Thursday, June 26, 2008

What is MBR and GPT?

If you have encountered a disk problem in hackintosh then, you might came across the terms MBR which is an acronyms for Master Boot Recored and GPT which is an acronyms for GUID Partition Table.

every hard drive is separated into partitions, even if it has only one partition it has a table describing that mapping, that mapping contains data like: how many partition on the drive, what is the size of each partition, what is the starting address of each partition etc. the partition table info can be described in two manners (actually more but we are interested only in these two), the one is MBR and the other is GUID, this manner is named Partition Scheme.

the partition schemes differ from one another by the way it holds the addressing of the partitions (CHS vs LBA), and by the max size they support for each partition, where is the boot recored kept etc. MBR is used in PC that uses a BIOS, GUID is used in computers that support EFI (like Mac). you can read more about it here.

when you install a hackintosh you need to prepare a partition for OSX, if it is a new partition on existing (already partitioned, from windows) disk, then there is no doubt you have an MBR partition scheme (well 99%), but if you prepare the disk from the OSX installation using the Disk Utility, then you have an option to choose from 3 types (MBR, GUID, Apple Partition Table Scheme).

Note 1: Apple Partition Table is not good scheme for a bootable HD for hackintosh, it is mostly for PPC.
Note 2: if you choose to repartition your hard drive from the Disk Utility or any other tool, it will cause loss of all information on that hard drive (including any Windows flavor you have installed on it).

you can repartition your hard drive from leopard installation or existing leopard installation in this way:
open Disk Utility.
right click on the drive you wish to partition from the left hard-drive tree, and choose the "Partition" option.

from the "Volume Scheme" drop-down menu choose the number of partitions you would like to create on the disk.

from the lower "Options..." button choose the desired partition scheme, i would suggest MBR.

if you would like just to know what partition you are currently using then open "Disk Utility".
and from the left hard-drive tree choose the drive you wish to query, (Note: the drive and not its partitions)

then look at the right lower corner next to the label: "Partition Map Scheme" and you will see your partition scheme (Master Boot or GUID)


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