GPT Partition Entry: Structure, Array, and GUID Fields

Q: Is every GPT partition entry exactly 128 bytes?

No. UEFI 2.10 permits entry sizes of 128 × 2^n bytes. The Header's SizeOfPartitionEntry field tells a parser the actual size. Thus, a parser that always jumps forward exactly 128 bytes may read larger entries incorrectly.

29.10.2026 Vasilii

GPT Partition Entry Structure, Array, and GUID Fields

A GPT partition entry is a record that describes one partition on a GUID Partition Table (GPT) disk. It identifies the partition’s type, unique GUID, starting and ending logical block addresses (LBAs), attributes, and name. The usual GPT partition entry structure occupies 128 bytes. By decoding these fields, you can locate a partition, calculate its size, and check whether its metadata makes sense.

This guide follows UEFI Specification 2.10 and uses Windows 10, Windows 11, and Windows Server as practical examples. The underlying GPT format also applies to other compatible operating systems. Every byte example below is synthetic, not a capture from a real disk.

What Is a GPT Partition Entry?

A GPT partition entry defines a partition’s identity and boundaries; it does not contain the partition’s files. To see where it fits, separate three structures:

Estrutura	What it stores
GPT Header	Array location, entry count and size, usable LBA range, and checksums
GPT Partition Entry Array	A sequence of partition records, including unused slots
GPT partition entry	One partition’s GUIDs, boundaries, attributes, and name

The entry directs the operating system to a region of logical blocks. That region may hold NTFS, FAT32, exFAT, another file system, or data without a conventional file system.

For the overall disk layout, see Amagicsoft’s GUID Partition Table (GPT) overview.

GPT Partition Entry Structure: Six Fields and Their Offsets

UEFI Specification 2.10, Section 5.3.3 defines the standard 128-byte GPT partition entry structure:

Campo	Relative offset	Comprimento	Significado
`PartitionTypeGUID`	`0x00–0x0F`	16 bytes	Intended partition type
`UniquePartitionGUID`	`0x10–0x1F`	16 bytes	Identifier for this specific partition
`StartingLBA`	`0x20–0x27`	8 bytes	First logical block
`EndingLBA`	`0x28–0x2F`	8 bytes	Last logical block, inclusive
`Atributos`	`0x30–0x37`	8 bytes	64-bit attribute mask
`PartitionName`	`0x38–0x7F`	72 bytes	Name stored as UTF-16LE code units

These offsets start at the beginning of one entry, not at the beginning of the disk. Also, 128 bytes is the common entry size, not the only legal one. Under UEFI 2.10, SizeOfPartitionEntry must equal 128 × 2^n, with nonnegative integer n. For larger entries, bytes beyond offset 0x7F are reserved and must be zero.

The two GUID fields

PartitionTypeGUID tells software what kind of partition an entry describes. UniquePartitionGUID identifies the particular partition. For example, two Basic Data partitions may share a type GUID but should not share a unique partition GUID.

Neither field is the GPT disk identifier. The DiskGUID belongs to the GPT Header.

LBA boundaries and partition size

A GPT partition entry stores both endpoints as unsigned, little-endian 64-bit integers. Because EndingLBA is inclusive, calculate the block count and capacity as follows:

Block count = EndingLBA − StartingLBA + 1

Size in bytes = Block count × Logical block size

If a partition runs from LBA 2048 through LBA 4095, it spans 2,048 blocks. With 512-byte logical blocks, its size is 1 MiB. With 4096-byte logical blocks, its size is 8 MiB. Never assume that an LBA always represents 512 bytes.

Attributes and partition name

O Atributos field holds a 64-bit mask. UEFI defines bit 0 as Required Partition, bit 1 as No Block I/O Protocol, and bit 2 as Legacy BIOS Bootable. Under UEFI 2.10, bits 3–47 are reserved, while bits 48–63 are partition-type-specific.

For applicable Windows partition types, Microsoft’s GPT partition information documentation defines high-bit flags, including read-only (bit 60), shadow copy (61), hidden (62), and no default drive letter (63). Do not apply those Windows meanings indiscriminately to every partition type.

PartitionName contains 36 UTF-16 code units (72 bytes). A shorter name uses null termination. Importantly, this GPT name is distinct from the volume label stored within a file system. Reading a GPT partition entry alone does not establish the label that Windows displays for a mounted volume.

How the GPT Partition Entry Array Works

O GPT partition entry array holds consecutive slots of equal size. Its GPT Header specifies PartitionEntryLBA, NumberOfPartitionEntries, e SizeOfPartitionEntry. Therefore, software reads the Header before it can reliably locate a particular record.

