Stacked Volumetric Optical Disc
The Stacked Volumetric Optical Disc (or SVOD) is an optical disc format developed by Hitachi Maxell which uses an array of wafer-thin optical discs to allow data storage. Each "layer" (a thin polycarbonate disc) holds around 9.4 GB of information, and the wafers are stacked in layers of 20, 25, 100, or more, giving a substantially larger overall data capacity than other optical storage formats; for example, 100× cartridges could hold 940 GB using the system as announced.
Source: Wikipedia — Stacked Volumetric Optical Disc (CC BY-SA 4.0)