The optical drive in my Macbook Pro stopped working. I brought it in to a repair shop and they said it would be costly to repair. I wasn't concerned because I figured I would just buy a USB drive and just use that, but my friend said that the USB drive wouldn't work. Something about Macs can only "see" one drive and since the original s still installed it would ignore any other drive. This doesn't make sense to me, is it true? If it is, could you please explain in more detail why? Thanks 
