FWIW, regardless of the # of ports on the back, your mac only has 1 firewire bus (imac, mini, powermac - powermac also has a firewire 800 bus). If you've got 1 port or 2, 3, etc, it's all sharing the same 400mbits/sec. Also, Firewire is generally preferred over USB - Firewire supplies 400mbps continuous bandwidth, USB2's 480mbps is only in bursts. Also, USB2 requires more CPU power to handle data transaction.