Experimental curves of output as a function of packing density are presented for a thin film medium and two types of head. These curves are then fitted to theoretical predictions in such a way that useful data is determined about the factors which limit the packing density observed. From this secure base, predictions are made about the ultimate attainable packing densities if improvements are made to the limiting parameters. It is shown that packing densities of half a million bits per inch and more along with area densities of 50Gb/in 2 are possible but that substantial improvements to the magnetic and mechanical aspects of disk systems as well as to the signal processing methods are necessary especially if densities of one million bits per inch and 100Gb/in 2 are to be achieved.