Files that contain the .009 file extension are most commonly associated with split volume archives files. When a file compression and archive utility is used to combine a batch of files into a single file archive, the resulting archive file can be split into separate volumes. This allows the archive to be distributed more easily via the Web and email.
When an archive file is split, each volume of the archive is given its own extension in sequence. The .009 file extension is most commonly assigned to the ninth volume of the split archive file. All of the archive volumes must be present in order for a user to extract the contents from the original archive file.
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