I have an older WD MyBook and I'm only using about half of its capacity. I don't know much about this sort of thing so I am here to ask for advice. I went to try to do a time machine backup of my MBP and the program tells me I'll have to erase everything on my external HD because it has an incompatible file system. Previously I used the HD with my 2 PC laptops. As I said I'm only using half the capacity and now have 2 MBP's (mine and my wife's) I need to start performing back ups of these. Do I need to invest in another external HD? I'd like to avoid the cost if I can even though the HD I have is older technology and not the highest storage capacity, it seems to suit my needs, for now. If purchasing a new HD is the best route, can you recommend a decent unit? Maybe 1TB and if it can be accessed via wifi between 2 computers that would be nice, but not a necessity. Thanks. PS: I'm not familiar with a lot of technical terms related to computer so hopefully you can explain these things in layman's terms for my idiot self. Thank you again.