Intel Extensible Firmware Interface, Specification

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File System Format
Version 1.02 12/12/00 315
Table 16-5. Legacy Master Boot Record
Mnemonic
Byte
Offset Byte
Length
Description
BootCode 0 440 Code used on legacy Intel architecture system to select
a partition record and load the first block (sector) of the
partition pointed to by the partition record. This code is
not executed on EFI systems.
UniqueMBRSignature 440 4 Unique Disk Signature, this is an optional feature and
not on all hard drives. This value is always written by
the OS and is never written by EFI firmware.
Unknown 444 2 Unknown
PartitionRecord 446 16*4 Array of four MBR partition records.
Signature 510 2 Must be 0xaa55.
The MBR contains four partition records that define the beginning and ending LBA addresses that a
partition consumes on a hard disk. The partition record contains a legacy Cylinder Head Sector
(CHS) address that is not used in EFI. EFI utilizes the starting LBA entry to define the starting
LBA of the partition on the disk. The size of the partition is defined by the size in LBA field.
The boot indicator field is not used by EFI firmware. The operating system indicator value of 0xEF
defines a partition that contains an EFI file system. The other values of the system indicator are not
defined by this specification. If an MBR partition has an operating system indicator value of 0xEF,
then the firmware must add the EFI System Partiiton GUID to the handle for the MBR partition
using
InstallProtocolInterface()
. This will allow drivers and applications, including
OS loaders, to easily search for handles that represent EFI System Partitions.
Table 16-6. Legacy Master Boot Record Partition Record
Mnemonic
Byte
Offset Byte
Length
Description
Boot Indicator 0 1 Not used by EFI firmware. Set to 0x80 to indicate that this is
the bootable legacy partition.
Start Head 1 1 Start of partition in CHS address, not used by EFI firmware.
Start Sector 2 1 Start of partition in CHS address, not used by EFI firmware.
Start Track 3 1 Start of partition in CHS address, not used by EFI firmware.
OS Type 4 1 OS type. A value of 0xEF defines an EFI system partition.
Other values are reserved for legacy operating systems, and
allocated independently of the EFI specification.
End head 5 1 End of partition in CHS address, not used by EFI firmware.
End Sector 6 1 End of partition in CHS address, not used by EFI firmware.
continued