Editing 8.3 filename (section)

==Overview==
8.3 filenames are limited to at most eight characters (after any directory specifier), followed optionally by a [[filename extension]] consisting of a [[full stop|period]] {{code|.}} and at most three further characters. For systems that only support 8.3 filenames, excess characters are ignored. If a file name has no extension, a trailing {{code|.}} has no significance (that is, {{code|myfile}} and {{code|myfile.}} are equivalent). Furthermore, file and [[directory (file systems)|directory]] names are [[uppercase]] in this system, even though systems that use the 8.3 standard are usually [[case sensitivity|case-insensitive]] (making {{code|CamelCap.tpu}} equivalent to the name {{code|CAMELCAP.TPU}}). However, on non-8.3 [[operating system]]s (such as almost any modern operating system) accessing 8.3 file systems (including DOS-formatted [[floppy disk]]s, but also including some modern memory cards and networked file systems), the underlying system may alter filenames internally to preserve [[case sensitivity|case]] and avoid truncating letters in the names, for example in the case of [[VFAT]].

===VFAT and computer-generated 8.3 filenames===
[[VFAT]], a variant of FAT with an extended directory format, was introduced in [[Windows 95]] and [[Windows NT]] 3.5. It allowed mixed-case [[Unicode]] [[long filename]]s (LFNs) in addition to classic 8.3 names by using multiple [[design of the FAT file system#Directory table|32-byte directory entry records]] for long filenames (in such a way that old 8.3 system software will only recognize one as the valid directory entry).

To maintain backward-compatibility with legacy applications (on [[DOS]] and [[Windows 3.1]]), on FAT and VFAT filesystems, the operating system automatically generates an 8.3 filename for every LFN, through which the file can [also] be opened, renamed, or deleted, although the generated name (e.g. {{code|OVI3KV~N}}) may show little similarity to the original. The generation of 8.3 filenames on NTFS filesystems can be turned off system-wide (with risks).<ref name=Microsoft>{{cite web |title=How to Disable the 8.3 Name Creation on NTFS Partitions |publisher=Microsoft |url=https://www.betaarchive.com/wiki/index.php?title=Microsoft_KB_Archive/121007 |access-date=2021-02-26}}</ref> The 8.3 filename can be obtained using the [[Kernel32.dll]] function GetShortPathName.<ref>{{cite web |title=GetShortPathName Function |publisher=[[MSDN]] |url=http://msdn.microsoft.com/en-us/library/aa364989.aspx |access-date=2014-09-15 |url-status=dead |archive-url=https://web.archive.org/web/20151001002209/https://msdn.microsoft.com/en-us/library/aa364989.aspx |archive-date=2015-10-01}}</ref><ref>{{cite web |title=How to Get a Short Filename from a Long Filename |publisher=Microsoft |url=https://www.betaarchive.com/wiki/index.php?title=Microsoft_KB_Archive/175512 |access-date=2021-02-26}}</ref>

