Figure 1. Disk structures:
(A) Track
(B) Geometrical sector
(C) Track sector
(D) Cluster

In the context of computer disk storage, a sector is a subdivision of a track (Figure 1, item A) ^[1] on a magnetic disk or optical disc. In computer File systems a cluster is the unit of disk space allocation for files and directories A computer is a Machine that manipulates data according to a list of instructions. Disk storage is a general category of a Computer storage mechanisms in which data is recorded on planar round and rotating surfaces ( disks, discs, or A disk drive track is a circular path on the surface of a disk or diskette on which information is magnetically recorded and from which recorded information is read Magnetic storage and magnetic recording are terms from Engineering referring to the storage of Data on a Magnetized medium Each sector stores a fixed amount of data. The typical formatting of these media provides space for 512 bytes (for magnetic disks) or 2048 bytes (for optical discs) of user-accessible data per sector.

Mathematically, the word sector means a portion of a disk between a center, two radii and a corresponding arc (see Figure 1, item B), shaped like a slice of a pie. A circular sector or circle sector, is the portion of a Circle enclosed by two radii and an arc. In Geometry, a disk (also spelled disc) is the region in a plane bounded by a Circle. Remote Authentication Dial In User Service ( RADIUS) is a networking protocol that provides centralized access authorization and accounting management for people or computers In Geometry, an arc is a closed segment of a Differentiable Curve in the two-dimensional plane; for example a circular Thus, the common disk sector (Figure 1, item C) actually refers to the intersection of a track and mathematical sector.

Early on in various computing fields, the term block was used for this small chunk of data, but sector appears to have become more prevalent. In Computing (specifically data transmission and data storage) block is a sequence of Bytes or Bits having a nominal length (a block size One quite probable reason for this is the fact block has often been applied to data chunks of varying sizes for many types of data streams, rather than being limited to the smallest accessible amount of data on a medium. For example, the Linux program dd allows one to set the block size to be used during execution with the parameter bs=bytes. dd is a common UNIX program whose primary purpose is the Low-level copying and conversion of raw Data. But doing so never changes the actual sector size of a medium, only the size of the blocks that dd will manipulate.

References

1. ^ Such a definition was already being used in 1994 by the ANSI Accredited Standards Committee (ASC) X3 which included, in their ATA-1 X3T10, Revision 4c document, the following definitions: "3. 1. 3 data block. This term describes a data transfer, and is typically a single sector, except when declared otherwise by use of the Set Multiple command. " and "3. 1. 5 LBA (Logical block address). This term defines the addressing mode of the drive as being by the linear mapping of sectors from 1 to n. " And lastly, "9. 9. 4 Word 5: Number of unformatted bytes per sector. " clearly showing their use of sector (rather than block) as the smallest accessible subdivision of a track

See also

• CD-ROM format
• Cylinder-head-sector
• Block (data storage)
• Disk storage
• Disk formatting
• Hard disk drive partitioning
• File Allocation Table