The sector is the area of the data on a magnetic disk, created by low-level formatting during HDD production. It is a minimal information quantity at record or data reading from the magnetic disk by the magnetic head. The sector structure of different models of hard drives differs and is defined by the type of the controller in use and its firmware, but usually, it consists of the data accessible to the user (usually 512 bytes) and the secondary information available only to a hard drive controller:
- The address marker, allowing defining the sector beginning at magnetic disk rotation.
- The unique physical address of the sector in format CHS.
- Reading error correction code (ECC).
- The cyclic redundancy check (CRC) used for checking the data integrity and informing the error correction system of the data corruption.