Disk sector

lastmod 2020-07-04created 2020-07-044 edits

In computer disk storage, a sector is a subdivision of a track on a magnetic disk or optical disc. Each sector stores a fixed amount of user-accessible data, traditionally 512 bytes for hard disk drives (HDDs) and 2048 bytes for CD-ROMs and DVD-ROMs. Newer HDDs use 4096-byte sectors, which is called Advanced Format (AF).

The sector is the minimum storage unit of a hard drive. Most disk partitioning schemes are designed so that a file can occupy multiple sectors regardless of its actual size. Files that do not fill an entire sector hold the remainder of the sector filled with zeros. In practice, operating systems usually operate on blocks of data, and these blocks span multiple sectors.

Geometrically, the term sector means a circular sector, and it consists of three basic parts: the sector header, the data area, and the error-correcting code (ECC). The sector header contains information used by the disk and the controller, including sync bytes, address identification information, a flaw flag, and header parity bytes. The header may include an alternative address to be used if the data area cannot be relied upon. The address identification information is used to ensure, through the drive's mechanics, that the read/write head is positioned at the correct location. The data area holds the recorded user data, while the ECC field holds a code based on the data field, which is used to check and correct errors that may have been introduced into the data.

See also

• Hard disk drive (HDD)
• Cylinder-head-sector (CHS)

Favorite site

• What's the point of hard drives reporting their physical sector size?
• [Recommended] WEBDIR :: Understanding the hard disk ¹ (GPT, Disk sector, UEFI, Partition table, CHS, LBA)

References