I'd like to buy a card reader for camera cards (multiformat, if possible) for my iMac 7.1. Because all my USB ports are full (including using a splitter), I'd like one that could run off of one of the unused firewire ports on the back of the computer. But I understand that there is more than one kind of firewire port: 4-pin and 6-pin, and readers need 6-pin. I don't know which I've got. Can anyone recommend a photo card reader that will work with my iMac, or at least tell me which kind of firewire port I have?