Array bytes = NumberOfPartitionEntries × SizeOfPartitionEntry

Array logical blocks = ceiling(Array bytes ÷ Logical block size)

UEFI 2.10 requires at least 16,384 bytes of space for the Entry Array. A common configuration uses 128 slots of 128 bytes each. Consequently, it occupies 32 blocks on a 512-byte logical-block disk, or four blocks on a 4096-byte disk. However, 128 is not a universal partition limit. The Header specifies the entry count.

An unused slot has a zero PartitionTypeGUID; its other bytes should also be zero in a properly maintained array. So 128 available slots do não mean 128 active partitions.

Find a specific entry by index

To find entry i, where i begins at zero, use:

Absolute byte offset = (PartitionEntryLBA × Logical block size) + (i × SizeOfPartitionEntry)

Por exemplo, suponha que PartitionEntryLBA = 2, SizeOfPartitionEntry = 128, e i = 5.

Logical block size	Calculated absolute offset	Position on disk
512 bytes	`(2 × 512) + (5 × 128) = 1664`	LBA 3, byte 128
4096 bytes	`(2 × 4096) + (5 × 128) = 8832`	LBA 2, byte 640

These are calculations for a declared example, not observations of two physical devices. Notice that the same GPT partition entry index can fall in different LBAs when the device’s logical block size changes.

Primary and backup arrays

A conventional GPT disk places its primary Header at LBA 1 and its backup Header at the final LBA. The primary Entry Array normally follows the primary Header; the backup array sits before the backup Header. Their locations come from the respective Header fields, not a universal hard-coded sector range.

Nosso GPT Header structure and CRC32 guide explains these Header fields and the relationship between the two arrays in detail.

GPT Partition Type GUID vs. Unique Partition GUID

A GPT partition type GUID describes the intended use of the partition. A Unique Partition GUID identifies a particular partition, while the Disk GUID identifies the GPT disk. These three identifiers are related but are not interchangeable.

Common Windows-related type GUIDs include:

Partition type	Type GUID
Partição do sistema EFI	`C12A7328-F81F-11D2-BA4B-00A0C93EC93B`
Microsoft Reserved	`E3C9E316-0B5C-4DB8-817D-F92DF00215AE`
Microsoft Basic Data	`EBD0A0A2-B9E5-4433-87C0-68B6B72699C7`
Microsoft Recovery	`DE94BBA4-06D1-4D40-A16A-BFD50179D6AC`

A type GUID does não directly identify a file system. For example, a Microsoft Basic Data partition could hold NTFS, FAT32, or exFAT. To recognize its file system, software must inspect data inside the partition.

Likewise, not every GPT disk has an EFI System Partition. An ordinary GPT data disk may not need one.

When copying disks, duplicate unique identifiers can also matter. UEFI requires GPT-aware copying software to generate appropriate new Disk GUIDs and Unique Partition GUIDs. A raw clone may preserve identifiers instead, so never assume that an exact copy has newly generated GUIDs.

Decode a GPT Partition Entry from Hex

Here is the article’s worked technical example: a synthetic GPT partition entry built from the UEFI field layout. It is internally consistent as a single entry, but it is not a complete GPT disk image or a real-world experiment.

Campo	Decoded example
Tipo	Microsoft Basic Data
Type GUID	`EBD0A0A2-B9E5-4433-87C0-68B6B72699C7`
Unique GUID	`01234567-89AB-4CDE-8123-001122334455`
Starting LBA	2048
Ending LBA	4095
Atributos	`0x0000000000000000`
Partition Name	`DATA`

ON-DISK STRUCTURE · EDUCATIONAL SAMPLE

GPT Partition Entry · 128 bytes

Read-only illustration

Select a field or click any byte to see its on-disk value and decoded meaning.

OFFSETHEX BYTES (00–0F PER ROW)ASCII

SELECTED FIELD

Raw bytes (on disk)

Decoded value

LBA size comparisonThe same 2048–4095 LBA range spans different byte capacities.

Logical block size 512 B 4096 B

Partition size1 MiB

Start byte offset1,048,576

Synthetic Basic Data partition entry, not a WinHex capture or a reading from your device. The entry is internally consistent; no complete disk layout or GPT header CRC is asserted.

Step 1: Decode the type GUID

The first 16 bytes are:

A2 A0 D0 EB E5 B9 33 44 87 C0 68 B6 B7 26 99 C7

The on-disk GUID representation uses little-endian byte order for its first 4-byte, 2-byte, and 2-byte components. Therefore:

A2 A0 D0 EB torna-se EBD0A0A2.
E5 B9 torna-se B9E5.
33 44 torna-se 4433.
The remaining eight bytes produce 87C0-68B6B72699C7.

