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The basic disk types of Windows were introduced in a previous article, "introduction to disk types for Windows Storage Management." In this article, we will give an in-depth introduction to the structure of two disk types, GPT and MBR.

Windows disk structure:

The mainstream disk structure of Windows is divided into MBR and GPT. MBR was the only option for early Windows, but as the capacity of physical disks increased. GPT structure has become the current mainstream, the maximum support exceeds the capacity of 2TB, provides fault tolerance, multi-partition support, more powerful than MBR.

MBR (Master Boot Record) disk structure:

There are several kinds of information in the MBR in Basic MBR Disk.

Bootstrap Code-also known as Master boot code, is a piece of executable code that scans the partition table of the active partition, finds the start sector of the active partition, loads the boot sector into memory, and so on.

All physical disks of Disk Signature-Windows have a disk signature mechanism, and the data on that disk cannot be accessed without a signed windows. When Windows scans to a new physical disk, try to write some disk signatures to identify the disk. The length of the signature is 8 bytes. It is then written to the first sector at 0x01B8-0x01BB. The signature is stored in the registry in the HKLM\ SYSTEM\ MountedDevices location.

Partition Table-Partition Table, a 64-byte data structure used to define the starting position of each partition. Each partition is defined to be 16 bytes in size. Because of this design, MBR's extended primary partition can only support a maximum of 4.

The disk structure of a simple Basic (MBR) is shown in the following figure. I can see that the outermost is the physical disk (Disk), which contains MBR (Master Boot Record) at the front end of the physical disk. In this example, a partition and NTFS logical volume are defined.

MBR Disk supports up to four primary partitions (Primary Patition), and if you create multiple primary partitions, the structure is as follows. A physical disk contains four primary partitions, each containing a file volume.

If an extended partition is enabled, multiple logical volumes can be included in the extended partition.

GPT (GUID-Globally Unique Identifer) disk structure:

By 2018, most operating systems supported the inclusion of GPT GPT Disk in the main MBR, and the partition table of GPT Disk included the following. In the MBR hard disk, the partition information is stored directly in the master boot record (MBR) (the system's boot program is also stored in the master boot record). However, in the GPT hard disk, the location information of the partition table is stored in the GPT header. However, for compatibility reasons, the first sector of the hard disk is still used as the MBR, followed by the GPT header.

Protective MBR-unlike MBR, which contains primary partition information in Partition Table, GPT Disk is "Protective MBR" in the first sector (Sector) of the disk, which is located in the location of LBA0 (the common storage addressing size is 512 per unit). It contains the partition information of the disk and the initial BIO initiator. This is for compatibility reasons and ensures that some legacy MBR disk tools can recognize GPT Disk.

The Partition Table Header-partition header defines some blocks that can be used on disk, as well as the number and size of Partition Entries that make up the partition table (typically 128bytes). The 64-bit version of Windows Server 2003 and above supported by GPT supports the creation of up to 128partitions with a record size of 128bytes each. The GUID of the disk is also recorded in the partition header, which is used to record its own size and position, as well as the location of the spare GPT header (located in the last sector of the disk). The check value of CRC32 is also included.

Partition entries-GPT Disk describes partitions with simple and straightforward entries. The first 16 bytes are used to identify the partition type. The second 16 is directly used to record the unique GUID of the changed partition. The next three 8-byte records describe the initial LBA address, the ending LBA address, and the partition properties, respectively. The last 72 bytes are partition names. The single partition record size is 128 bytes. Partition entries usually starts with the LBA2 address.

Finally, in order to reduce the risk of corruption of the partition table, GPT saved a copy of the partition table at the end of the hard drive.

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