An optical memory disk has a recording layer which is disposed on one surface of a plain circular support base and has a plurality of radially spaced data tracks for storing data items therein, the data tracks being grouped into a number of data track groups. Each of the tracks is divided into a plurality of angularly consecutive sectors bearing a plurality of angularly equally spaced sector marks, respectively, the sector marks on the tracks of each of the data track groups being located in angularly different positions, respectively. There are also disclosed a method of and a system for rapidly and reliably accessing a desired target track among the data tracks on the optical memory disk.