Apple Partition Types: How and When to Use Them

Understanding partition schemes for your Mac

Partition types, or as Apple refers to them, partition schemes, define how the partition map is organized on a hard drive. Apple directly supports three different partition schemes: GUID (Globally Unique IDentifier) Partition Table, Apple Partition Map, and Master Boot Record. With three different partition maps available, which one should you use when you format or partition a hard drive?

Disk utility partition panel
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Understanding Partition Schemes

GUID Partition Table: Used for startup and non-startup disks with any Mac computer that has an Intel processor. Requires OS X 10.4 or later.

Intel-based Macs can only boot from drives that use the GUID Partition Table.

PowerPC based Macs that are running OS X 10.4 or later can mount and use a drive formatted with the GUID Partition Table, but cannot boot from the device.

Apple Partition Map: Used for startup and non-startup disks with any PowerPC-based Mac.

Intel-based Macs can mount and use a drive formatted with the Apple Partition Map, but cannot boot from the device.

PowerPC-based Macs can both mount and use a drive formatted with the Apple Partition Map, and can also use it as a startup device.

Master Boot Record (MBR): Used for starting up DOS and Windows computers. Can also be used for devices that require DOS or Windows compatible file formats. One example is a memory card used by a digital camera.

Selecting and Changing the Partition Scheme

Changing the partition scheme requires reformatting the drive. All data on the drive will be lost in the process. Be sure and have a recent backup available so you can restore your data if needed.

  1. Launch Disk Utilities, located at /Applications/Utilities/.

  2. In the list of devices, select the hard drive or device whose partition scheme you wish to change. Be sure to select the device and not any of the underlying partitions that may be listed.

  3. Click the Partition tab.

  4. Disk Utility will display the volume scheme currently in use.

  5. Use the Volume Scheme drop-down menu to select one of the available schemes.

    Please note: This is the volume scheme, not the partition scheme. This drop-down menu is used to select the number of volumes (partitions) you want to create on the drive. Even if the currently displayed volume scheme is the same as what you wish to use, you must still make a selection from the drop-down menu.

  6. Click the Option button. The Option button will only be highlighted if you chose a volume scheme. If the button isn't highlighted, you need to go back to the previous step and choose a volume scheme.

  7. From the list of available partition schemes (GUID Partition Scheme, Apple Partition Map, Master Boot Record), select the partition scheme you wish to use, and click OK.

To complete the formatting/partitioning process, take a look at Disk Utility: Partition Your Hard Drive With Disk Utility.