Holographic read-only memories accessed by light-emitting diodes

Though it has been recognized for some time that photographic material has the highest information packing density of any present storage medium, preholographic techniques to utilize this capacity required a lens system. Lenses were necessary to use the fine detail storable on film, and precise mechanisms were needed to place this fine detail before a photodetector. Such photographic systems provided an easily made, very large, fixed store in a small size at low cost, but suffered from two major drawbacks: 1. Long access time due to the mechanical nature of the access, and 2. Sensitivity to dust and scratches due to the easily obscured nature of the fine detail carrying the information.