It can easily do this: Partition the drive, one for your Mac and one for your PC. The respective machines should easily recognize the drive and cooperate; however, there are numerous programs abounding that enable users to format the drive such that it doesn't require partitioning but can still read and write files to both operating systems (i.e. Windows and and OS X). I'm partial to partitioning, even more so to having dedicated drives (one for PCs, one for Macs). But, yes, it can be formatted and partitioned to back up both.