I think foppy size is derived from its physical geometry, so you should write 80*18*2*512 = 1474560 instead meaningless 1.44*1024*1000 even if the result is same. 1.44*1000*1024 is not meaningless. It's historical grown. The predecessor was a 720kB (720*1024) floppy. This floppy size was exactly doubled, making a 1440kB floppy, in short 1.44MB. This should have been 1.406MB, of course, but how could the marketor say he doubled the size of the '720', and then sell you a floppy which is not twice as big?