In my macbook my external HDD works and is my timemachine drive. I plug in an turn on timemachine an when done turn i o and eject the drive. When I plug drive into the pro i beeps and read light flashes on and off. I wanted to put the backup on my pro. If I take drive from caddy and put in a caddy with dual USB it will work. Do older mac output less power on USB? I used this drive on many windows laptops an tablets with single port fine. They where mostly ewer than 2007 though. I am going to get a 54mm USB 3 card for side of pro. Do you think this will solve the problem?