Disk Sector

Disk Sector

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 data. Traditional formatting of these storage media provides space for 512 bytes or 2048 bytes of user-accessible data per hertz. Newer hard drives use 4096 byte (4 KB or 4K) Advanced Format sectors.

Mathematically, the word sector means a portion of a disk between a center, two radii and a corresponding arc (see Figure 1, item B), which is shaped like a slice of a pie. Thus, the disk sector (Figure 1, item C) refers to the intersection of a track and mathematical sector.

In disk drives, each physical sector is made up of three basic parts, the sector header, the data area and the error-correcting code (ECC). The sector header contains information used by the drive and controller. This information includes sync bytes, address identification, flaw flag and header parity bytes. The header may also include an alternate address to be used if the data area is undependable. The address identification is used to ensure that the mechanics of the drive have positioned the read/write head over the correct location. The data area contains the recorded user data. The ECC field contains codes based on the data field, which are used to check and possibly correct errors that may have been introduced into the data..