DOS 6.0 November 1991 updates) which still utilized a ''relative'' path representation internally,<ref name="Paul_1997_NWDOSTIP"/><ref name="Paul_1997_NWDOS7UN"/><ref name="4DOS_8.00_HELP"/> however, due to their internal differences these versions are not compatible with existing LFN add-on drivers.) Non-DOS-based operating systems without a CDS are not restricted to this path depth limitation.

==VFAT LFN drivers==
The following is a list of drivers that can be used to provide support for VFAT long file names as used in Windows 95. Although drivers such as DOSLFN can be loaded in almost any versions of DOS, it works best on DOS versions that have support for LFN themselves, such as [[MS-DOS 7.10]] or [[DR-DOS 7.02]], so that DOS commands such as <code>DIR</code> would show long file names as well.

{| class="wikitable"
!OS
!Driver name
!Provider
|-
|any plain [[DOS]]
|DOSLFN, LFNDOS
|third-party
|-
|[[DR-DOS]]
|LONGNAME
|included
|-
|[[RxDOS]]
|built-in
|included
|-
|[[OS/2]]
|VFAT-OS2.IFS
|third-party
|-
|[[Windows NT 4.0]]
|NTLFN
|third-party
|}

== Driver-less real mode DOS LFN commands ==
Some small real mode DOS programs have also been written over the years, although many have been lost over time. One notable collection of programs that still exists is LFN Tools, which is open source and comprises seven useful LFN commands written in C++ and assembly language, with documentation included in English and German, and is available at LFNTOOLS on Sourceforge.net.

=={{anchor|descript.ion}}Other implementations==
Before LFN support was implemented into the FAT family of file systems, various file managers provided their own methods to attach and maintain longer file descriptions.  Among the first to do so are the alternative command line processors [[4DOS]] and [[NDOS]] with their internal <code>DESCRIBE</code> command and corresponding <code>[[DESCRIPT.ION]]</code> files. The latter are optional hidden files located in each directory storing a line-based list of file names located in the directory together with their textual description and optional [[metadata]] entries—for example, extended attributes and configuration data for other programs.<ref name="JP_1989_DESC"/> The descriptions can be up to 511 characters long and are displayed along the file names in much the same way as long file names are listed alongside their short filename aliases in <code>DIR</code> listings. If an entry exists for a file, it will be copied and moved with the file for as long as these command line processors are used to perform the operation.<ref name="4DOS_8.00_HELP"/> This scheme is still maintained by successors such as [[4OS2]], [[Take Command Console|4NT / Take Command]]. It was adopted also by various other programs like [[Volkov Commander]] (VC), [[DOS Navigator]] (DN), [[Open DOS Navigator]] (ODN), [[Necromancer's DOS Navigator]] (NDN), [[Windows Commander]], [[Total Commander]], [[Double Commander]], [[7-Zip]], [[XnView]], [[ACDSee]], [[Newsbin Pro]], V, [[FreeDOS]]<ref name="FreeCom"/> and some CUI_LIB<ref name="Paul_1997_4DOSTIP"/>-based applications.

{{anchor|18.3}}[[Human68K]], the operating system of the [[X68000]] computers since 1986, is based on an extended FAT file system.  It allows up to 18.3 characters in a filename (instead of the 8.3 in FAT) and allows also upper and lower case characters (as well as [[Kanji]] in [[Shift JIS]] code) that are all treated as distinctive. If restricted to the use of 8.3-format filenames with upper case characters only, the Human68K floppies are fully compatible with the Japanese 1232 KiB standard FAT [[List of floppy disk formats|floppy format]] (77 cylinders, 2 heads, 8 sectors, 1024 bytes/sector). This format is used by the [[NEC PC-9800]], [[Fujitsu FMR]] and [[FM Towns]] series computers.{{citation needed | date=February 2015}}

[[Novell NetWare]] versions 3.x and 4.x [[NetWare File System|volumes]] can also support Microsoft-compatible long filenames, by loading an additional [[NetWare Loadable Module]] (NLM).<ref name="NetWare"/>

