8.3

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8.3 is a common shorthand for the limits on filename length imposed by the FAT file system used by DOS and versions of Microsoft Windows prior to Windows 95 and Windows NT 3.5. Similar file naming schemes have also existed on earlier CP/M and on some Data General and Digital Equipment Corporation minicomputer operating systems.

8.3 filenames must have at most eight characters, followed by a ".", followed by a filename extension of at most three characters. File and directory names are uppercase.

VFAT, a variant of FAT with an extended directory format, was introduced in Windows 95 and Windows NT 3.5. It allowed much longer, mixed-case Unicode filenames (LFNs) in addition to classic 8.3 names.

To maintain backward-compatibility with legacy applications (on DOS and Windows 3.1), an 8.3 filename is automatically generated for every LFN, through which the file can still be renamed, deleted or opened.

Although there is no compulsory algorithm for creating the 8.3 name from an LFN, Windows uses the following convention:

1. If the LFN is 8.3 uppercase, no LFN will be stored on disk at all.
   • Example: "TEXTFILE.TXT"
2. If the LFN is 8.3 mixed case, the LFN will store the mixed-case name, while the 8.3 name will be an uppercased version of it.
   • Example: "TextFile.Txt" becomes "TEXTFILE.TXT".
3. The LFN is truncated to the first 6 letters of its basename, followed by a tilde, followed by a single digit, followed by the first 3 characters of the extension. The result is then stripped of invalid characters such as spaces and extra periods, while other characters such as (+) are changed to the underscore (_), and uppercased.
   • Example: "TextFile1.Mine.txt" becomes "TEXTFI~1.TXT" (or "TEXTFI~2.TXT", should "TEXTFI~1.TXT" already exist). "ver +1.2.text" becomes "VER_12~1.TEX".
4. Beginning with Windows 2000, if at least 4 files or folders already exist with the same initial 6 characters in their short names, the LFN is instead truncated to the first 2 letters of the basename (or 1 if the basename has only 1 letter), followed by 4 hexadecimal digits derived from an undocumented hash of the filename, followed by a tilde, followed by a single digit, followed by the first 3 characters of the extension. The result, as before, is stripped and uppercased.
   • Example: "TextFile.Mine.txt" becomes "TE021F~1.TXT".

The NTFS file system used by the Windows NT family supports LFNs natively, but 8.3 names are still available for legacy applications. This can be optionally disabled to increase performance.

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

It is reported that during the Microsoft antitrust trials, the names MICROS~1 and MICROS~2 were used to refer to the companies that might exist after a proposed split of Microsoft.de:8.3 zh:8.3