DOCUMENT:Q114816  08-AUG-2001  [winnt]
TITLE   :Faster 8.3 Converted Long Filenames in NTFS
PRODUCT :Microsoft Windows NT
PROD/VER:WinNT:3.5,3.51,4.0
OPER/SYS:
KEYWORDS:kbother

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The information in this article applies to:

 - Microsoft Windows NT Workstation versions 3.5, 3.51, 4.0 
 - Microsoft Windows NT Server versions 3.5, 3.51, 4.0 
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SUMMARY
=======

Several Long Filename to 8.3 (MS-DOS compatible) name conversion performance
enhancements have been introduced in Windows NT Workstation and Windows NT
Server version 3.5(and later). These enhancements include a faster worst case
scenario algorithm, as well as improved context retention across enumeration
calls. Although these changes yield substantial improvements, you should
continue to avoid using numerous long, similar names.

MORE INFORMATION
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In Windows NT version 3.1, worst-case file manipulation of extremely large
directories (500 to several thousand files) with similar long names was time
consuming. This was evident when receiving screen output from a DIR command or
reading a directory in File Manager.

In Windows NT 3.5(and later), NTFS has been enhanced to address these worst- case
scenarios as well as other general improvements in 8.3 enumeration.

Under Windows NT 3.1 NTFS, longfile names are converted to 8.3 names to support
DOS based clients. This conversion simply takes the first 6 characters of the
long name, and uses a "~n" suffix (where "n" is number) to keep the name unique
if needed. When the tenth filename is converted and the suffix exceeds 2
characters, only 5 characters of the name are used to accommodate the three
characters in the suffix and so on as needed. For example:

   MyTermPaper.doc   becomes  MYTERM~1.DOC
   MyTermPaper2.doc  becomes  MYTERM~2.DOC
   MyTermPaper3.doc  becomes  MYTERM~3.DOC
   MyTermPaper4.doc  becomes  MYTERM~4.DOC
   MyTermPaper5.doc  becomes  MYTERM~5.DOC
   MyTermPaper6.doc  becomes  MYTERM~6.DOC
   MyTermPaper7.doc  becomes  MYTERM~7.DOC
   MyTermPaper8.doc  becomes  MYTERM~8.DOC
   MyTermPaper9.doc  becomes  MYTERM~9.DOC
   MyTermPaper10.doc becomes  MYTER~10.DOC
   MyTermPaper11.doc becomes  MYTER~11.DOC

That algorithm had been changed in Windows NT 3.5(and later) for enhanced
performance. Since the occurrence of similar 8.3 names is generally minimal,
only the first four attempts at generating the 8.3 name work like they did in
Windows NT 3.1. The fifth attempt takes the first two characters of the long
name, then the next four characters are generated by a hashing function of the
entire name, and the last two characters are "~5". Only when the hashing of the
middle four characters no longer produces a unique name will the "~5" be
incremented to "~6" and so on. For example:

   MyTermPaper.doc   becomes  MYTERM~1.DOC
   MyTermPaper2.doc  becomes  MYTERM~2.DOC
   MyTermPaper3.doc  becomes  MYTERM~3.DOC
   MyTermPaper4.doc  becomes  MYTERM~4.DOC
   MyTermPaper5.doc  becomes  MY1E2E~5.DOC
   MyTermPaper6.doc  becomes  MY1EEE~5.DOC
   MyTermPaper7.doc  becomes  MY1EAE~5.DOC

Subsequent iterations are performed faster than under Windows NT 3.1.

NOTE: By avoiding using long names that are similar in the first 6 characters,
enumeration are even more efficient.

Additional query words: prodnt lfn long name

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Keywords          : kbother 
Technology        : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT351search kbWinNT350search kbWinNT400search kbWinNTW350 kbWinNTW350search kbWinNTW351search kbWinNTW351 kbWinNTSsearch kbWinNTS400search kbWinNTS400 kbWinNTS351 kbWinNTS350 kbWinNTS351search kbWinNTS350search
Version           : WinNT:3.5,3.51,4.0

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