FIELD: information technology.
SUBSTANCE: apparatus for recording/displaying data on/from a data storage medium is disclosed. The recordable medium has a plurality of recording layers. A controller in the apparatus controls a reading device and performs optimum power control. The area of the recording layer corresponds to tracks in a bundle, which satisfy the relationship 
where SL, TP, NA and n denote thickness of the intermediate layer between each of the plurality of recording layers and the next recording layer, the track spacing, numerical aperture of the lens and the refraction index of the medium, respectively.
EFFECT: high efficiency of determining optimum recording power.
9 cl, 6 dwg
