An external drive can will allow you keep extra copies of important files and can be used to quickly move large files between computers. If you need to use your external drive to move files between Macs and Windows PCs you’ll need to use a filesystem that both platforms can read.
There are free and paid third party applications that can be used to allow Windows to read Mac formatted drives and there are similar applications available for both platforms that will allow a Mac to read Windows native formatted drives, but these are often slow, buggy and/or expensive or you may not have permission to install these on the computer. Luckily, both the Mac OS and Windows OS allow you to format drives that will be compatible with either Operating System Platform.
WARNING: Following this guide will require you to re-format your external drive which WILL ERASE ALL DATA FROM YOUR DRIVE. MAKE A BACKUP COPY OF FILES YOU DON’T WANT TO LOSE BEFORE YOU START.
Option 1: FAT
Pros: Works natively with all Macs and Windows PCs
Cons: Can’t handle files larger than 4GB in size.
How to format using FAT (from a Mac):
1. Open Disk Utility on your Mac. (You can open it from the Applications/Utilities folder or quickly with Spotlight, click on the Magnifying glass and start typing Disk Utility.)
2. Select the drive you wish to format.
3. Select the “Erase” tab in Disk Utility.
4. Select MS-DOS (FAT) from the drop down box.
6. Let it finish, and you’re done.
Option 2: exFAT
Pros: Can work with large files
Cons: Not compatible with older operating systems. You must have Mac OS X 10.6.5 or newer, and PCs need to be Windows Vista SP1, Windows 7, Windows 8 or newer.
How to format using exFAT (from Mac): To format the drive from a Mac, you must use Mac OS X 10.7 (Lion) or 10.8 (Mountain Lion) [as of this posting – Spring 2013, the school computers are on Snow Leopard – 10.6.8, so you’ll need to use the Windows instructions below if you don’t have access to a computer with Lion or Mountain Lion]. Follow the steps for FAT above, but substitute exFAT for MS-DOS (FAT) in step 4.
Otherwise, you’ll need to format the drive from Windows.
How to format using exFAT (from Windows):
1. Plug the disk into a Windows Vista SP1 or Windows 7 computer.
2. Open the Computer window.
3. Right click on the drive, and select Format.
4. Select exFAT from the drop down box, and click on Start.
5. Done! Now this drive will work with Macs and PCs.
Although FAT is more compatible with older systems, the maximum 4GB filesize is very limiting. You would not be able to use this disk for long HD videos and large disk images, for example. For this reason, exFAT is recommended.
(Source images and document format from www.mactip.net.)