Disk sector - Wikipedia
https://en.wikipedia.org/wiki/Disk_sectorThe first disk drive, the 1957 IBM 350 disk storage, had ten 100 character sectors per track; each character was six bits and included a parity bit. The number of sectors per track was identical on all recording surfaces. There was no recorded identifier field (ID) associated with each sector. The 1961 IBM 1301 disk storageintroduced variable length sectors, termed records by IBM, and added to each record a record address field separate from the data in a record (sector). All moder…