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?
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.
How to select the partition scheme to use when formatting a hard drive or device.
WARNING: Changing the partition scheme requires reformatting the drive. All data on the drive will be lost in the process.
- Launch Disk Utilities, located at /Applications/Utilities/.
- 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.
- Click the 'Partition' tab.
- Disk Utility will display the volume scheme currently in use.
- Use the Volume Scheme dropdown menu to select one of the available schemes. Please note: This is the volume scheme, not the partition scheme. This dropdown 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 dropdown menu.
- 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.
- 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, please see 'Disk Utility: Partition Your Hard Drive With Disk Utility.'