| Master Boot Record | |
Partition Table |
|
| | |
| | |
Partition
Extended
Basic MBR Disk Layout
Master Boot Code
1st Partition Table Entry
2nd Partition Table Entry
3rd Partition Table Entry
4th Partition Table Entry
0x55 AA
Primary Partition (C:)
Primary Partition (E:)
Primary Partition (F:)
Logical Drive (G:)
Logical Drive (H:)
Logical Drive n
Basic GPT Disk Layout
Master Boot Code
1st Partition Table Entry
2nd Partition Table Entry
3rd Partition Table Entry
4th Partition Table Entry
0x55 AA
Primary GUID Partition
Table Header
GUID Partition Entry 1
GUID Partition Entry 2
GUID Partition Entry n
GUID Partition Entry 128
Primary Partition (C:)
Primary Partition (E:)
Primary Partition n
GUID Partition Entry 1
GUID Partition Entry 2
GUID Partition Entry n
GUID Partition Entry 128
Backup GUID
Partition Table Header
MBR Protective
GUID Primary
Entry Partition
Array
GUID Backup
Entry Partition
Array
Figure 2. Comparison of MBR and GPT disk layouts
Bootable vs Data Drives and UEFI BIOS
Since the partitions on a data-storage drive are accessed by the OS and not the BIOS, GPT drives can be used on non-UEFI systems as data-storage drives. These drives cannot, however, be used as boot drives in such systems. The legacy BIOS in
anon-UEFI system cannot find the boot information on a GPT-formatted drive and therefore cannot complete the boot process into the OS. In using a GPT drive as a data-storage drive, the drive must be formatted using tools that can create GPT partitions.
In order to boot from a GPT-formatted drive, the system must have a UEFI BIOS. UEFI understands how to find the boot information on a GPT drive. In addition, the system must also have a “UEFI aware” OS such as Microsoft Windows 7 ™64-bit. For selected desktops, HP implements the Type 0 BIOS Information data structure (as described in version 2.7 of the SMBIOS specification) to indicate UEFI BIOS support. The BIOS Characteristics Extension Bytes field within this structure has defined a bit that, if set, identifies the system as UEFI compliant. Table 1 describes BIOS Characteristic Extension Byte 2, with Bit 3 identified as the bit for UEFI specification support.
