The size of an HDD can be considered by reproducing the number of cylinders by the quantity of heads by the number of segments by the quantity of bytes/sector. Drives with ATA interface, bigger and in excess of eight gigabytes perform as if they were prearranged into 16383 cylinders, 16 heads, and 63 sectors, for compatibility with older operating systems. Contrasting in the 1980s, the cylinder, which calculates reported to the CPU by up to date ATA drive that has no longer definite physical parameters given that the reported numbers are controlled by historic operating-system boundary and with zone bit recording.