HP d212 User manual

GPT hard Disk Drives
For HP Desktops
April 2011
Table of Contents:
Abstract..............................................................................................................1
Why GPT?...........................................................................................................1
GPT vs MBR ........................................................................................................2
Bootable vs Data Drives and UEFI BIOS ................................................................4
OS Support .........................................................................................................6
Storage Driver Support........................................................................................6
Imaging Tool Support for GPT..............................................................................7
Drive Encryption..................................................................................................7
Summary............................................................................................................8
For more information ..........................................................................................8
Abstract
In order to be used in a computer system, a hard disk drive (HDD) must first be
partitioned. Partitioning is done at the drive level and for many decades used the
Master Boot Record (MBR) partition method. A new method called GUID Partition
Table (GPT)) is now used for large-capacity drives. GPT allows for volume sizes
much greater than 2.19TB, and therefore must be used on drives larger than the
MBR limit of 2.19TB. This white paper describes the rationale for GPT and the types
of OS, BIOS, driver, and SW tool support needed to successfully implement GPT
drives in desktop systems.
Why GPT?
HDD areal density (bits/sq in) and tracks per inch (TPI) continue to steadily
increase. For 2010, many typical desktop 3.5” hard drives have areal densities
and TPI that permit capacities up to 500GB per platter. In 2011, it is expected that
improvements in areal density and TPI will allow drive manufacturers to begin
shipping drives that have capacities of1TB/platter. At this density, drives of 2TB
and 3TB capacities become more easily producible and hence cheaper and more
widely available.

2
For decades, MBR partitioning was sufficient to support the amount of hard drive
addressing spaces known as Logical Block Addresses (LBAs) that existed on hard
drives. MBR partitioning supported 32-bit addressing and, along with 48-bit LBA
extensions, was able to support drives up to a limit of 2.19TB using standard 512-
byte sectors (or 512-byte sector emulation). However, now that hard drive sizes are
beginning to exceed the 2.19TB limit, a newer approach is needed. GPT
partitioning, which is part of the overall Unified Extensible Firmware Interface (UEFI)
specification, allows for much larger hard drives than with MBR and will also allow
such a drive to be bootable in a system with UEFI BIOS and UEFI-aware OS.
GPT vs MBR
There are a number of differences between MBR and GPT. Some of the key
differences include the following:
•MBR only supports 4 primary partition table entries while GPT supports 128
primary partitions with current Microsoft Windows™ operating systems.
•MBR uses 32-bit values to indicate the starting offset and length of a partition.
Assuming 512 byte sectors or 512 byte sector emulation, this means an MBR
disk supports 2^32 bit LBAs multiplied by 512 bytes/sectors = 2.19 x10^12
bytes = 2.19TB maximum disk size.
•Since GPT uses 64-bit values to indicate the starting offset and length of a
partition, a GPT disk can theoretically support up to 2^64 LBAs. Assuming 512
byte sectors or 512 byte sector emulation, this means the maximum capacity of
a GPT disk = 9.4 x 10^21 bytes = 9.4 zettabytes (ZB). Microsoft Windows™
file systems design currently limits this to 256TB per drive
•GPT provides redundancy by writing the GPT header and partition table at the
beginning of the disk and also at the end of the disk. If the original GPT
header and partition table gets deleted or corrupted, the backup header and
partition table can be used to help restore the drive. The contents of the GPT
header and partition table are also verified via a CRC32 checksum for the
header and one for the partition table.
Figure 1 on the following page shows a diagram of the GPT Partition Table and
drive layout.

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Figure 1. GPT partition table scheme
Figure 2 on the following page shows a comparison of the MBR and GPT layouts.
Protective MBR
Primary GPT Header
Entries 1 thru 4
Entries 5 – 128
Partition 1
Partition 2
Remaining Partitions
Entries 1 thru 4
Entries 5 – 128
Secondary GPT Header
Protects MBR-based
disk utilities
from overwriting
GPT drives
Defines usable
blocks on the disk
List of drive
partition entries
(up to 128)
Drive partitions
(up to 128)
Secondary/backup
GPT header and
partition entries
LBA = 512 bytes
NOTE: LBA -34 refers to the 34th addressable block
address counted backwards from the last LBA on
the drive.
Primary GPT
Secondary GPT
LBA 0
LBA 1
LBA 2
LBA 3
LBA -34
LBA 34
LBA -33
LBA -2
LBA -1

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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
a non-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.
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
Master Boot Record
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
Protective MBR
Partition Table
Extended
Partition
Primary GUID
Partition Entry
Array
Backup GUID
Partition Entry
Array
Basic GPT Disk LayoutBasic MBR Disk Layout

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The BIOS Characteristic Extension Byte #2 is described in Table 1. Bit 3 of Byte 2
specifies UEFI specification support.
Table 1. BIOS Characteristics Extension Byte 2
Bit Position Description
0 When set, BIOS boot specification is supported
1 When set, function key-initiated Network Service boot is supported. When
function key-initiated Network Service boot is not supported, a network
option ROM may choose to offer this functionality on its own, thus offering
this capability to legacy systems. When the function is supported, the
network adapter option ROM shall not offer this capability.
2 When set, enables Targeted Content Distribution. The manufacturer has
ensured that the SMBIOS data is useful in identifying the computer for
targeted delivery of model-specific software and firmware content through
third-party content distribution services.
3 When set, UEFI specification is supported.
4 When set, the SMBIOS table describes a virtual machine. When cleared, no
inference can be made about the virtuality of the system.
5:7 Reserved for future assignment by this specification.
The user can determine if the system has a UEFI BIOS by looking for the splash
screen during boot referencing a top-level Startup menu (Figure 3).
Figure 3. Splash screen of HP UEFI BIOS system
The startup menu (Figure 4) can be accessed by pressing the Esc key during the
boot sequence.