In order to support [[Java (programming language)|Java]] applications without implementing a [[VFAT]]-compatible scheme, the [[FlexOS]]-based [[IBM 4690 OS]] version 2 introduced its own [[virtual file system]] (VFS) architecture to store long filenames in the FAT file system in a backwards compatible fashion. If enabled, the virtual filenames (VFN) are available under separate logical drive letters, whereas the real filenames (RFN) remain available under the original drive letters.<ref name="IBM_4690_Programming_Guide"/>

==See also==
* [[TRANS.TBL]]
* [[Rock Ridge]]
* [[Joliet (file system)]]
* [[Romeo (file system)]]
* [[6.3 filename]]
* [[VFAT patent]] issues
* [[Design of the FAT file system]]
* [[File system]]
* [[Large file support]] (LFS)

==References==
{{Reflist|refs=
<ref name="Cocoa_2005">{{cite web |title=MSDOSFileSystem |date=2005-09-12 |work=CocoaDev |url=http://www.cocoadev.com/index.pl?MSDOSFileSystem |url-status=dead |archive-url=https://web.archive.org/web/20061018063912/http://www.cocoadev.com/index.pl?MSDOSFileSystem |archive-date=2006-10-18}}</ref>
<ref name="Dobiash_1998">{{cite web |title=Long Filename Specification |editor-first=Jack "vinDaci" |editor-last=Dobiash |publication-place=Grand Ronde, Oregon, USA |edition=4 |orig-date=1996-11-18 |date=1998-01-06 |url=http://home.teleport.com/~brainy/lfn.htm |access-date=2013-05-22 |url-status=dead |archive-url=https://web.archive.org/web/20151025195158/http://home.teleport.com/~brainy/lfn.htm |archive-date=2015-10-25}}</ref>
<ref name="Microsoft_KB120138">{{cite web |title=Errors Creating Files or Folders in the Root Directory |publisher=[[Microsoft]] |id=120138 |url=http://support.microsoft.com/kb/120138 <!-- |url-status=dead -->}}</ref>
<ref name="Microsoft_ms810456">{{cite web |title=Making Room for Long Filenames |department=Files and I/0 Technical Articles |author-first=Nancy |author-last=Winnick Cluts |date=August 1996 |orig-date=January 1995 |id=810456 |publisher=[[Microsoft Corporation]] |url=http://msdn2.microsoft.com/en-us/library/ms810456.aspx |access-date=2007-04-19 |url-status=dead |archive-url=https://web.archive.org/web/20080423090226/http://msdn2.microsoft.com/en-us/library/ms810456.aspx |archive-date=2008-04-23}}</ref>
<ref name="4DOS_8.00_HELP">{{cite book |title=4DOS 8.00 online help |title-link=4DOS 8.00 |author-first1=Hardin |author-last1=Brothers |author-first2=Tom |author-last2=Rawson |author-link2=Tom Rawson |author-first3=Rex C. |author-last3=Conn |author-link3=Rex C. Conn |author-first4=Matthias R. |author-last4=Paul |author-first5=Charles E. |author-last5=Dye |author-first6=Luchezar I. |author-last6=Georgiev |date=2002-02-27}}</ref>
<ref name="Paul_1997_4DOSTIP">{{cite web |title=Hinweise zu JPSofts 4DOS 5.5b/c, 5.51, 5.52a und NDOS |work=MPDOSTIP |author-first=Matthias R. |author-last=Paul |date=1997-05-01 |orig-date=1995-03-01 |language=de |url=http://www.antonis.de/dos/dos-tuts/mpdostip/html/4dostip.htm |access-date=2015-05-08 |url-status=live |archive-url=https://web.archive.org/web/20161104211143/http://www.antonis.de/dos/dos-tuts/mpdostip/html/4dostip.htm |archive-date=2016-11-04}} (NB. The provided link points to a HTML-converted version of the <code>4DOS5TIP.TXT</code> file, which is part of the <code>MPDOSTIP.ZIP</code><!-- still named TIPS_MP.ZIP between 1991 and 1996-11 --> collection.) [https://web.archive.org/web/20190601152204/https://www.sac.sk/download/text/mpdostip.zip<!-- A yet older version 155 from 1997-05-13 of the 1997-07-15 distribution archive. -->]</ref>
