Right. So check it: every external drive you've ever seen is an internal drive with a dingus attached. That dingus takes it from SATA (typically) to USB or Firewire or Thunderbolt or whatever. Probably less of a problem with USB, but with Firewire it really fucking matters. For the longest time those of us who dealt with media and macs shared little lists of who was using a particular chip (Oxford 911). That only covers Firewire, though, and has long since been superseded. Seagate USB drivers are flaky as fuck. I've got like four WD Mybooks, all of them triple interface (USB3, Firewire 800, eSATA). The USB interface is usually great but slower than eSATA. Firewire works so long as you aren't expecting to use it for Time Machine that much. Probably not problems you run into on the PC side, but here in the land of Mac it matters.