Reliable digital storage at linear densities as high as 20 000 khzs per mc as result e from a n investigation establishing means of providing optimum recording and reproducing resolution. High linear densities make greater lateral densities practical by reducing interference between tracks. High lateral densities have been demonstrated: 1000 tracks per inch with special head structures, and 4000 tracks per inch with selective-erasure techniques. An area density as high as 32 million bits per square inch has been achieved.These developments remove some of the apparent limits of area density in magnetic recording, and place the emphasis on the necessity for improving reproducing techniques