The .001 file extension is often given to files that are from a split file archive or to files that have been created by a backup utility.
When a user creates a copy of his or her hard drive with a backup utility, the resulting file is normally too large to maintain in a single file. Because of this, the file is split down into smaller archive files, with each file being given its own extension. The .001 extension is normally given to the first file of the split file archive. Norton Ghost is one of the programs known to use this file extension for this purpose.
Some digital fax files also may contain the .001 extension.
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If you have additional information about the 001 file format or software that uses files with the 001 suffix, please do get in touch - we would love hearing from you.