Cylinder-head-sector, also known as CHS, was an early method for giving addresses to each physical block of data on a hard disk drive. In the case of floppy drives, for which the same exact diskette medium can be truly low-level formatted to different capacities, this is still true.

Though CHS values no longer have a direct physical relationship to the data stored on disks, virtual CHS values (which can be translated by disk electronics or software) are still being used by many utility programs.

Read more about Cylinder-head-sector:  Definitions, CHS To LBA Mapping, History