Windows and Mac computers use different hard drive formats, but in most cases they support sharing external storage. For a Windows partition installed on a Mac via Boot Camp, Apple provides compatibility drivers so that you can access OS X volumes from Windows.
Compatible Hard Drive Format
OS X and Windows include native support for FAT32 file systems, so if you're sharing an external hard drive between a Mac and PC, format it with FAT32. However, if your drive is larger than 2TB and you plan to store files larger than 4GB, use exFAT instead. OS X 10.6.5 and later support exFAT, as does Windows XP SP3 and later. Mac computer require additional drivers to write to the native Windows file system, NTFS, and PCs need extra drivers to work with the native Mac file system, HFS+.
Sharing Boot Camp Partitions
When you install Windows on a Mac using Boot Camp, the Windows partition is formatted using NTFS. To access OS X files from Windows, download the Boot Camp support software, copy it to a FAT-formatted flash drive and double-click the installer file from within Windows (link in Resources). Whether you boot into OS X or Windows, you can copy files from, but not write files to, the other partition. To choose a boot partition at startup, hold down the "Option" key when you turn on your Mac.
