I am not understanding the :url and :path. Where is the root of these paths. ? Clearly for path it is rails root. What do both of these do?? is the url just what is displayed and the path is where they are actually stored?

app_screenshot.rb

has_attached_file :image, :styles => { :small => "480x320>", :large => "920x640>"},
					:url => '/assets/images/:class/:id/:style.:extension',
                    :path => '/:rails_root/assets/images/:class/:id/:style.:extension'