On Jan 29, 2013, at 1:41 AM, Manivannan Chithiresan <[email protected]>
wrote:
> Hi,
>
> When the OSType field of Legacy MBR Partition record is set as 0xEF (uEFI
> system partition)? What is the scenario it is set and when it will be useful ?
The Master Boot Record OSType (or partition type) is used to describe how the
partition is used. It could for example be used by a disk utility to show the
user what a partition contains or what it is used for. A value of 0xEF means
the partition is an EFI system partition and contains a FAT12, FAT16, or FAT32
file system. The 1st stage UEFI OS loader resides on the EFI System Partition
at a location stored in NVRAM by the OS installer. In uEFI the OS loader is an
EFI application that gets loaded from disk. On a legacy boot the BIOS will load
the boot strap code in the MBR and jump to it. This boot strap code will load
the first 512 bytes of the partition that is marked as bootable and jump to
that real mode code. The 0xEF value also allows building an MBR partitioned
disk that can boot both legacy and uEFI from the same media.
The OSType 0xEE is used if the disk is partitioned for GPT. The idea was, at
least in the early days, that if a disk utility did not understand GPT and only
knew about MBR the 0xEE would imply that the disk had real data on it and thus
it would dangerous to erase it.
The interesting thing about the OSType field is in the early days people just
grabbed numbers so some of the lower numbers imply multiple things. There is
also no standard list of what the numbers mean. When we investigated this for
the EFI specification we found the de facto list was maintained by a person who
lived in Scandinavia as a hobby.
Thanks,
Andrew Fish
>
> Regards,
> Mani.
>
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