5D optical data storage (also branded as Superman memory crystal,[1] a reference to the Kryptonian memory crystals from the Superman franchise) is an experimental nanostructured glass for permanently recording digital data using a femtosecond laser writing process.
[12][13] The "5-dimensional" descriptor is because, unlike marking only on the surface of a 2D piece of paper or magnetic tape, this method of encoding uses two optical dimensions and three spatial co-ordinates to write throughout the material, which suggested the name '5D data crystal'.
[3] The concept is to store data optically in non-photosensitive transparent materials such as fused quartz, which has high chemical stability.
[1][14][15] The storage medium consists of fused quartz, where the spatial dimensions, intensity, polarization, and wavelength are used to modulate data.
It is stored in the Memory of Mankind archive, located in the world's oldest salt mine in Hallstatt, Austria.