What is the smallest physical storage unit on a disk called?

The smallest physical storage unit on a disk is called a sector. A sector refers to a subdivision of a track on a magnetic disk or optical disc, and it is the fundamental unit that the disk uses to read and write data. Typically, a sector consists of 512 bytes, although newer hard drives may use 4,096-byte sectors.

Understanding sectors is crucial because they are the way the operating system interfaces with the disk's storage capabilities. When data is accessed, it is done at the sector level, meaning the read/write operations are executed in discrete units defined by the sector size.

In contrast, a block is commonly used in the context of filesystems and can represent a collection of sectors. A track is a concentric circular path on the surface of the disk, which comprises multiple sectors. A cluster, on the other hand, is a group of sectors that the filesystem uses as a logical unit to store files, typically making it larger than a single sector. Thus, the sector is specifically recognized as the smallest unit for physical storage.