Microsoft KB Archive/99589

= How Windows NT Generates MS-DOS Compatible Filenames =

Article ID: 99589

Article Last Modified on 10/31/2006

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APPLIES TO


 * Microsoft Windows NT Advanced Server 3.1
 * Microsoft Windows NT Workstation 3.1

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This article was previously published under Q99589



SUMMARY
Windows NT file system (NTFS) filenames do not have the same limitations that MS-DOS FAT style filenames have. MS-DOS style filenames are limited to eight and three character strings separated by a period. NTFS filenames can be much longer and may contain more types of characters. When Windows NT copies a file from an NTFS partition to a FAT partition, it needs to change the filename for compatibility. The following rules are applied when filenames are converted from NTFS to FAT:


 * All spaces in the NTFS filename are removed.
 * All periods except the last one preceding a character are removed.
 * The first three characters following the last period are used for the three letter extension of the FAT filename.
 * All characters that are illegal in FAT but legal in NTFS are replaced with underscore characters (&quot;_&quot;).
 * The first six characters of the NTFS filename, a tilde character (~), and a single digit are used for the eight letter prefix of the FAT filename.

If this does not result in a unique filename, only the first five characters of the NTFS filename are used, followed by the tilde and two digits.

When filenames are moved from a FAT partition to an NTFS partition, no conversion takes place because NTFS fully supports the FAT file naming convention.

Additional query words: prodnt

Keywords: kbother KB99589

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