with an old bios limit of 1024 cylinders and the ata limit of 16 heads the combined effect was codice_25 sectors, i.e., a 504 mb limit for sector size 512. bios translation schemes known as echs and "revised echs" mitigated this limitation by using 128 or 240 instead of 16 heads, simultaneously reducing the numbers of cylinders and sectors to fit into codice_26 (echs limit: 4032 mb) or codice_27 (revised echs limit: 7560 mb) for the given total number of sectors on a disk.