Prime Infrastructure stores the backups as records in its Oracle database. The supported method for seeing them is via the GUI.
Look under Inventory > Configuration Archive for the individual devices and you will see several options for seeing the configurations of a given device (raw, processed, compare two configs, etc.).
There is a method for extracting all of the configuration files into a zipped file but it involves querying the Oracle database from the cli and is not recommended for the non-expert or casual user.
