Western-digital T13/2132-D User Manual download pdf (Page 83)

June 23, 2010 T13/2132-D Revision 3

Working Draft Enhanced Disk Drive - 4 (EDD-4) 71

Annex A

(informative)

Hybrid MBR boot

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.

Figure A.1 shows an example of a GPT disk layout with hybrid MBR boot code.

Figure A.1 — GPT disk layout with hybrid MBR boot code example

Table A.1 — Protective MBR with hybrid MBR boot code

Mnemonic Byte Offset Byte Length Contents

Boot Code 0 440 Hybrid MBR boot code (see A.3)

Unique MBR Disk Signature 440 4 See UEFI-2.3

Unknown 444 2 See UEFI-2.3

Partition Record 446 16 * 4 See UEFI-2.3

Signature 510 2 See UEFI-2.3

Reserved 512 Logical Block Size - 512 See UEFI-2.3

Protective

MBR with

hybrid

MBR boot

code

Primary

GPT

UEFI

system

partition

Partition Partition

Backup

GPT

Partition

GPT Protective partition

LBA 0 LBA 1 End of disk

1 2 ... 78 79 80 81 82 83 84 85 86

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Western-digital T13/2132-D User Manual Page 83