Thread: Frequently asked questions about the GUID Partitioning Table disk architecture

Summary

Here frequently asked questions about GUID Partition Table disk architecture are explained.

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What is a GUID Partition Table disk?

The GUID Partition Table disk design was launched as part of Extensible Firmware Interface initiative. GUID Partition Table is a new disk design that increases on older Master Boot Record (MBR) partitioning method that has been general to Intel-based PCs.

A partition is a adjacent space of storage on a physical or logical disk that works as though it were a separate disk. Partitions are able to be seen to the system firmware and installed operating systems. Access to a partition is controlled by system firmware and operating system that is presently active.

Why do we need GUID Partition Table? GUID Partition Table disks can develop to a very big size. As of July 2001, the Microsoft execution supports a hard disk of up to 18 EB (512 KB LBAs).There are many partitions on a GUID Partition Table disk is not controlled by temporary plans such as container partitions as defined by MBR Extended Boot Record. The Microsoft execution of GUID Partition Table is limited to 128 partitions. Though, it is key to note that one partition is used for EFI System Partition, one for Microsoft Reserved and two more are used if you use dynamic disks. This leaves 124 partitions for data use. The GUID Partition Table disk partition design is well described and totally self-identifying. Data that is critical to operating system is placed in partitions and not in unpartitioned or "hidden" sectors. It does not allow for hidden sectors or partitions. It uses primary and backup partition tables for redundancy and CRC32 fields for developed partition data structure reliability. The GUID Partition Table uses version number and size fields for future expansion. It has a unique identification GUID and a partition content type, so no coordination is necessary to prevent partition identifier collision. Every GUID Partition Table partition has a 36-character Unicode name, which means that any software can present an easily readable name for partition without any extra understanding of the partition.

MBR disks maintain only four primary partitions table entries or many logical partitions in the total partition. If you want more partitions, then extended partition is necessary. Then it can be subdivided into one or more logical disk. Only single partition there on given drive, and maximum number of logical drives is MAXULONG/4.All MBR disk partitions and logical drives have to be cylinder-aligned, even on hardware RAID sets that are made from many unlike drives with no obvious physical geometry. MBR partitioning rules are difficult and badly specified.Another common practice is to use partitioned or "hidden" sectors to hold specific information. That practice is undocumented and results in severe system problems that are difficult to correct. Many years, broken executions and tools have been released to the public, making support difficult.

Is Extensible Firmware Interface required for a GUID Partition Table disk?

No. GUID Partition Table disks are self-identifying. All data that is necessary to read the partitioning system of a GUID Partition Table disk is fully contained in designs in particular place on physical media.

Is Extensible Firmware Interface required for a GUID Partition Table disk?
No. GUID Partition Table disks are self-identifying. All data that is necessary to read the partitioning system of a GUID Partition Table disk is fully contained in designs in particular place on physical media.

How big can a GUID Partition Table disk be?

In theory, a GUID Partition Table disk can be up to 264 sectors in a single logical block in length. Logical blocks are commonly 512 bytes or one sector in size. In practice, Windows XP maintains GUID Partition Table disks of up to around 18 exabytes in size.

How many partitions can a GUID Partition Table disk have?

In theory, an unlimited number. As the July 2001, the Microsoft execution is 128 partitions. The number of partitions is limited by the amount of space that is kept for making partition entries.

Can a disk be both a GUID Partition Table disk and an MBR disk?

No. Though, all GUID Partition Table disks have a defensive MBR that is used for legacy programs that do not know the GUID Partition Table disk formation.

If this happened, you have to used an MBR-only-aware disk tool to access the GUID Partition Table disk. If the disk is larger than the maximum size an MBR can report, will the entire disk contents be protected?

The EE partition in the Protective MBR is specified to be the maximum size that is allowable in an MBR. Can the 64-bit version of Windows XP read, write, and boot from

GUID Partition Table disks?

Yes.

Can the 64-bit version of Windows XP read, write, and boot from MBR disks?

The 64-bit version of Windows XP can read and write MBR disks, but cannot boot from MBR disks. Can the 32-bit version of Windows XP read, write, and boot from

GUID Partition Table disks?

No. The 32-bit version will see only the Protective MBR. The EE partition will not be raised or showing to program software.

Can the 32-bit version of Windows XP read, write, and boot from MBR disks?

Yes.

Can Microsoft Windows 2000, Microsoft Windows NT 4.0, or Microsoft Windows 98/95 read, write, and boot from GUID Partition Table?
No. Legacy software will see only Protective MBR.

