Windows Tips: Safer Backups--The Long and Short of It

In October's Windows Tips, I described a simple way to back up data files using xcopy32 in the command line. But as reader Jim Barr of Salinas, California, notes, backing up data by using xcopy, xcopy32, Windows Explorer, or even many commercial programs can cause problems due to the way Windows handles long file names.

Here's the scoop: Every time you give a file a name longer than 11 characters (8 characters to the left of the period and the 3-character file-type extension to the right), Windows generates a short 8.3 version of the file name (8 characters plus the 3-letter extension) so that the name will remain compatible with older applications.

Windows removes spaces and other illegal characters, and if the original name has more than 8 characters to the left of the dot, Windows replaces all the characters after the first six with a tilde (~) and a number. For example, a file named 'Florida Polling Data.xls' also has a short file name: 'FLORID~1.XLS'.

You can see these short names by opening the DOS prompt, navigating to a folder, typing dir, and pressing Enter to view a list of folder contents. The short DOS-like names are on the left, and the normal, long Windows names are on the right.

Unfortunately, when many applications make copies of files, they create these short names anew rather than copying the existing short names. So if, for example, you have a folder containing three files named document1.doc, document2.doc, and document3.doc, the short names stored for these files are DOCUME~1.DOC, DOCUME~2.DOC, and DOCUME~3.DOC.

But if you delete document1.doc and use Explorer or xcopy to back up document2.doc and document3.doc to another folder, the new name generated for document3.doc is DOCUME~1.DOC. This means the short name DOCUME~1.DOC could point to document1.doc in one folder and to document3.doc in another folder.

If you back up only data files and you always use Windows programs that are savvy about long file names, chances are you won't have a problem, since those applications won't ever refer to the potentially mixed-up short names. But system files are another story. In many cases, Windows' Registry stores the path to files using their short names.

To see this, choose Start, Run, type regedit, and press Enter. In the Registry Editor, select Edit, Find, type ~, and press Enter. You'll have no trouble finding files and folders that use short names. As a result, it's possible for program and system file names that have been copied and restored to stop functioning because the Registry is using the wrong short form.

The best solution is to make sure you use a backup program that copies the existing short file name along with the long file name; Symantec's Norton Ghost and Norton Ghost 2001 both do this.

For batch-file or simple command-line copying, I like Pixelab's Xxcopy, which at the time of this writing is still freeware. Xxcopy uses the same DOS commands that xcopy does. It preserves short file names, and it has a few other bells and whistles that make it a convenient backup utility. You can download it from our Downloads library, or contact its creators.