Formatting new external hard drives for use with both Mac and Windows computers*

Most external hard drives can be used on both Windows and Mac OSX. This is useful if a drive is being used under both Operating System (OS) to move files between the two environments. Most new drives come formatted in the NTFS (Windows) or HFS+ (Mac) format.

For a hard drive to be able to be read and written to in both a PC and Mac computer, it must be formatted to exFAT or FAT32 file format. FAT32 has several limitations, including a 4 GB per-file limit. This is a file system limitation that affects both Mac's and PC's, and the only workaround is to format the drive to exFAT.

The easiest way to format the drive to FAT32 or exFAT is by using Mac OSX's built-in Disk Utility for FAT32, or both Mac OSX and Windows' built-in tools, Disk Utility or Disk Management respectively for exFAT.

If you work exclusively in either the Mac or in the Windows environment, there's no need to reformat your hard drive to accommodate the other platform.
 

*Text originally from the web site of Western Digital, makers of external hard drives. More information can be found at their site.