The other reason is that on those filesystems file data always occupies a multiple of some unit (a block on Amiga OFS/FFS and a cluster - consisting of multiple blocks - on MS-DOS FAT12) and if the file size doesn't exactly equal that multiple, some bytes of the last block or cluster are wasted where no useful data is stored. The more obvious reason is that you always need to store metadata such as filenames, dates, subdirectories, etc.

Neither of those formats is able to achieve that nominal amount when you sum the sizes of the files stored on disk. The IBM-PC format also stores 512 bytes per sector, but only 9 sectors per track (on a Double Density (DD) disk, as opposed to a High Density (HD) disk), also double sided, also 80 cylinders per disk, which yields 80 * 2 * 9 * 512 = 737280 bytes = 737.28 kB = 720 KiB raw block data.

2 tracks per cylinder) with 80 cylinders per disk, which makes 80 * 2 * 11 * 512 = 901120 bytes = 901.12 kB = 880 KiB raw block data. The Amiga disk format stores 512 bytes per sector, 11 sectors per track (a track is one side of a cylinder), double sided (i.

Ibm formatted floppy disks