Files that contain the .old file extension are most commonly used to indicate that a file on a user's hard drive is a backup copy of a newer version of the file. The .old extension is given to the file name when the newer version of the file is saved within the associated computer application.
The initial file extension is often kept intact when the .old file extension is assigned to a file. For example, if the original version of a file is saved as mydocument.doc, then when a new version of the file is created that version will also be saved with the name of mydocument.doc. However, in order to store a copy of the old version of the file, the original version will be saved with the name as mydocument.doc.old.
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