Where does sector collide?

In geometry a sector is the wedge-shaped region of a disk bounded by two radii and the arc of the circle between them, the familiar pie slice whose area is a fraction of the whole disk set by the central angle. Euclid's Elements treats the sector in its books on circles, relating the angle at the centre to the arc and the region it subtends. The referent is a plane region defined purely by a circle, two radii, and their included angle, and it has no connection to a track on a storage disk or a division of an economy beyond the picture of a slice carved from a whole.[1]

Unit

A region of a disk measured by its central angle and radius

Recovery means

Not applicable

Measured by

Computed from the central angle and radius as a fixed fraction of the disk's area and circumference

In computer storage a sector is the smallest physically addressable unit of a disk: each track of a hard disk or similar device is divided into sectors of fixed byte length, and the drive reads or writes whole sectors at a time. Silberschatz, Galvin, and Gagne's Operating System Concepts describes how the operating system maps logical blocks onto these physical sectors to store and retrieve files. The referent is a hardware storage quantum identified by its position on a track, an entirely different thing from a wedge of a circle or a branch of an economy, sharing only the geometric accident that early disks carved their circular tracks into angular slices.[2]

Unit

A fixed-size addressable block of bytes on a storage track

Recovery means

Not applicable

Measured by

Counted and addressed by logical block number; capacity is sectors per track times bytes per sector