"tracks" and "cylinders" are counted from 0, i.e., track 0 is the first (outer-most) track on floppy or other cylindrical disks. old bios code supported ten bits in chs addressing with up to 1024 cylinders (codice_11). adding six bits for sectors and eight bits for heads results in the 24 bits supported by bios interrupt 13h. subtracting the disallowed sector number 0 in codice_12 tracks corresponds to 128 mb for a sector size of 512 bytes (codice_13); and codice_14 confirms the (roughly) 8 gb limit.