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If you need to use big, over 2 GB files both in Windows and Mac OS X’s, MBR partition format and exFAT file system could be the most practical option for your mobile HDD.
However, note that there have been reliability problems with exFAT in hard use. Always keep a backup on a trusted media.
Mac OS X’s Disk Utility is easy, but what to do if you have to quickly reformat an GPT/EFI disk (from Mac or Win 7) to MBR partition layaout and exFAT file system in Windows 7 or XP ?
Let’s assume the external hard disk is Disk 3 (check with Computer -> Manage -> Storage -> Disk Management) and the drive letter is G:
2) In Windows 7, Choose Start -> All Programs -> Accessories -> Command Prompt -> Right-click & choose “Run as administrator”
In Windows XP, use Windows-R and cmd — for exFat support you have to install a patch first: http://support.microsoft.com/?kbid=955704
3) Type commands
diskpart select Disk 3 clean create partition primary assign letter=g exit format g: /fs:exfat /q exit