Transportable media must overcome barriers of physical incompatibility. Today we no longer expect problems like drive alignment to prevent media written on one system from being read on another. What we face instead is a large variety of media types, along with multiple storage methods even on similar physical media. For example:
Sometimes portable drives offer a possible solution, but there is no guarantee that every environment will support the physical interfaces and connectors needed. A Zip drive with a parallel port interface is of little use on a USB only system!