The second is the more familiar Macintosh HD. The first is hidden and named Recovery HD for OS X Recovery, allowing you to reinstall OS X without needing any physical media. With the introduction of OS X Lion, your Mac's hard disk is split into two partitions with two corresponding volumes. Formatting a disk partition is no different than deciding which room will be the bedroom or kitchen. The more walls you put up, the more rooms you'll have, but all limited to the total amount of space you first had available.īut these rooms can't be used yet, not until you decide what each room will be. Think of partitioning as putting up dividing walls to create additional rooms. Imagine you have a loft apartment that's just four outer walls. Here's a USB hard drive that has been split into 16 partitions, all of which will display separately on the Mac as separate volumes since they've been formatted, though they are all on the same drive. Once a partition has been formatted, this combination of partition and filesystem is known as a volume. In order to store data on a partition, it needs a filesystem. A hard disk can contain a single partition, making use of all the space it contains, or it can be split into multiple partitions.

TerminologyĪ partition is a logical storage unit located on a hard disk. The following guide will require the use of an external hard drive which will be erased and partitioned. In this series, we'll look at how to replicate the functionality of Disk Utility at the command-line. It's a simple way of interacting with attached storage on your Mac.īeyond this graphical front-end are some powerful command-line tools that we can use directly. Disk Utility within Mac OS X provides a range of disk management tools, from erasing and repartitioning hard disks to restoring images and repairing volumes.

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