Does a FireWire device need to be turned on, before it is connected to the FireWire port?
If the device is designed according to the FireWire standard, then it does not need to be turned on before it is connected to the computer. The computer can tell the difference between a device that is connected and not turned on, and a device that is connected and turned on. In practice, though, most devices profit from being turned on at the time they are connected.
