Well, I use a Mac for personal use and have around 30 other Windows PC's in the house and my school uses Windows. I do all my homework on my Mac with Word and needed an external hard-drive for school so I bought one. I needed to print some work in school from my external hard-drive and the work was done from my Mac. The hard-drive wouldn't show up in MY COMPUTER on the Windows PC. Do any of you understand what I just said? Will an external hard-drive only work on one OS?