Attributes based on the Data Attribute Type store binary information.  Several system Attributes are based on the Data Attribute Type, but you can't create additional Attributes of this Attribute Type.

 

The URL Attribute is a special Attribute based on the Data Attribute Type, because it also functions like a String Attribute, but for an Info Item based on the Document Template Group, also contains the actual document contents when the Store Contents option is checked.  If the binary data stored for this Attribute can be modified, it can only be edited in the Item Details Pane (or externally if this option is enabled for the particular file type).