I am new to the Mac and trying to set up time machine. The 500 MB external hard drive I have has about 250 GB of back ups from my pc. When I tried to set up time machine it said it would need to delete the files from the pc from my external hard drive. Is there any way to keep the files from my pc and use the remaining 250 GB of space to do a back up via the time machine. Does time machine require an external hard drive that is used solely to back up my Mac. If I were to buy another Mac would need a spate external hard drive for each one? Thanks in advance for your help.