Data medium for facilitating storing and reading of data, has concentric spiral track comprising cavities of different depths, where each cavity has trapezoidal shape with large base, left part symmetrical to right part and small base

摘要

The medium has a concentric spiral track with cavities of different depths, where data are stored in the cavities. Each cavity has a trapezoidal shape with a large base, a left part symmetrical to the right part and a small base reflecting incident beams. The left parts of the cavities are parallel with a predefined longitudinal interval. The small base is far from the corresponding large base if the respective cavity is deeper.