This cable does what it say's - its a serial PC interface cable. Plugs into the 9way 'D' serial connector on the back of your PC (if you still have one!), and connects snuggly to the back of the Garmin GPS (I own a Garmin eTrek H - and it fits fine, without moving around). Once the cable is connected you can download waypoints etc to the GPS, or update the GPS firmware (recommended) etc. NB. This cable does NOT come with any software, if you use the GPS for Geocaching, then you can download waypoints using this cable via the Geocaching website and the Internet explorer plug-in (no software required). :-)