The optical storage medium comprises tracks with a mark/space data structure, wherein the tracks comprise alternately partitioned marks and not partitioned marks. The partitioned marks are partitioned in particular in tracking direction and are partitioned in two parts, advantageously in two equal parts. The partitions are arranged advantageously such that one track comprises not partitioned marks and a neighboring track comprises partitioned marks, for reducing the track pitch of the optical storage medium and for providing an increased data capacity. The optical storage medium is in a preferred embodiment an optical disc comprising a mask layer with a suitable material for providing a super resolution near field effect, and the data structure of the optical disc comprises two spirals which have either partitioned marks or not partitioned marks. An apparatus for reading the data of a respective optical storage medium comprises a pick-up unit with a laser and a first optical element for providing a TM polarized beam and a TE polarized beam, a second optical element for separating the reflected TM and TE polarized beams, and a first and a second detector.