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If you are using the Quick Backup then depending on the version of Maximizer you are using it will either have asked you to specify a location when the backup was triggered or the files will simply be backed up to the database location with a .sav file extension.
To find the database location click File>>Open Address Book and select the address book you've logged into, then click 'Explore', this will open the Windows Explorer to the location that contains all the files.