CHS (cylinder-head-sector)
Disk addressing by three coordinates — cylinder, head and sector — that names a physical location rather than a running number.
An address held the cylinder (the track position toward the spindle), the head (which platter surface) and the sector (the position around the revolution). The model mirrored an old disk's actual geometry, but BIOS INT 13h pinned the fields to 1024 cylinders, 255 heads and 63 sectors. The product of those limits produced the notorious barriers at 504 MB and later 8.4 GB, which a whole generation of drives crashed straight into.
LBA cut the knot by simply numbering the sectors 0…N and letting the drive translate. And since zoned-bit recording arrived, no physical disk has 63 sectors on every track anyway — the geometry a modern drive reports is pure fiction, kept alive for backward compatibility.