When you buy a new hard drive, your first impulse may be to connect it to your Mac and start copying files to the new drive. But with all that new storage space it might make sense to partition the hard drive.
When you partition, you are dividing the hard drive’s storage space into sections. For example, you can partition a 1TB hard drive into two 500GB sections. Each section would appear on your Mac’s desktop like a single hard drive would.
Partitioning can help organize your data. You can create a partition that stores just the documents you create, or dedicate a partition to storing your iTunes media.
This tutorial goes through the steps of partitioning an empty external hard drive using Disk Utility, which comes with every Mac. The steps here are using Mac OS X 10.6.7 and should be similar for older OS versions.
We have a separate tutorial on how to partition the startup drive while it's being used to boot your Mac. That tutorial can also be used to partition an external hard drive that has data on it.