Where exactly is the "Meta Data" for S3?

Stuffed in the file it's self? A Hidden File? The S3 file system (Linux?) directory? Magic?

Knowing that SyncBack Pro will upload a file again that hasn't changed that was uploaded by another means. Obviously it's having to include it's "special" method of including the Last Access Date/Time.

The concern here is then if the file is downloaded by that "other" means the possibility exists that the file downloaded is not "exactly" what was originally uploaded. I.E. SyncBack Pro "adds" a little something to the copy, somewhere.

It works fine... but inquiring minds wish to know?

Thanks: DES