Although there is no compulsory [[algorithm]] for creating the 8.3 name from an LFN, Windows uses the following convention:<ref>{{cite web |title=How Windows Generates 8.3 File Names from Long File Names |publisher=Microsoft |url=https://www.betaarchive.com/wiki/index.php?title=Microsoft_KB_Archive/142982}}</ref>
# If the LFN is 8.3 uppercase, no LFN will be stored on disk at all.
#* Example: {{code|TEXTFILE.TXT}}
# If the LFN is 8.3 mixed case, the LFN will store the mixed-case name, while the 8.3 name will be an uppercase version of it.
#* Example: {{code|TextFile.Txt}} becomes {{code|TEXTFILE.TXT}}.
# If the LFN contains more than 8 characters, [[Illegal character|invalid characters]] such as space (which was disallowed by convention though not by the APIs) and those disallowed within [[#Directory table|directory tables]], or an extension more than 3 characters long, the name is stripped of its invalid characters. If the name begins with periods {{code|.}} the leading periods are removed. Other characters such as {{code|+}} are changed to the [[underscore]] {{code|_}}, and letters are put in uppercase. The stripped name is then truncated to the first 6 characters of its [[basename]], followed by a [[tilde]], followed by a single [[numerical digit|digit]], followed by a period {{code|.}}, followed by the first 3 characters of the extension.
#* Example: {{code|TextFile.Mine.txt}} becomes {{code|TEXTFI~1.TXT}} (or {{code|TEXTFI~2.TXT}}, should {{code|TEXTFI~1.TXT}} already exist). {{code|ver +1.2.text}} becomes {{code|VER_12~1.TEX}}. {{code|.bashrc.swp}} becomes {{code|BASHRC~1.SWP}}
# On all NT versions including [[Windows 2000]] and later, if at least 4 files or folders already exist with the same extension and first 6 characters in their short names, the stripped LFN is instead truncated to the first 2 characters of the basename (or 1 if the basename has only 1 character), followed by 4 [[hexadecimal]] digits derived from an undocumented hash of the filename, followed by a tilde, followed by a single digit, followed by a period {{code|.}}, followed by the first 3 characters of the extension.<ref>{{cite web |last1=Galvin |first1=Thomas |date=9 June 2015 |title=A Tale of Two File Names |url=https://tomgalvin.uk/blog/gen/2015/06/09/filenames/ |archive-url=https://web.archive.org/web/20230825135743/https://tomgalvin.uk/blog/gen/2015/06/09/filenames/ |archive-date=2023-08-25 |access-date=17 October 2022 |website=tomgalvin.uk}}</ref><!-- what if this clashes?-->
#* Example: {{code|TextFile.Mine.txt}} becomes {{code|TE021F~1.TXT}}.
# On Windows 95, 98 and ME, if more than 9 files or folders with the same extension and first 6 characters and in their short names (so that {{code|~1}} through {{code|~9}} suffixes aren't enough to resolve the collision), the name is further truncated to 5 letters, followed by a tilde, followed by two digits starting from 10, followed by a period {{code|.}} and the first 3 characters of the extension.
#* Example: {{code|TextFile.Mine.txt}} becomes {{code|TEXTF~10.TXT}} if {{code|TEXTFI~1.TXT}} through {{code|TEXTFI~9.TXT}} all exist already.

During the [[United States v. Microsoft Corp.|2001 Microsoft antitrust case]], the names MICROS~1 and MICROS~2 were humorously used to refer to the companies that might exist after a proposed split of Microsoft.<ref>{{cite web |title=Microsoft One-liner Digest |url=http://www.netfunny.com/rhf/jokes/00/Jun/ms.html}}</ref>

[[NTFS]], a file system used by the [[Windows NT]] family, supports LFNs natively, but 8.3 names are still available for legacy applications. Windows [[NTVDM]] are known to use 8.3 names. This can optionally be disabled system-wide to improve performance in situations where large numbers of similarly named files exist in the same folder.<ref name=Microsoft/> 8.3 filename creation can be disabled system-wide and/or per-volume, and existing 8.3 filenames can be stripped using {{code|fsutil}} or a Registry key.<ref>{{cite web |title=Under cmd.exe, how can "del *.tmp" be prevented from deleting *.tmpl files? |website=superuser |url=https://superuser.com/questions/1644682/under-cmd-exe-how-can-del-tmp-be-prevented-from-deleting-tmpl-files}}</ref>

The [[ISO 9660]] file system (mainly used on [[compact disc]]s) has similar limitations at the most basic Level 1, with the additional restriction that directory names cannot contain extensions and that some characters (notably [[hyphen]]s) are not allowed in filenames. Level 2 allows filenames of up to 31 characters, more compatible with classic AmigaOS and [[classic Mac OS]] filenames.

On [[VFAT]] and [[NTFS]] file systems, 8.3 filenames are stored as ANSI encoding, for backward-compatibility.

The [[ReFS]] no longer supports 8.3 filenames.