QuickTime Virtual Reality is a subset of the functionality of Apple Quicktime for non linear movie files. They also have the extension .mov but need QuickTime installed to be viewed. Very basic QTVR panoramas can also be viewed using PTViewer. QTVR refers to the ability to display spherical panoramas in Cubic Projection, cylindrical, partial panoramas, multinode panoramas and objects in a viewer where the user can move around using the mouse and keyboard. The panoramas can be linked through hotspots in order to move from one panorama file to the other or link several panoramas in one multinode file.