GUID Partition Table and MBR disks can be clubbed only on 64-bit systems, and limitations apply which are given below:

• The Windows XP loader and the boot partition must exist in a GUID Partition Table disk. Other hard disks can be either MBR or GUID Partition Table.

• Both MBR and GUID Partition Table disks can be there in a single dynamic disk collection. Volume sets can extent both MBR and GUID Partition Table disks, though, the MBR cylinder alignment limit might cause some problems with mirroring or striping MBR and GUID Partition Table disks.

What about removable media?

Removable media must be MBR or "superfloppy."

What is the default behavior of the 64-bit version of Windows XP when partitioning media?

Fixed disks are divided by using GUID Partition Table partitioning. GUID Partition Table disks can be transformed to MBR disks only if all presented partitioning is first deleted, with linked loss of data.

What is the default behavior of the 32-bit version of Windows XP when partitioning media?

Only MBR disks can be used. MBR disks cannot be transformed to GUID Partition Table disks.

There is no natural mapping between drive letter and partition that can be used to decide one from other. A fundamental data partition must be recognized by its partition GUID.

How can an Extensible Firmware Interface System Partition be created?

Extensible Firmware Interface System Partitions can be formed by using the Extensible Firmware Interface firmware utility Diskpart.efi or the Windows XP command-line utility Diskpart.exe, or they can be formed programmatically by using IOCTL_SET_DRIVE_LAYOUT.

What can be changed on a partition?

You should not change any partition header entry openly. Do not use disk tools or utilities to make modifications.

Can there be two Extensible Firmware Interface System Partitions on a single disk?
Such a design should not be formed and will not be maintained.
What about two Extensible Firmware Interface System Partitions on two different disks?
Extensible Firmware Interface System Partitions can be simulated for high-availability configurations. Replication must be done yourself and the contents must be coordinated by yourself. Extensible Firmware Interface System Partitions cannot be mirrored.

What does Microsoft place in the Extensible Firmware Interface System Partition?
Microsoft sets the loader, and other files that are needed to boot the operating system in the Extensible Firmware Interface System Partition.

Why must the Microsoft Reserved Partition be created when the disk is first partitioned?

After the disk is separated, there will be no free space left to make a Microsoft Reserved Partition.

When firstly formed, the size of the Microsoft Reserved Partition depends on the size of the disk drive:

• On drives that are less than 16 GB, the Microsoft Reserved Partition is 32 MB.
• On drives that are greater than or equal to 16 GB, the Microsoft Reserved Partition is 128 MB. As the Microsoft Reserved Partition is divided into other partitions, it becomes smaller.

How is a basic data partition identified?

It has the following partition type GUID:
DEFINE_GUID (PARTITION_BASIC_DATA_GUID, 0xEBD0A0A2L, 0xB9E5, 0x4433, 0x87, 0xC0, 0x68, 0xB6, 0xB7, 0x26, 0x99, 0xC7)

What about dynamic disks?
Dynamic disks use two different GUID Partition Table partitions:
• A data container partition equivalent to the MBR partition 0x42, with this GUID:
DEFINE_GUID (PARTITION_LDM_DATA_GUID, 0xAF9B60A0L, 0x1431, 0x4F62, 0xBC, 0x68, 0x33, 0x11, 0x71, 0x4A, 0x69, 0xAD)

• A partition to contain the dynamic pattern database, with this GUID:
DEFINE_GUID(PARTITION_LDM_METADATA_GUID, 0x5808C8AAL, 0x7E8F, 0x42E0, 0x85, 0xD2, 0xE1, 0xE9, 0x04, 0x34, 0xCF, 0xB3)

How can a specific partition be mounted?

You can access the GUID Partition Table disk partitions of many types by using tools given below.

Diskpart.efi:
Firmware: Extensible Firmware Interface System Partition
Microsoft Reserved Partition

Diskpart.exe:

Windows XP: Extensible Firmware Interface System Partition
Microsoft Reserved Partition

Diskgmt.msc:

Windows XP: Extensible Firmware Interface System Partition
DATA

Explorer.exe:

Windows XP: DATA

What about FTdisk sets?

There is no FTdisk set maintain on Windows XP for MBR or GUID Partition Table disks. The only support for logical volumes is through dynamic disks.
Can a disk be converted from GUID Partition Table to MBR or MBR to GUID Partition Table?

Yes, but only if the disk contains no partitions or volumes. Any data on the disk will be destroyed.