The complete value is the Microsoft Basic Data type GUID. See Microsoft’s GUID representation specification for the underlying encoding.

Step 2: Decode the LBA fields

At relative offset 0x20, the bytes 00 08 00 00 00 00 00 00 represent decimal 2048 in little-endian order.

Em 0x28, FF 0F 00 00 00 00 00 00 represents decimal 4095. Therefore, this GPT partition entry describes 2,048 logical blocks, not 2,047.

If the device exposes 512-byte logical blocks, the starting byte offset equals 2048 × 512 = 1,048,576. If it exposes 4096-byte blocks, the corresponding offset is 8,388,608.

Step 3: Decode attributes and name

The example’s attribute bytes are all zero, so no attribute bits are set. At relative offset 0x38, the name starts with 44 00 41 00 54 00 41 00, which decodes to DATA in UTF-16LE.

A hex editor’s ASCII column may show D.A.T.A. because it treats the zero bytes as nonprintable characters. However, those periods are not part of the partition name.

Together, these steps let you move from raw bytes to a readable GPT partition entry without treating GUID text, LBA values, and UTF-16LE text as if they shared one encoding.

How to Validate a GPT Partition Entry

A decoded GPT partition entry is not necessarily a valid description of the disk. Check its fields against the GPT Header and other active entries.

Verificar	O que verificar	Por que é importante
Active slot	`PartitionTypeGUID` is not all zero	All-zero type marks an unused slot
LBA order	`StartingLBA ≤ EndingLBA`	Rejects reversed or empty ranges
Usable range	Both endpoints fall between `FirstUsableLBA` e `LastUsableLBA`	Keeps partitions out of reserved GPT space
Overlap	Active entries describe disjoint ranges	Avoids conflicting partition descriptions
Identifiers	Appropriate nonduplicate Unique Partition GUIDs	Avoids identity conflicts
Reserved bits	Required reserved bits and bytes are zero	Checks compliance with the entry format

These checks reveal metadata consistency, not the original cause of a failure. A GPT partition entry is only one part of a broader disk-layout check. A boundary can be invalid even when its two 64-bit fields decode without error.

CRC32 checks cover the whole Entry Array

GPT does not store a CRC32 in each entry. Instead, the Header stores PartitionEntryArrayCRC32, calculated over exactly NumberOfPartitionEntries × SizeOfPartitionEntry bytes. This range includes unused entry slots, but excludes any logical-block padding after the declared array length.

If software modifies a GPT partition entry, it must update the Array CRC32 and then the corresponding Header CRC32. A matching checksum means that the bytes agree with the recorded checksum. It does não prove the partition boundaries, identifiers, or file system are correct.

For a complete integrity review, also compare the primary and backup GPT metadata. However, do not assume that a backup always preserves an older partition layout.

GPT validity is not file-system validity

A GPT partition entry may accurately point to a partition whose NTFS or exFAT structures are damaged. Conversely, a deleted entry may leave much of the underlying data untouched. The partition table and the file system occupy different structural layers, so they require different checks.

Missing or Corrupted GPT Partition Entry: What Changes?

An unused slot, a deleted partition definition, and a damaged record are not identical:

Unused: Its type GUID is zero, and a properly cleared slot has zero values in the remaining fields.
Excluído: A partitioning operation removes the definition from the active GPT layout. Depending on what else the operation does, the old file-system data may remain.
Corrompido: A record contains inaccurate or conflicting information, such as an incorrect LBA boundary or GUID.

Windows may show the affected region as Unallocated or fail to mount a volume. Still, those symptoms alone cannot identify which GPT partition entry field changed.

A valid backup array can sometimes help determine the intended layout. Yet a normal deletion may update both arrays, and an outdated backup may contain obsolete addresses. Therefore, restoring a record solely because it appears in a backup is unsafe.

If important data is at risk, avoid formatting, initializing, running destructive partition commands, or rewriting GPT metadata before preserving the source. If the drive repeatedly disconnects or reports serious read errors, stop unnecessary access.

GPT Partition Entry vs. MBR Partition Entry

O GPT partition entry provides more metadata than an MBR partition record, which occupies only 16 bytes.

Recurso	GPT	MBR
Typical entry size	128 bytes	16 bytes
Partition type	128-bit GUID	8-bit type code
Partition identifier	Unique Partition GUID	No equivalent per-entry GUID
Range	64-bit starting and ending LBAs	32-bit starting LBA and sector count
Nome	UTF-16LE field	No partition-name field
Built-in metadata redundancy	Primary and backup structures	No built-in backup partition table

MBR supports extended partitions to provide additional logical volumes. GPT instead uses an array whose slot count is declared in the Header. See the MBR partition table for its record format.

