Question: are all external hard drives compatible with mac?
Answer: Any external hard drive will work with PCs or Macs, as long as the connectors are there (Firewire, USB, etc.) It doesn't matter how the drive is formatted out of the box, since you can re-format any way you like. Formatting in HFS (Mac OS Extended) or FAT32 or NTFS-3G can be done with the Mac OS X Disk Utility.