If this has been discussed before bare with me. I found out the hard way. I have external drives both optical and HDD that are externally powered so I didn’t pick up on this right away. I plugged into a four port USB adapter and began backing up a movie. At some stage of completion it just froze up, locked up! The four port adapter is an older un-powered 1.1 adapter I later found out. When I plugged straight into the 2.0 port on the computer all went as planned. So I tried again using the DVD drive and the HDD, both hit the 1.1 data bottleneck, different movies at different stages of completion. I put a Hi-Speed 2.0 adapter on and again all went as planned. In my case at any rate USB 1.1 is just not fast enough to move the data required for a movie backup. Be sure you use a USB 2.0 port and be advised that not all multi-port adapters are Hi-Speed 2.0. If you are having these mysterious lockups on external devices, might be worth a look.