<ref name="FreeCom">{{cite web |title=FreeCom and 4DOS DESCRIPT.ION files |url=http://freedos.gds.tuwien.ac.at/freedos/news/technote/225.html |access-date=2016-11-11 |author-first=Jeremy |author-last=Davis |publisher=[[FreeDOS]] |type=FreeDOS tech note |url-status=live |archive-url=https://web.archive.org/web/20161111214239/http://freedos.gds.tuwien.ac.at/freedos/news/technote/225.html |archive-date=2016-11-11}}</ref>
<ref name="NetWare">{{cite web |url=http://www.novell.com/support/search.do?cmd=displayKC&docType=kc&externalId=1002030&sliceId=&dialogID=52309057&stateId=0%200%2052303960 |title=TID1002030 Windows NT, Long File Names on NetWare |author=Novell |author-link=Novell |date=1999-02-11 |access-date=2007-12-03  |archive-date=2011-06-06  |archive-url=https://web.archive.org/web/20110606134839/http://www.novell.com/support/search.do?cmd=displayKC&docType=kc&externalId=1002030&sliceId=&dialogID=52309057&stateId=0%200%2052303960 |url-status=dead }}</ref>
<ref name="IBM_4690_Programming_Guide">{{cite book |publisher=[[IBM]] |title=4690 OS Programming Guide Version 5.2 |id=IBM document SC30-4137-01 |date=2007-12-06 |url=https://public.dhe.ibm.com/software/retail/pubs/sw/opsys/4690/ver5r2/bsi1_PG_mst.pdf |url-status=live |access-date=2018-09-03  |archive-date=2022-01-25  |archive-url=https://web.archive.org/web/20220125063705/ftp://ftp.software.ibm.com/software/retail/pubs/sw/opsys/4690/ver5r2/bsi1_PG_mst.pdf }}</ref>
<ref name="JP_1989_DESC">{{cite web |title=Technical Note -- Using DESCRIPT.ION |date=1989 |publisher=[[JP Software Inc.]] |location=Chestertown, Maryland, USA |url=https://jpsoft.com/ascii/descfile.txt |url-status=dead |archive-url=https://web.archive.org/web/20160318122322/https://jpsoft.com/ascii/descfile.txt |archive-date=2016-03-18}} (NB. Known IDs include <code>0x23</code> ('#') as used by various utilities written by Matthias R. Paul for space-separated lists of text [[key=value pair]]s holding file properties as [[extended attribute]]s like CP (codepages), PC (language codes), CW (bit-width), XS (page width), YS (page length), XO (print x-offset), YO (print y-offset), CR (copyright), URL (source link), etc.<!-- Examples: https://web.archive.org/web/20210227002211/http://www.ibiblio.org/pub/micro/pc-stuff/freedos/files/util/print/cpi/NECPI208.ZIP https://web.archive.org/web/20160420065252/http://www.columbia.edu/~em36/wpdos/MatthiasPaulCPI.zip https://web.archive.org/web/20190601152204/https://www.sac.sk/download/text/mpdostip.zip -->, <code>0x25</code> ('%') being used by programs using CUI_LIB to store [[pseudo-environment variable]]s, <code>0xED</code> being reserved for [[Digital Research]]/[[Novell]]/[[Caldera (company)|Caldera]] and <code>0xFD</code> for [[FreeDOS]].)</ref>
