Both. Firewire in, USB out. You will only be as fast as the slowest portion to the external. If Firewire is faster you will have the in-between file on the laptop done before it is done on the USB step. If the USB is faster it will be waiting for the Firewire. I would do it in two steps as the MS operating systems do not run two simultaneous precesses well. You will get it done faster if you load the laptop first and then xfer out on the USB.