When you buy a new Mac laptop, iMac, or Mac mini, the internal startup hard drive is set up with one partition—that is, one large section of storage space. You can use Disk Utility to partition the startup drive (create smaller storage sections), even while the startup drive is being used to boot your Mac. Partitions can help organize your data.
But before you do so, it would be wise to back up your data on the startup drive by copying it to another drive. Disk Utility won’t erase the data, but it doesn’t hurt to be prepared if problems occur.
This example will add a partition on the startup drive of a MacBook Pro. When the process is done, the two partitions will appear on the Mac desktop as two hard drive icons. (We also have details on how to partition an external hard drive.)