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Figure 4. Startup Menu
OS Support
32-bit Microsoft Windows™ will not provide boot support for GPT. For HP desktops,
bootable GPT drives and data storage drives will be initially supported under the
Microsoft Windows 7™ SP1 64-bit OS. Bootable GPT drives can also be supported
under the Microsoft Vista™ SP1 64-bit OS. Both of these operating systems require
a UEFI BIOS to support a bootable GPT drive. Data storage-only GPT drives will be
supported under 32-bit and 64-bit Microsoft Windows 7™ SP1 and can be
supported under 32-bit and 64-bit Microsoft Windows Vista™. At this time, there
are no immediate plans for HP Desktops to directly support GPT drives under
Linux™ (HP Workstations have separate OS plans). Table 2 summarizes current OS
support for HP Desktops.
Table 2. Summary of OS support for GPT drives by HP Desktops
Operating system GPT Boot Support? GPT Data Storage Support?
Windows 7™ SP1 64-bit Yes (requires UEFI BIOS) Yes
Windows 7™ SP1 32-bit No Yes
Windows Vista™ SP1 64-bit Yes (requires UEFI BIOS) Yes
Windows Vista™ SP1 32-bit No Yes
Linux™ No direct support from HP No direct support from HP
Storage Driver Support
Since GPT drives have capacities beyond 2.2TB, support is required through
updated storage drivers. Storage driver support can be provided with certain newer
operating systems’ AHCI (Advanced Host Controller Interface) drivers for larger
drive capacities. For improved performance, HP Desktops support GPT hard drives
with storage device drivers from AMD™ and Intel™. These drivers will support both
single drive implementation in AHCI and RAID 0 (striped) and RAID 1 (mirrored)
formats. Expected timeframe for AHCI support is 1H 2011. Support for GPT drives
in bootable RAID configurations is expected in 2H 2011.

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Imaging Tool Support for GPT
In generating SW boot images for GPT drives, the user must utilize “GPT aware”
software tools. Not all tools will automatically support partitioning and formatting
for GPT. For example, only newer versions of Symantec GHOST™ are able to
handle GPT partition tables. The user will need to check the particular tool
documentation to ensure the software provides support for GPT.
A certain percentage of users may choose to re-install the 64-bit OS with a
Microsoft DVD. On machines with UEFI BIOS, the DVD setup utility may try to install
the image in GPT format by default. If this is not what the user wants, then the DVD
setup utility will need to be manually selected to install in MBR format instead. To
install in MBR mode, the user will need to access the boot menu using F9, then
select “Legacy Boot Sources/ATAPI DVD Drive/SATA0” as shown in Figure 5.
Figure 5. BIOs menu of HP UEFI BIOS system
Drive Encryption
For Opal-based SED (Self Encrypting Drive) hard drives, UEFI protocol definitions
and usage for SED are part of the UEFI v2.3.1 Spec published in Feb 2011. To
ensure proper operation of Opal-based SED drives with GPT formatting, users will
need to useUEFI BIOS and SED drives that conform to this version or to later
versions of the UEFI specification. For all types of SED drives, the only other major
requirement is that the “Shadow MBR” used in SED drives must not exceed 128MB.
Since the GPT partition table is normally 15KB, this should not present a problem.
Other drive encryption tools, such as McAfee Endpoint™ software encryption tools,
may or may not have specific GPT support at this point. Consult the particular
software vendor for details regarding planned GPT support.

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Summary
GPT-based hard disk drives offer a more consistent, scalable approach to
formatting and partitioning hard drives. GPT allows more efficient use of the larger
hard drives now becoming available, and also allows such hard drives to be a
bootable part of a UEFI-based system. With GPT, partition and formatting support
of ever-increasing drive sizes is assured for many more years.
For more information
Additional information on topics mentioned in this document is available at the
following websites:
For the UEFI specification, go to the UEFI SIG website at:
http://www.uefi.org/home/
© 2011 Hewlett-Packard Development Company, L.P. The information contained herein
is subject to change without notice. The only warranties for HP products and services
are set forth in the express warranty statements accompanying such products and
services. Nothing herein should be construed as constituting an additional warranty. HP
shall not be liable for technical or editorial errors or omissions contained herein. Intel is
a trademark of Intel Corporation in the U.S. and other countries. Microsoft and
Windows are U.S. registered trademarks of Microsoft Corporation. Microsoft and
Windows are U.S. registered trademarks of Microsoft Corporation.
660177--001, April 2011