Plug the external hard drive into the computer. Select the Applications folder from the Dock or the Finder window. Within that folder select the Utilities folder and then select the Disk Utility application from there.
The Disk Utility window will now open. In this window, double click the name of the attached external hard drive, which will appear in the list of memory locations and partitions at the left of the window.
Now, click on the Partition tab at the top of the window. Be sure to locate the Volume Scheme: label at the left of all of the information. Underneath this label are options for how you want your hard drive partitioned and a diagram showing the current scheme.
In the Partition screen, first select 3 Partitions from the options under the Volume Scheme: label at the left of the window.
Now, using the diagram of your current partition scheme shown under the Volume Scheme: label, select the top partition, which should be labeled Untitled 1 by default. This is the partition of your hard drive you will format to work with a Mac. It's a good idea to change the name of this partition to something that will remind you that this is the area that is formatted for a Mac. You can change the name under the Volume Information label. Also under this label is the Format: option, which you can leave the default since this partition is being formatted for a Mac.
Next, select the second partition down. This partition will be formatted as FAT-32, which is a format with a limited transfer size however it will work on both OS platforms. This is the partition you will use for transferring information between the Mac and PC partitions. As before, give this partition a name, but this time select the drop-down menu next to the Format: label, and select MS-DOS (FAT).
Now, select the third partition. This one will eventually be formatted to work with a PC, but we can't perform that action on a mac. So for now, just give this partition a name to help you remember this is the one you will format for PC use, and then change the Format: option to Free Space.
Now your window should look something like this. Notice that in this example the sizes are left to their default. If you wish to change the sizes of your partitions, do this under the Size: option that is under the Volume Information label right below Format. Keep in mind that your FAT-32 partition will ideally only be used for transfering information, so it wouldn't hurt to make that a smaller size, somewhere between 25 to 50 GB will probably do just fine. When all your information is set, click Apply.
A dialog box will pop up, asking if you wish to use either of the partitions available to back up your computer with Time Machine. It is up to you whether or not you want to back-up your machine, but for this tutorial go ahead and click Don't Use. After you click Don't Use, your hard drive will be formatted, and you will be notified when it is finished formatting. You will now be able to transfer files to the Mac and FAT-32 partitions on the drive. When you are ready, attach your drive to a PC, and continue reading to finish the formatting process.
Now you have to format the last partition of the hard drive to work with a PC. This is done essentially the same way as formatting the entire hard drive to work with a PC; however there is one key change which is highlighted below and on the Formatting for Primarily PC Users page. If you are unfamiliar with how to format the hard drive to work with a PC, please go to the linked page.
(Partitioned Hard Drive) Here is what the partitioned hard drive will look something like, and the section you should select is highlighted.
Once you've finished formatting the partition which will be used with a PC, you have successfully formatted your Hard Drive to work with both Platforms. Remember that if you have any questions or issues, please contact the interns at the MPC desk for assistance.