exFAT (Extended File Allocation Table)

1. Boot Sector:

The boot sector contains metadata about the file system, including:

• Jump Instruction (3 bytes):

  • The initial instruction to jump to the boot code.

• OEM Name (8 bytes):

  • Identifies the system as exFAT.

• Bytes Per Sector (2 bytes):

  • Specifies the size of a sector (commonly 512 bytes).

• Sectors Per Cluster (1 byte):

  • Specifies the number of sectors per cluster.

• Reserved Sectors (4 bytes):

  • Number of sectors reserved for system structures.

• Total Sectors (8 bytes):

  • Total number of sectors in the volume.

• FAT Offset (4 bytes):

  • Offset of the File Allocation Table.

• FAT Length (4 bytes):

  • Length of the FAT in sectors.

• Cluster Heap Offset (4 bytes):

  • Offset of the data region.

• Root Directory Cluster (4 bytes):

  • Starting cluster of the root directory.

• Volume Serial Number (4 bytes):

  • Unique identifier for the volume.

• Boot Code:

  • Bootstrapping code for system startup.

2. File Allocation Table (FAT):

The FAT is a map of clusters on the disk, with each entry:

• Available Cluster: Marked as 0x00000000.

• End-of-Cluster Chain: Marked as 0xFFFFFFFF.

• Used Cluster: Points to the next cluster in the chain for file data.

3. Cluster Heap:

This is the main data region where file and directory data is stored. It begins at the Cluster Heap Offset and is organized into clusters.

4. Root Directory:

The root directory is stored in the Cluster Heap and contains directory entries:

• File Name:

  • Supports Unicode and long file names.

• Attributes:

  • Defines file properties (e.g., read-only, hidden, system).

• Starting Cluster:

  • Indicates where the file's data begins.

• File Size:

  • Specifies the file's size in bytes.