On a recent episode of Mac Power Users I mentioned a tip where I dual formatted a flash drive to have both Mac OS Extended and MS-DOS (FAT) partitions. The idea behind this is it allows me to use this flash drive natively with Macs and Windows machines. A few people have asked how I did this. It's actually quite easy using Disk Utility. This example shows the formatting of a USB flash drive, but the same process works with any other hard drive.
Open Disk Utility
Insert the media you want to format and open Disk Utility. By default Disk Utility is located inside the Utilities Folder inside your Applications Folder. Locate the drive you want to dual format. In this case, I want to format the 8GB SanDIsk Cruzer Flash Drive.
1. Highlight the Main Volume of the Drive (the upper volume)
2. Select Partition
Create 2 Partitions
In the partition window, you'll want to change the layout of the drive to create 2 (or however many you choose) partitions.
WARNING - PARTITIONING THE DRIVE WILL ERASE ALL DATA!
Choose the Format of the Partitions
Once you have the desired number of partitions created, you can choose the formats of the partitions. For the partitions you intend to use for PCs I recommend selecting "MS-DOS (FAT)" and for the partition you plan to use for the Mac I recommend "Mac OS Extended (Journaled)"
Note: Some PC operating systems will only see the first partition on a drive. Therefore I recommend you make the PC partition the first one.
Adjust the Size of the Partitions
You can adjust the size of the respective partitions. You may want them equal size or you may want one partition larger than the other. You can adjust the size of the partitions either by clicking on a partition and typing the desired size in the size box or moving the slider between the two partitions.
Name Your Partitions
Give each partition a unique and memorable name.
You can optionally choose a partition scheme for each partition. Generally this will be selected for you by default. You'll likely want to use GUID Partition Table with your Mac Partitions and Master Boot Record for your PC Partitions
Apply Your New Partition Scheme
Double check your selections and make absolutely sure you've backed up all the data on your drive. Once you click Apply all the data on your drive will be erased and the new partition scheme will be created. You'll then be left with a clean disk with separate partitions ready for the Mac and PC.
Read the warning dialogue that pops up and if you're ready to proceed, click Partition.