A sector is a specific format of part of a hard drive, optical drive, floppy disk, flash drive, or other type of storage media. It is also called a disk sector or, less commonly, a block.

Each sector occupies a physical location on the storage device and typically consists of three parts: the sector header, the error correcting code (ECC), and the area where the data is actually stored.

Normally, one sector of a hard disk or floppy disk can hold 512 bytes of information. This standard was established in 1956.

In the 1970s, larger formats such as 1024 and 2048 bytes were introduced to accommodate larger storage capacities. One sector of an optical disk can typically hold 2048 bytes.