Holography is a way to store a lot of information in interference patterns. This technique has been i n use since the 1940s, originally used with electron microscopy — and later expanded with the invention of lasers. A hologram is the reconstructed image created by interfering wave forms, these waveforms can be reconstructed by producing partial information (a light source) and observing the output at a given reference angle. You shine a light on the hologram, and you see a three dimensional image that changes with your viewing angle. These interference patterns can be from angled scratches in a surface (“Scratch Holograms”), the orientation of crystals in a gel medium (“Photographic Holograms”), or some other interference pattern (“Mist/Fog Holograms”). But a hologram doesn’t need to be an image of something you might recognize, it could be information stored and retrieved base on the angles of illumination and retrieval.
So, instead of the cube (pictured above) appearing on the hologram, we could store a multiple “pixels” that represent various on and off states. By simultaneously storing multiple “images”, we could store 2D video, or other data, and play it back by rotating the image. The entire write operation would happen simultaneously, at least for any given “page” of data, as long as we can split our “illumination beam” and create/block it at various angles (imagine a filter with holes cut in it, one hole for each 1 value, or blocked for a 0 value). This would be possible with current “film” holograms. The trick is that the light source must be coherent (lasers) so that the light waves can interfere on the film surface.