It was the first proof of concept test for Project Silica, a Microsoft Research project that uses recent discoveries in ultrafast laser optics and artificial intelligence to store data in quartz glass. A laser encodes data in glass by creating layers of three-dimensional nanoscale gratings and deformations at various depths and angles. Machine learning algorithms read the data back by decoding images and patterns that are created as polarized light shines through the glass.

Not a robust way to store data for a long time because knowledge of either lasers or machine learning to the exact type can be forgotten. Archival needs to be more analog and robust than this. Mind you it's replacing tape, that's low level of technology one would need to reverse engineer, though granted it's far more fragile to the environment.