Abstract: With no preformatted servo groove structure and simple linear moving instead of conventional disc rotation,a new erasable magneto optical card (MOC) is presented.Its data are written in tracks which are parallel to the width of the card.It possesses the advantages of MO disc erasability and optical card portability.As the defocus tolerance of ±10 μm for focus servo system is set up,the MOC storage system is low-cost and has a good potential markets in medium capacity storage fields.