Annex A (Informative) Hybrid Mbr Boot; Hybrid Mbr Boot Overview; Gpt Support For Hybrid Mbr Boot Code; Table A.1 - Protective Mbr With Hybrid Mbr Boot Code - Western Digital T13/2132-D User Manual

June 23, 2010
A.1 Hybrid MBR boot overview
This annex describes how MBR boot code called hybrid MBR boot code may be constructed to support a GPT
disk layout (see UEFI-2.3) in a legacy BIOS system.
A.2 GPT support for hybrid MBR boot code
When using hybrid MBR boot code, the GPT disk layout includes one GPT partition with the Legacy BIOS
Bootable bit set to one in the Attributes field (see UEFI-2.3).
The Protective MBR defined in UEFI-2.3 is modified as shown in table A.1 to include hybrid MBR boot code.
Mnemonic Byte Offset
Boot Code
Unique MBR Disk Signature
Unknown
Partition Record
Signature
Reserved
Figure A.1 shows an example of a GPT disk layout with hybrid MBR boot code.
Primary
Protective
GPT
MBR with
hybrid
MBR boot
code
LBA 0 LBA 1
Figure A.1 — GPT disk layout with hybrid MBR boot code example
Working Draft Enhanced Disk Drive - 4 (EDD-4)
(informative)
Hybrid MBR boot
Table A.1 — Protective MBR with hybrid MBR boot code
0
440
444
446
510
512 Logical Block Size - 512 See UEFI-2.3
UEFI
system Partition
partition
Annex A
Byte Length Contents
440 Hybrid MBR boot code (see A.3)
4 See UEFI-2.3
2 See UEFI-2.3
16 * 4 See UEFI-2.3
2 See UEFI-2.3
Partition
GPT Protective partition
T13/2132-D Revision 3
Backup
Partition
GPT
End of disk
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