I do not know how they are made, however they do make external hard drives for the gl2. Though they are very expensive. You CAN record and output video at the same time. We have recorded and output via firewire to a computer to project onto a screen. In the menu there is an option to turn on and off the dv control which is for controlling the external hard drive. If anyone knows how to make an external hard drive that will do this for under $500 we would appreciate the information.