GPT vs. MBR — Interactive Partition Table Explorer

Interactive storage guide

GPT vs. MBR: See the Structural Difference

Compare the disk layouts and inspect the structure of each partition record.

GPT vs. MBR

GPT disk layout

Modern structure

Primary and backup metadata; partition records live in arrays.

Disk regions · select a region

Common GPT layout. Exact array locations and sizes are defined by the headers.

Choose a GPT regionClick any block above to inspect its role.

MBR disk layout

Legacy structure

The first sector contains boot code and four partition-table entries.

Disk regions · select a region

Conceptual MBR layout. Extended partitions are optional.

Choose an MBR regionClick any block above to inspect its role.

Record structure comparison

Partition record fields: 128 bytes vs. 16 bytes

Record size at a common scale

GPT · 128 B

Tipo

Único

Partition Name

MBR · 16 B

GPT: 16 + 16 + 8 + 8 + 8 + 72 = 128 bytes MBR: 1 + 3 + 1 + 3 + 4 + 4 = 16 bytes

At this shared scale, one GPT entry is eight times the size of one MBR entry. The colored field blocks in the two cards below are interactive.

Select a colored field below to inspect its size and purpose.

GPT partition entry · 128 bytes (common)

Six defined fields describe type, identity, boundaries, attributes, and name.

Select a GPT fieldIts length, encoding, and purpose will appear here.

MBR partition entry · 16 bytes

Four slots are stored in the MBR sector. Each slot uses a compact legacy record.

Select an MBR fieldIts length, encoding, and purpose will appear here.

What changes when you use GPT instead of MBR?

Recurso	GPT	MBR
Record size	128 bytes is common; Header defines entry size and count.	16 bytes per entry; four top-level slots in the MBR.
Partition type	128-bit GUID	8-bit type code
Abordando	64-bit starting and ending LBA	32-bit starting LBA and sector count
Partition count	Depends on the Entry Array size	Four primary-table slots; one may be an extended partition
Metadata redundancy	Primary and backup GPT metadata	No built-in backup partition table

The key distinction

GPT is not simply a larger partition record. It uses a Header-defined array, GUID-based identifiers, 64-bit LBA boundaries, and backup metadata. MBR uses a compact 16-byte record and a four-slot table in the first sector.

Teaching example based on the GPT format defined by UEFI and the legacy MBR partition-record layout. The diagrams summarize structure; they do not read or modify a disk.

Conclusão

A GPT partition entry connects a partition’s identity to its logical-block range. Its six fields explain what the partition is meant to be, where it resides, and which attributes apply. By combining the GPT partition entry structure, Header-defined array offsets, GUID decoding, and boundary checks, you can interpret GPT metadata without confusing it with the file system or assuming that a valid CRC32 proves the data is healthy.

PERGUNTAS FREQUENTES

Is every GPT partition entry exactly 128 bytes?

No. UEFI 2.10 permits entry sizes of 128 × 2^n bytes. The Header's SizeOfPartitionEntry field tells a parser the actual size. Thus, a parser that always jumps forward exactly 128 bytes may read larger entries incorrectly.

Can a GPT partition entry array hold more than 128 partitions?

Yes. Many disks reserve 128 slots by default, but the Header controls their number. A larger array can support more slots, subject to applicable specification and implementation constraints. An allocated slot does not automatically mean that an active partition uses it.

Does the GPT partition type GUID tell me whether a partition is NTFS?

No. A Microsoft Basic Data Type GUID does not distinguish NTFS from FAT32 or exFAT. You need evidence from the file-system structures inside the partition. Also, the GUID describes intended purpose, not the health of the contained file system.

Why does the GUID appear reversed in a hex editor?

A GUID's first three binary fields use little-endian ordering. Therefore, a hex editor displays those bytes differently from the standard GUID text. Interpret them by field boundaries rather than reversing all 16 bytes as a single unit.

Is the GPT Partition Name the same as a volume label?

No. The partition name is part of the GPT entry, whereas the volume label belongs to the file system. Their values can differ. Changing a label does not inherently update the GPT name.

Can a GPT partition entry pass CRC32 validation but still be wrong?

Yes. The Entry Array checksum checks stored bytes against a checksum in the Header. It does not check whether LBA ranges overlap, GUIDs identify the intended partitions, or file-system structures remain usable. You must assess these separately.

Does deleting a GPT partition entry erase the files?

Not necessarily. Removing the definition can leave its former data blocks intact, but additional formatting, overwriting, or other device operations may destroy data. Never infer recoverability from a missing entry alone, and avoid writing to a disk that contains important lost data.

Base de Conhecimento

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