GPT
GPT stands for GUID Partition Table. It is made to replace MBR partitioning.
Layout
| LBA 0 | Protective Master Boot Record (PMBR). Holds a partition pointing to GPT to avoid accidental overwrite by old programs. |
| LBA 1 | partition header, can be identified by 8 bytes magic "EFI PART" (45h 46h 49h 20h 50h 41h 52h 54h) |
| LBA 2..33 | partition table entires |
| ...data on disk... | |
| LBA -33..-2 | mirror of partition table |
| LBA -1 | mirror of partition header on last addressable sector |
Partition Table Header
| Offset | Length (bytes) | Description |
| 0x0 | 8 | Signature, can be identified by 8 bytes magic "EFI PART" (45h 46h 49h 20h 50h 41h 52h 54h) |
| 0x8 | 4 | GPT Revision |
| 0xC | 4 | Header size |
| 0x10 | 4 | CRC32 checksum of the GPT header |
| 0x14 | 4 | Reserved |
| 0x18 | 8 | The LBA containing this header |
| 0x20 | 8 | The LBA of the alternate GPT header |
| 0x28 | 8 | The first usable block that can be contained in a GPT entry |
| 0x30 | 8 | The last usable block that can be contained in a GPT entry |
| 0x38 | 16 | GUID of the disk |
| 0x48 | 8 | Starting LBA of the GUID Parition Entry array |
| 0x50 | 4 | Number of Parition Entries |
| 0x54 | 4 | Size (in bytes) of each entry in the Parition Entry array - must be a multiple of 8 |
| 0x58 | 4 | CRC32 of the Partition Entry array. |
| 0x5C | blocksize-0x5C | Reserved (should be zeroed) |
Utilities
The following utilities can handle GPT:
- parted, gparted, gdisk on Linux
- diskutil on MacOSX
- diskpart on Windows (Vista and upwards)
- gpt on MacOSX and BSDs.
Boot loaders
EFI firmware is capable of booting from a specific GPT partition, EFI System Partition which is basically a FAT32 partition. It should contain a slightly modified PE-executable, like ELILO. On old machines with legacy BIOS only you can use GRUB, or you can write a custom boot code.