To meet the requirement for a second-generation digital optical disk with a larger capacity and a higher speed, the new 300-mm, write-once optical disk system described here uses pit-edge recording and the modified-constant-angular-velocity method [Maeda et al., Trans. IEICE E74, 951 (1991)]. New techniques that can use these methods together and are suitable for interchangeability—data composition and independent detection of the leading and trailing edges—have resulted in the most reliable data-storage system ever produced, we believe. The concept of this system, the characteristics of the new techniques, and the optimization of system performance are described.