<ref name="Schulman_1994_Undocumented-DOS">{{cite book |author-first1=Andrew |author-last1=Schulman |author-first2=Ralf D. |author-last2=Brown |author-link2=Ralf D. Brown |author-first3=David |author-last3=Maxey |author-first4=Raymond J. |author-last4=Michels |author-first5=Jim |author-last5=Kyle |title=Undocumented DOS: A programmer's guide to reserved MS-DOS functions and data structures - expanded to include MS-DOS 6, Novell DOS and Windows 3.1 |publisher=[[Addison Wesley]] |edition=2 |date=1994 |orig-date=November 1993<!-- first printing --> |isbn=0-201-63287-X |id={{ISBN|978-0-201-63287-3}} |location=Reading, Massachusetts |url-access=registration |url=https://archive.org/details/undocumenteddosp00andr_0}} (xviii+856+vi pages, 3.5-inch floppy) Errata: [https://web.archive.org/web/20190417215556/http://www.cs.cmu.edu/afs/cs/user/ralf/pub/books/UndocumentedDOS/errata.ud2][https://web.archive.org/web/20190417212906/https://www.pcjs.org/pubs/pc/programming/Undocumented_DOS/#errata-2nd-edition]</ref>
<ref name="Paul_1997_NWDOSTIP">{{cite book |title=NWDOS-TIPs &mdash; Tips & Tricks rund um Novell DOS 7, mit Blick auf undokumentierte Details, Bugs und Workarounds |series=MPDOSTIP |author-first=Matthias R. |author-last=Paul |date=1997-07-30 |orig-date=1994-05-01 |edition=3 |language=de |url=http://www.antonis.de/dos/dos-tuts/mpdostip/html/nwdostip.htm |access-date=2014-08-06 |url-status=live |archive-url=https://web.archive.org/web/20170910194752/http://www.antonis.de/dos/dos-tuts/mpdostip/html/nwdostip.htm |archive-date=2017-09-10}} (NB. NWDOSTIP.TXT is a comprehensive work on Novell DOS 7 and OpenDOS 7.01, including the description of many undocumented features and internals. It is part of the author's yet larger <code>MPDOSTIP.ZIP</code><!-- still named TIPS_MP.ZIP between 1991 and 1996-11 --> collection maintained up to 2001 and distributed on many sites at the time. The provided link points to a HTML-converted older version of the <code>NWDOSTIP.TXT</code> file.) [https://web.archive.org/web/20190601152204/https://www.sac.sk/download/text/mpdostip.zip<!-- A yet older version 155 from 1997-05-13 of the 1997-07-15 distribution archive. -->]</ref>
<ref name="Paul_1997_NWDOS7UN">{{cite book |title=NWDOS7UN.TXT — Zusammenfassung der dokumentierten und undokumentierten Fähigkeiten von Novell DOS 7 |series=MPDOSTIP |chapter=Chapter 1.3.xi: Überlange Pfade |author-first=Matthias R. |author-last=Paul |date=1997-06-07 |orig-date=April 1994 |language=de |url=http://www.antonis.de/dos/dos-tuts/mpdostip/html/nwdos7un.htm |access-date=2016-11-07 |url-status=live |archive-url=https://web.archive.org/web/20161107122352/http://www.antonis.de/dos/dos-tuts/mpdostip/html/nwdos7un.htm |archive-date=2016-11-07}}</ref>
<ref name="Brown_2000_RBIL">{{cite web |title=Ralf Brown's Interrupt List |editor-first1=Ralf D. |editor-last1=Brown |editor-link1=Ralf D. Brown |display-editors=etal |edition=61 |id=[[INTER61]] |date=2000-07-16 |url=https://www.cs.cmu.edu/~ralf/files.html}}</ref>
}}

==External links==
* [http://www.faqs.org/docs/Linux-HOWTO/Filesystems-HOWTO.html The filesystems howto]
* [http://www.ibiblio.org/pub/micro/pc-stuff/freedos/files/util/system/doslfn/ Current version of DOSLFN]
* [http://www-user.tu-chemnitz.de/~heha/hs_freeware/freew.html Original Author of DOSLFN] {{Webarchive|url=https://web.archive.org/web/20130528173924/http://www-user.tu-chemnitz.de/~heha/hs_freeware/freew.html |date=2013-05-28  }}
* [http://www.dsteiner.com/products/software/os2/vfat.htm VFAT OS2 Provides LFN support under OS2]

{{Computer files}}

[[Category:Windows architecture]]
[[Category:Filenames]]