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How Windows Generates 8.3 File Names from Long File Names

This article was previously published under Q142982
Windows supports long file names up to 255 characters in length.Windows also generates an MS-DOS-compatible (short) file name in8.3 format to allow MS-DOS-based or 16-bit Windows-based programs toaccess the files.
Windows generates short file names from long file names in thefollowing manner:
  • Windows deletes any invalid characters and spaces from the file name. Invalid characters include:
    . " / \ [ ] : ; = ,
  • Because short file names can contain only one period (.), Windows removes additional periods from the file name if valid, non-space characters follow the final period in the file name. For example, Windows generates the short file name
    from the long file name
    This is a really long filename.123.456.789.txt
    Otherwise, Windows ignores the final period and uses the next to the last period. For example, Windows generates the short file name
    from the long file name
    This is a really long filename.123.456.789.
  • Windows truncates the file name, if necessary, to six characters and appends a tilde (~) and a digit. For example, each unique file name created ends with "~1." Duplicate file names end with "~2," "~3," and so on.
  • Windows truncates the file name extension to three characters or less.
  • Windows translates all characters in the file name and extension to uppercase.
Note that if a folder or file name contains a space, but less than eightcharacters, Windows still creates a short file name. This behavior maycause problems if you attempt to access such a file or folder over anetwork. To work around this situation, substitute a valid character, suchas an underscore (_), for the space. If you do so, Windows does notcreate a different short file name

For example, "Afile~1.doc" is generated from "A file.doc" because the longfile name contains a space.

No short file name is generated from "A_file.doc" because the file namecontains less than eight characters and does not contain a space.

The short file name "Alongf~1.txt" is generated from the long file name "Along filename.txt" because the long file name contains more than eightcharacters.
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Article ID: 142982 - Last Review: 01/19/2007 17:41:37 - Revision: 1.3

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