chs addressing is the process of identifying individual sectors (aka. physical block of data) on a disk by their position in a track, where the track is determined by the head and cylinder numbers. the terms are explained bottom up, for disk addressing the "sector" is the smallest unit. disk controllers can introduce address translations to map logical to physical positions, e.g., zone bit recording stores fewer sectors in shorter (inner) tracks, physical disk formats are not necessarily cylindrical, and sector numbers in a track can be skewed.